Invest 92L
A tropical wave over the eastern Caribbean Sea was designated "Invest 92L" yesterday evening by the National Hurricane Center. Infrared satellite animations indicate a marked decrease in heavy thunderstorm activity associated with this feature. The likely cause of this is an area of dry air to the east, noted on water vapor animations.
Despite the recent convective downturn, however, CIMSS wind shear analysis indicates an anticyclone has developed aloft over the wave axis, which I estimate based on satellite animations and CIMSS 850 mb vorticity analysis is near 14N 76W.
This system should continue moving generally W throughout the remainder of its lifetime, eventually running into Central America in about two days, with perhaps a slight WNW component developing after 12 hours as the ridge to the north weakens somewhat. This system could take a track very similar to Hurricane Alex earlier in the year. The system should continue WNW even after landfall, and will enter the Bay of Campeche in the Gulf of Mexico in about three days or so, and ultimately make a second landfall from central Mexico to south Texas. The main legacy from this system will be heavy rains across Central America, Mexico, and south Texas.
An alternate scenario is for the system to move a bit more southward (though I'd still expect a slight N component of motion even with this arrangement) and eventually move into the Eastern Pacific.
Though upper-level winds favor development over the next seven days, I am not expecting any development from this feature. None of the computer models even remotely hint at its development, either.
Remnants of Colin
The remnants of former Tropical Storm Colin are located in the western Atlantic Ocean, several hundred miles northeast of Puerto Rico. Infrared satellite animations indicate that deep convection has remained fairly persistent across the system over the last couple of hours. Indeed, this system has been producing persistent deep convection over at least the last 18 hours. This can probably be attributed to a significant slowing of the forward speed over the last 24 hours, as Colin has gradually moved underneath the influence of a strong weakness in the western Atlantic subtropical ridge.
The center of Colin is still not particularly well-defined based on various satellite animations, along with various microwave satellite images from the Navy Research Lab (NRL). Unfortunately, a recent ASCAT pass failed to capture all of Colin, but it too suggests that the circulation is poorly defined, with no evidence of westerly winds along the southern side of the circulation center.
This system has some dry air to contend with to the west, being induced by an upper-level cold cored low pressure system centered near 26N 73W. Additionally, CIMSS analysis depicts 20 kt of westerly vertical shear blowing across the system.
The track for this system has finally become more clear, with the models now unanimously calling for recurvature out to sea underneath the influence of a strong cold front currently moving across the central United States. This system will further erode the western periphery of the Atlantic subtropical ridge, and allow the system to turn N by 36-48 hours, with a gradual deceleration in the forward speed from now until 48 hours.
Colin is moving NW at the moment, but as previously noted, a turn to the N is expected over the next day or two as the ridge weakens further with the approach of the aforementioned front. Thereafter, a gradual increase in forward speed, particularly after 72 hours, is expected as the system becomes well-embedded within the westerlies. The only land areas potentially threatened by this system are Bermuda and the Canadian Maritimes. The models suggest that the former will be impacted by the system in three days, and Colin be a hurricane as it approaches that island. Residents there should be carefully monitoring the progress of this system over the next several days.
Upper-level winds should begin to ease somewhat by tomorrow, and particularly after 36 hours. It is still possible that Colin will become a hurricane, and I actually find it quite likely. Its best chance would be after 72 hours, when the shear will be at its lowest.
Elsewhere
Elsewhere, a tropical wave along 30W is the next threat to develop. Most of the models are developing this feature. Right now its track is uncertain, but it could follow a path out to sea like Colin. This is highly speculative, though. Upper-level winds favor gradual development over the next several days.
Wednesday, August 4, 2010
Monday, August 2, 2010
Tropical weather analysis - August 2, 2010
Tropical Depression Four
Tropical Depression Four was able to develop this morning from former Invest 91L. As of 5:00 PM EDT, the National Hurricane Center had it centered at 13.0°N 42.5°W, moving WNW at 16 mph, with a pressure of 1006 mb. It should be noted that this system appears to be moving more westerly as of the last couple of hours, and it will be interesting to see how the NHC will respond to this in the upcoming advisory. The newly-developed tropical cyclone is moving rather quickly, and I think that it might have even increased in forward speed from the earlier estimated 16 mph. Indeed, since the time of the previous advisory, it has jumped from 42W to 44W. The last of the visible satellite animations suggest that the cyclone may be experiencing some slight southeasterly to easterly shear, with most of the deep convection confined to the western portion of the circulation.
This shear is being induced by a developing upper-level anticyclone to the east of the depression. Another possible explanation for this (since the shear associated with the anticyclone isn't prohibitively strong, only 10 kt) is that the brisk forward speed of the tropical cyclone is making it difficult for sustenance of low-level convergence. Indeed, there have been many tropical cyclones that have dissipated for this reason, despite favorable atmospheric conditions. This remains a possible scenario with Tropical Depression Four. Indeed, a recent SSMIS microwave overpass indicates that the surface circulation is elongated and not well-defined. However, the circulation is probably still closed off, based on animation of RGB satellite loops. However, if the forward speed increases anymore, the cyclone may not be able to maintain a closed surface circulation, and also may not significantly intensify, due to lack of low-level convergence.
There is also a noticeable vertical tilt associated with the cyclone, based on CIMSS vorticity data. This further suggests that the cyclone is having trouble, and the low-level center may be outrunning the mid-level center. Despite the cyclone's recent W movement, steering data suggests that a turn to the WNW should soon begin once again, with perhaps an additional increase in the forward speed over the next 12 hours. This general motion should continue until around 72 hours, when the cyclone encounters a large break in the Atlantic subtropical ridge forecast by most of the model guidance. At that point, a gradual deceleration is expected as the aforementioned ridge weakens with the approach of a mid- to upper-level trough currently stretching from eastern New Mexico to central Kansas. This will be the key player in whether or not the tropical cyclone harmlessly recurves out to sea, or makes a strike somewhere along the eastern United States mainland.
The models all agree on bringing the trough across the western Atlantic in about three days, but differ greatly on its overall strength and amplitude. The CMC, GFS, and NOGAPS models foresee a less amplified trough, which keeps enough ridging in place to prevent a complete recurvature. The GFDL, HWRF, and ECMWF models foresee a more amplified upper trough, with less ridging and more troughing, which would tend to favor a sharp poleward turn during the day four to five timeframe, which would lead to eventual recurvature.
My current thinking is that the pattern should remain less amplified and more zonal than the latter three models are predicting. This is based primarily upon climatology, which strongly argues against such a large break occurring in the Atlantic subtropical ridge. However, one must keep in mind the unseasonably strong longwave troughs that recurved both 2004's Charley and 2009's Bill. There is greater than normal uncertainty in the track forecast for this system, and I would put the odds of an east coast strike and an eventual recurvature at 50/50. But again, I tend to favor the former scenario, due to the time of the year. Nevertheless, if consistency is shown with regards to a more amplified upper air pattern, I will have to shift my forecast track significantly to the right as the days press on.
Due to the uncertainty in the forecast track, residents all along the east coast from Florida to Maine should carefully monitor the progress of the depression over the next several days. Bermuda should as well, since even if the cyclone completely misses the United States east coast, it could still cause problems for them. Indeed, the GFDL, HWRF, and ECMWF all foresee the cyclone coming very near that island late on day four and into day five.
In the meantime, the cyclone should move north of the Leeward Islands and Puerto Rico in about two and a half days. Residents in those areas should also closely monitor the progress of this system, as tropical storm watches or warnings could be required over the next day or so, depending on how far west the cyclone moves in relation to the current NHC forecast track. All in all, my own forecast track is in strong agreement with the NHC's 5:00 PM one.
The intensity forecast is problematic. If the cyclone fails to maintain a closed surface circulation, it will probably never regenerate, due to strong upper-level shear forecast by the GFS to persist north of the Greater Antilles and Leeward Islands for the next several days. On the other hand, if it remains a tropical cyclone and the anticyclone follows it, it could withstand the shear even as it approaches that shear by 60 hours or so. None of the models, save the GFDL and CMC, are significantly intensifying the tropical cyclone. However, I will err on the side of caution and forecast gradual intensification over the next three days or so.
Thereafter, the cyclone is forecast to lose its upper-level anticyclone, and vertical shear is still expected to be prohibitive across the western Atlantic, albeit not quite as strong as what's currently forecast north of the Leeward Islands. I will call for a leveling off of the intensity at that point, though a gradual weakening could certainly commence.
There is only a small chance, about 15%, of TD4 becoming a hurricane.
Elsewhere
Elsewhere in the tropics, a tropical wave is moving across the extreme eastern Caribbean Sea. Upper-level winds support development of this disturbance as it moves WNW at 15 to 20 mph over the next couple of days. By day three, the system will be approaching a weakness at the western end of the Atlantic subtropical ridge, and will probably enter the Gulf of Mexico in about five days. The biggest inhibiting factor is proximity to South America, which has been known to destroy rather healthy tropical waves, and even tropical cyclones, in this area.
The models nevertheless eventually develop the system, with the 18z GFS calling for a rather powerful hurricane impacting southeastern Louisiana in a week, while the 12z CMC suggests that the system will eventually run into Central America. This scenario appears unrealistic for now, given the synoptic scale pattern across North America and the western Atlantic Ocean. The 12z NOGAPS hints at development as the system approaches the western Caribbean in six days. I feel the NOGAPS solution, while plausible in terms of development, is much too slow with the forward speed of the system. The 18z GFDL hints at development of this feature as well. Finally, the 12z ECMWF does not develop this system.
Tropical Depression Four was able to develop this morning from former Invest 91L. As of 5:00 PM EDT, the National Hurricane Center had it centered at 13.0°N 42.5°W, moving WNW at 16 mph, with a pressure of 1006 mb. It should be noted that this system appears to be moving more westerly as of the last couple of hours, and it will be interesting to see how the NHC will respond to this in the upcoming advisory. The newly-developed tropical cyclone is moving rather quickly, and I think that it might have even increased in forward speed from the earlier estimated 16 mph. Indeed, since the time of the previous advisory, it has jumped from 42W to 44W. The last of the visible satellite animations suggest that the cyclone may be experiencing some slight southeasterly to easterly shear, with most of the deep convection confined to the western portion of the circulation.
This shear is being induced by a developing upper-level anticyclone to the east of the depression. Another possible explanation for this (since the shear associated with the anticyclone isn't prohibitively strong, only 10 kt) is that the brisk forward speed of the tropical cyclone is making it difficult for sustenance of low-level convergence. Indeed, there have been many tropical cyclones that have dissipated for this reason, despite favorable atmospheric conditions. This remains a possible scenario with Tropical Depression Four. Indeed, a recent SSMIS microwave overpass indicates that the surface circulation is elongated and not well-defined. However, the circulation is probably still closed off, based on animation of RGB satellite loops. However, if the forward speed increases anymore, the cyclone may not be able to maintain a closed surface circulation, and also may not significantly intensify, due to lack of low-level convergence.
There is also a noticeable vertical tilt associated with the cyclone, based on CIMSS vorticity data. This further suggests that the cyclone is having trouble, and the low-level center may be outrunning the mid-level center. Despite the cyclone's recent W movement, steering data suggests that a turn to the WNW should soon begin once again, with perhaps an additional increase in the forward speed over the next 12 hours. This general motion should continue until around 72 hours, when the cyclone encounters a large break in the Atlantic subtropical ridge forecast by most of the model guidance. At that point, a gradual deceleration is expected as the aforementioned ridge weakens with the approach of a mid- to upper-level trough currently stretching from eastern New Mexico to central Kansas. This will be the key player in whether or not the tropical cyclone harmlessly recurves out to sea, or makes a strike somewhere along the eastern United States mainland.
The models all agree on bringing the trough across the western Atlantic in about three days, but differ greatly on its overall strength and amplitude. The CMC, GFS, and NOGAPS models foresee a less amplified trough, which keeps enough ridging in place to prevent a complete recurvature. The GFDL, HWRF, and ECMWF models foresee a more amplified upper trough, with less ridging and more troughing, which would tend to favor a sharp poleward turn during the day four to five timeframe, which would lead to eventual recurvature.
My current thinking is that the pattern should remain less amplified and more zonal than the latter three models are predicting. This is based primarily upon climatology, which strongly argues against such a large break occurring in the Atlantic subtropical ridge. However, one must keep in mind the unseasonably strong longwave troughs that recurved both 2004's Charley and 2009's Bill. There is greater than normal uncertainty in the track forecast for this system, and I would put the odds of an east coast strike and an eventual recurvature at 50/50. But again, I tend to favor the former scenario, due to the time of the year. Nevertheless, if consistency is shown with regards to a more amplified upper air pattern, I will have to shift my forecast track significantly to the right as the days press on.
Due to the uncertainty in the forecast track, residents all along the east coast from Florida to Maine should carefully monitor the progress of the depression over the next several days. Bermuda should as well, since even if the cyclone completely misses the United States east coast, it could still cause problems for them. Indeed, the GFDL, HWRF, and ECMWF all foresee the cyclone coming very near that island late on day four and into day five.
In the meantime, the cyclone should move north of the Leeward Islands and Puerto Rico in about two and a half days. Residents in those areas should also closely monitor the progress of this system, as tropical storm watches or warnings could be required over the next day or so, depending on how far west the cyclone moves in relation to the current NHC forecast track. All in all, my own forecast track is in strong agreement with the NHC's 5:00 PM one.
The intensity forecast is problematic. If the cyclone fails to maintain a closed surface circulation, it will probably never regenerate, due to strong upper-level shear forecast by the GFS to persist north of the Greater Antilles and Leeward Islands for the next several days. On the other hand, if it remains a tropical cyclone and the anticyclone follows it, it could withstand the shear even as it approaches that shear by 60 hours or so. None of the models, save the GFDL and CMC, are significantly intensifying the tropical cyclone. However, I will err on the side of caution and forecast gradual intensification over the next three days or so.
Thereafter, the cyclone is forecast to lose its upper-level anticyclone, and vertical shear is still expected to be prohibitive across the western Atlantic, albeit not quite as strong as what's currently forecast north of the Leeward Islands. I will call for a leveling off of the intensity at that point, though a gradual weakening could certainly commence.
There is only a small chance, about 15%, of TD4 becoming a hurricane.
Elsewhere
Elsewhere in the tropics, a tropical wave is moving across the extreme eastern Caribbean Sea. Upper-level winds support development of this disturbance as it moves WNW at 15 to 20 mph over the next couple of days. By day three, the system will be approaching a weakness at the western end of the Atlantic subtropical ridge, and will probably enter the Gulf of Mexico in about five days. The biggest inhibiting factor is proximity to South America, which has been known to destroy rather healthy tropical waves, and even tropical cyclones, in this area.
The models nevertheless eventually develop the system, with the 18z GFS calling for a rather powerful hurricane impacting southeastern Louisiana in a week, while the 12z CMC suggests that the system will eventually run into Central America. This scenario appears unrealistic for now, given the synoptic scale pattern across North America and the western Atlantic Ocean. The 12z NOGAPS hints at development as the system approaches the western Caribbean in six days. I feel the NOGAPS solution, while plausible in terms of development, is much too slow with the forward speed of the system. The 18z GFDL hints at development of this feature as well. Finally, the 12z ECMWF does not develop this system.
Sunday, August 1, 2010
Tropical weather analysis - August 1, 2010
Invest 91L
A well-defined tropical wave located several hundred miles west-southwest of the Cape Verde Islands (dubbed "Invest 91L" by the National Hurricane Center) continues to gradually become better organized, and a tropical depression could be forming, according to a statement from the NHC's 2PM EDT Tropical Weather Outlook:
A LARGE LOW PRESSURE SYSTEM CENTERED ABOUT 875 MILES WEST-SOUTHWEST
OF THE CAPE VERDE ISLANDS IS MOVING WESTWARD TO WEST-NORTHWESTWARD
AT 5 TO 10 MPH. SHOWER AND THUNDERSTORM ACTIVITY IS GRADUALLY
BECOMING BETTER ORGANIZED AND A TROPICAL DEPRESSION MAY BE FORMING.
IF THIS CURRENT DEVELOPMENT TREND CONTINUES...THEN ADVISORIES ON
THIS DISTURBANCE COULD BE INITIATED AS EARLY AS THIS AFTERNOON OR
EVENING. THERE IS A HIGH CHANCE...80 PERCENT...OF TROPICAL CYCLONE
FORMATION DURING THE NEXT 48 HOURS.
Based on the last of the visible satellite animations, it appears that the center is located at 10N 36W. Deep convection appears to be firing near or over the estimated center, and the aforementioned satellite animations depict that a closed surface circulation is rapidly trying to form, though this is not a particularly well-defined one as of yet. Also, upper-level outflow appears to be developing to the north and west of the system, but it is not well-defined as of yet. There is currently no outflow along the south and eastern sides of the circulation, which is to be expected due to competing influence from the ITCZ to the south, as well as moderate easterly to vertical wind shear that the system has been experiencing for the last couple of days.
However, this shear may be relaxing now over the estimated center position, based on low cloud motions indicated in various satellite animations as well as CIMSS wind shear analysis, which depicts only 5 kt of shear over the system, amidst a developing anticyclone aloft. As far as the track forecast is concerned, both CIMSS steering data and animation of water vapor imagery depict a gradual weakness developing in the Atlantic subtropical ridge to the north of the system. This weakness is being caused by a mid- to upper-level trough over the western Atlantic, and a developing upper-level low near 23N 61W that has recently pinched off from the trough. This weakness occurred a little sooner than I had expected this time yesterday, but nevertheless it is quite evident at this point.
It is because of this slight weakness that 91L has turned WNW this evening. Analysis of mid- to upper-level steering layers, along with data from the 18z GFS, indicates that this trough is not particularly well-defined, and more importantly, that the majority of the energy associated with this trough should remain far to the north of Invest 91L. This, along with the fact that the aforementioned upper low is forecast to gradually de-amplify and weaken, will not allow the subtropical ridge to weaken significantly over the next couple of days. Hence, 91L should continue moving toward the WNW over the next couple of days, with an increase in forward speed expected to begin over the next day or so.
This will allow 91L to gain some additional latitude and take greater advantage of the Coriolis force, producing greater cyclonic vorticity. By three days, the models unanimously forecast a rather large break to occur in the Atlantic subtropical ridge as another trough, located over the western United States, emerges into the western Atlantic.
My current thinking though, based on the current large-scale pattern across the United States, is that the overall strength of this trough is being vastly overestimated by the models. Even if it does end up being that powerful, I think it will lift out far faster than what most of the models are indicating this evening. I agree most strongly with the 12z ECMWF, and I expect more ridging than is currently being indicated by most of the models. This puts the greatest United States risk area at the east coast of Florida. However, this is a long-range forecast track, and as such, is highly uncertain. Nevertheless, residents along the east coast from Florida to North Carolina should carefully monitor the progress of this system over the next week or so.
First and foremost though, residents across the northern Leeward Islands, the Virgin Islands, and Puerto Rico, should closely monitor the progress of this system over the next several days, as the system could pass just north of that area in about four days.
Interestingly, the models are rather slow in developing this system, with only the CMC and ECMWF developing the system within the next two days. I have opted to go with these models, based on current organizational trends observed with Invest 91L. Upper-level winds favor additional development of this system, and the 18z GFS strengthens the aforementioned anticyclone, keeping it intact even as the system runs into strong westerly vertical shear associated with the TUTT north of the Leeward Islands in four days. This anticyclone may not allow much in the way of weakening when the system encounters shear from the TUTT.
Thereafter, as the system nears the western Atlantic, the upper air pattern is forecast to continue being zonal and unfavorable, with a positive twist: the GFS suggests that the anticyclone should begin to fade after four days. This would tend to weaken the system by day five as it approaches the western Atlantic. However, this shear is forecast to lift out relatively quickly, and it is not likely to completely destroy the system.
All in all, this system has developed much quicker than I thought it would. As such, I expect this system to become a tropical depression tonight or tomorrow morning. Again, residents across the northern Leeward Islands, the Virgin Islands and Puerto Rico, should closely monitor the progress of this system over the next several days.
Southwest Caribbean tropical wave
A tropical wave located a couple hundred miles east of the coast of Nicaragua continues to produce disorganized showers and thunderstorms. This system has become a little better organized this evening, owing to the long foreseen relaxation of the upper-level winds. However, proximity to land is expected to inhibit any significant development, and the system should move inland across Nicaragua sometime tomorrow morning. Regardless of development, locally heavy rainfall and strong gusty winds will overspread portions of Nicaragua, Honduras, Panama, El Salvador, and Costa Rica tonight and tomorrow.
A well-defined tropical wave located several hundred miles west-southwest of the Cape Verde Islands (dubbed "Invest 91L" by the National Hurricane Center) continues to gradually become better organized, and a tropical depression could be forming, according to a statement from the NHC's 2PM EDT Tropical Weather Outlook:
A LARGE LOW PRESSURE SYSTEM CENTERED ABOUT 875 MILES WEST-SOUTHWEST
OF THE CAPE VERDE ISLANDS IS MOVING WESTWARD TO WEST-NORTHWESTWARD
AT 5 TO 10 MPH. SHOWER AND THUNDERSTORM ACTIVITY IS GRADUALLY
BECOMING BETTER ORGANIZED AND A TROPICAL DEPRESSION MAY BE FORMING.
IF THIS CURRENT DEVELOPMENT TREND CONTINUES...THEN ADVISORIES ON
THIS DISTURBANCE COULD BE INITIATED AS EARLY AS THIS AFTERNOON OR
EVENING. THERE IS A HIGH CHANCE...80 PERCENT...OF TROPICAL CYCLONE
FORMATION DURING THE NEXT 48 HOURS.
Based on the last of the visible satellite animations, it appears that the center is located at 10N 36W. Deep convection appears to be firing near or over the estimated center, and the aforementioned satellite animations depict that a closed surface circulation is rapidly trying to form, though this is not a particularly well-defined one as of yet. Also, upper-level outflow appears to be developing to the north and west of the system, but it is not well-defined as of yet. There is currently no outflow along the south and eastern sides of the circulation, which is to be expected due to competing influence from the ITCZ to the south, as well as moderate easterly to vertical wind shear that the system has been experiencing for the last couple of days.
However, this shear may be relaxing now over the estimated center position, based on low cloud motions indicated in various satellite animations as well as CIMSS wind shear analysis, which depicts only 5 kt of shear over the system, amidst a developing anticyclone aloft. As far as the track forecast is concerned, both CIMSS steering data and animation of water vapor imagery depict a gradual weakness developing in the Atlantic subtropical ridge to the north of the system. This weakness is being caused by a mid- to upper-level trough over the western Atlantic, and a developing upper-level low near 23N 61W that has recently pinched off from the trough. This weakness occurred a little sooner than I had expected this time yesterday, but nevertheless it is quite evident at this point.
It is because of this slight weakness that 91L has turned WNW this evening. Analysis of mid- to upper-level steering layers, along with data from the 18z GFS, indicates that this trough is not particularly well-defined, and more importantly, that the majority of the energy associated with this trough should remain far to the north of Invest 91L. This, along with the fact that the aforementioned upper low is forecast to gradually de-amplify and weaken, will not allow the subtropical ridge to weaken significantly over the next couple of days. Hence, 91L should continue moving toward the WNW over the next couple of days, with an increase in forward speed expected to begin over the next day or so.
This will allow 91L to gain some additional latitude and take greater advantage of the Coriolis force, producing greater cyclonic vorticity. By three days, the models unanimously forecast a rather large break to occur in the Atlantic subtropical ridge as another trough, located over the western United States, emerges into the western Atlantic.
My current thinking though, based on the current large-scale pattern across the United States, is that the overall strength of this trough is being vastly overestimated by the models. Even if it does end up being that powerful, I think it will lift out far faster than what most of the models are indicating this evening. I agree most strongly with the 12z ECMWF, and I expect more ridging than is currently being indicated by most of the models. This puts the greatest United States risk area at the east coast of Florida. However, this is a long-range forecast track, and as such, is highly uncertain. Nevertheless, residents along the east coast from Florida to North Carolina should carefully monitor the progress of this system over the next week or so.
First and foremost though, residents across the northern Leeward Islands, the Virgin Islands, and Puerto Rico, should closely monitor the progress of this system over the next several days, as the system could pass just north of that area in about four days.
Interestingly, the models are rather slow in developing this system, with only the CMC and ECMWF developing the system within the next two days. I have opted to go with these models, based on current organizational trends observed with Invest 91L. Upper-level winds favor additional development of this system, and the 18z GFS strengthens the aforementioned anticyclone, keeping it intact even as the system runs into strong westerly vertical shear associated with the TUTT north of the Leeward Islands in four days. This anticyclone may not allow much in the way of weakening when the system encounters shear from the TUTT.
Thereafter, as the system nears the western Atlantic, the upper air pattern is forecast to continue being zonal and unfavorable, with a positive twist: the GFS suggests that the anticyclone should begin to fade after four days. This would tend to weaken the system by day five as it approaches the western Atlantic. However, this shear is forecast to lift out relatively quickly, and it is not likely to completely destroy the system.
All in all, this system has developed much quicker than I thought it would. As such, I expect this system to become a tropical depression tonight or tomorrow morning. Again, residents across the northern Leeward Islands, the Virgin Islands and Puerto Rico, should closely monitor the progress of this system over the next several days.
Southwest Caribbean tropical wave
A tropical wave located a couple hundred miles east of the coast of Nicaragua continues to produce disorganized showers and thunderstorms. This system has become a little better organized this evening, owing to the long foreseen relaxation of the upper-level winds. However, proximity to land is expected to inhibit any significant development, and the system should move inland across Nicaragua sometime tomorrow morning. Regardless of development, locally heavy rainfall and strong gusty winds will overspread portions of Nicaragua, Honduras, Panama, El Salvador, and Costa Rica tonight and tomorrow.
Saturday, July 31, 2010
Tropical weather analysis - July 31, 2010
Eastern Atlantic tropical wave
A well-defined tropical wave located about 850 miles west-southwest of the Cape Verde Islands has become a little better organized this evening. Infrared satellite loops suggest that there is a rather concentrated area of deep convection along 8 to 9°N 32 to 33°W. There is also another area of active convection to the west of that, in the general vicinity of where ex-90L used to be.
A definite center is extremely difficult to locate tonight, even using shortwave infrared and RGB satellite animations. My best guess, which is highly uncertain, is 8N 32W. Although this system has become better organized this evening, the enormity of the cyclonic gyre with which it is embedded will likely keep any rapid consolidation to a minimum. All in all, based on CIMSS 850 mb vorticity data, this system is still poorly defined, and is embedded, as previously mentioned, in a large cyclonic gyre associated with an active ITCZ. Water vapor animations depict a large swath of very dry air just to the north of this complex weather disturbance, associated with the dry, dusty Saharan Air Layer that originates from the Sahara Desert of Africa, and gets periodically blown westward out into the Atlantic Ocean.
However, given the fact that the system will be moving generally W under the influence of a well-defined low- to mid-level tropospheric ridge, this dry air should not significantly impede development, since the steering flow will be primarily easterly, which will act to push the dry air away from the system. Latest CIMSS wind shear analysis indicates that the system is experiencing 10-20 kt of easterly to northeasterly shear, associated with a developing anticyclone just to the southwest of the Cape Verde Islands.
By about 36 hours, the system should start to gradually gain latitude and move WNW. Until then though, expect a continued W motion. By around 72 hours, a break in the Atlantic subtropical ridge is forecast to occur unanimously by all the models -- some keep it stronger, some weaker, but the general consensus is for at least a slight slackening of the south side of this ridge during this time, as a vigorous mid- to upper-level trough swings by across the mid-Atlantic states and New England.
There is still the possibility that the system could remain shallow and continue W, eventually entering the Caribbean. The NOGAPS keeps a stronger Bermuda-Azores high, which keeps the low-level flow generally easterly throughout the forecast period. This solution appears unlikely at this time, if not just for the fact that the system is likely to gradually deepen over the next couple of days.
The models are unanimously calling for tropical cyclogenesis from this feature, with the 12z CMC developing it east of the Leeward Islands in about four days. Interestingly, this particular model shows something of a Fujiwhara interaction between this system and another competing area of vorticity subsequent to this. This solution appears highly unlikely for now, but nevertheless the model has the right idea in developing this system. The 18z GFS indicates that cyclogenesis will occur right on the doorstep of the northern Leeward Islands in about four and a half days.
The 12z NOGAPS keeps the system weak, and as a consequence, it moves westward in tandem with the low-level easterly flow characteristic of the tropics. It develops it at 144 hours, while it is about 400 miles east of the central Leeward Islands. This model appears much too far south at this time, and hence I have discounted this track solution. But again, it does have the right idea with regards to eventual development from this system. Finally, the 12z ECMWF develops this system in about four days as it approaches the Leeward Islands.
Rather alarmingly, both the GFS and ECMWF foresee the synoptic scale pattern as being supportive of a stronger Atlantic subtropical ridge, strong enough to prevent the system from recurving harmlessly out to sea. While I do not like to speculate on long-range tracks, particularly with systems that do not even have a definite surface center, I am inclined to go with the solution provided by these models, based on the current large-scale pattern over North America.
Upper-level winds support continued slow development of this disturbance. I am not expecting any rapid development, however, and the NHC's current forecast of a 40% chance of tropical cyclogenesis occurring in 48 hours is a reasonable one. The earliest I would expect this system to become a tropical depression or tropical storm is Tuesday night, but more likely Wednesday afternoon.
Central Caribbean tropical wave
A tropical wave moving across the central Caribbean Sea continues to sporadically produce limited and disorganized shower activity. Upper-level winds are not conducive for development in this area, and are forecast to continue being largely zonal and strong, even as the system approaches Central America in about two days. I am not expecting any significant development of this wave, though it may bring heavy rains to Honduras, Nicaragua, El Salvador, and Costa Rica over the next couple of days as it continues moving generally W.
A well-defined tropical wave located about 850 miles west-southwest of the Cape Verde Islands has become a little better organized this evening. Infrared satellite loops suggest that there is a rather concentrated area of deep convection along 8 to 9°N 32 to 33°W. There is also another area of active convection to the west of that, in the general vicinity of where ex-90L used to be.
A definite center is extremely difficult to locate tonight, even using shortwave infrared and RGB satellite animations. My best guess, which is highly uncertain, is 8N 32W. Although this system has become better organized this evening, the enormity of the cyclonic gyre with which it is embedded will likely keep any rapid consolidation to a minimum. All in all, based on CIMSS 850 mb vorticity data, this system is still poorly defined, and is embedded, as previously mentioned, in a large cyclonic gyre associated with an active ITCZ. Water vapor animations depict a large swath of very dry air just to the north of this complex weather disturbance, associated with the dry, dusty Saharan Air Layer that originates from the Sahara Desert of Africa, and gets periodically blown westward out into the Atlantic Ocean.
However, given the fact that the system will be moving generally W under the influence of a well-defined low- to mid-level tropospheric ridge, this dry air should not significantly impede development, since the steering flow will be primarily easterly, which will act to push the dry air away from the system. Latest CIMSS wind shear analysis indicates that the system is experiencing 10-20 kt of easterly to northeasterly shear, associated with a developing anticyclone just to the southwest of the Cape Verde Islands.
By about 36 hours, the system should start to gradually gain latitude and move WNW. Until then though, expect a continued W motion. By around 72 hours, a break in the Atlantic subtropical ridge is forecast to occur unanimously by all the models -- some keep it stronger, some weaker, but the general consensus is for at least a slight slackening of the south side of this ridge during this time, as a vigorous mid- to upper-level trough swings by across the mid-Atlantic states and New England.
There is still the possibility that the system could remain shallow and continue W, eventually entering the Caribbean. The NOGAPS keeps a stronger Bermuda-Azores high, which keeps the low-level flow generally easterly throughout the forecast period. This solution appears unlikely at this time, if not just for the fact that the system is likely to gradually deepen over the next couple of days.
The models are unanimously calling for tropical cyclogenesis from this feature, with the 12z CMC developing it east of the Leeward Islands in about four days. Interestingly, this particular model shows something of a Fujiwhara interaction between this system and another competing area of vorticity subsequent to this. This solution appears highly unlikely for now, but nevertheless the model has the right idea in developing this system. The 18z GFS indicates that cyclogenesis will occur right on the doorstep of the northern Leeward Islands in about four and a half days.
The 12z NOGAPS keeps the system weak, and as a consequence, it moves westward in tandem with the low-level easterly flow characteristic of the tropics. It develops it at 144 hours, while it is about 400 miles east of the central Leeward Islands. This model appears much too far south at this time, and hence I have discounted this track solution. But again, it does have the right idea with regards to eventual development from this system. Finally, the 12z ECMWF develops this system in about four days as it approaches the Leeward Islands.
Rather alarmingly, both the GFS and ECMWF foresee the synoptic scale pattern as being supportive of a stronger Atlantic subtropical ridge, strong enough to prevent the system from recurving harmlessly out to sea. While I do not like to speculate on long-range tracks, particularly with systems that do not even have a definite surface center, I am inclined to go with the solution provided by these models, based on the current large-scale pattern over North America.
Upper-level winds support continued slow development of this disturbance. I am not expecting any rapid development, however, and the NHC's current forecast of a 40% chance of tropical cyclogenesis occurring in 48 hours is a reasonable one. The earliest I would expect this system to become a tropical depression or tropical storm is Tuesday night, but more likely Wednesday afternoon.
Central Caribbean tropical wave
A tropical wave moving across the central Caribbean Sea continues to sporadically produce limited and disorganized shower activity. Upper-level winds are not conducive for development in this area, and are forecast to continue being largely zonal and strong, even as the system approaches Central America in about two days. I am not expecting any significant development of this wave, though it may bring heavy rains to Honduras, Nicaragua, El Salvador, and Costa Rica over the next couple of days as it continues moving generally W.
Friday, July 30, 2010
Tropical weather analysis - July 30, 2010
Invest 90L
A strong tropical wave, dubbed "Invest 90L" by the National Hurricane Center, has become less organized throughout today. This isn't due to unfavorable atmospheric conditions. Rather, it is due to interaction with a larger tropical wave to the east, near the Cape Verde Islands. I suspect that this wave will continue to gradually ingest Invest 90L, and will likely be designated "Invest 91L" tomorrow morning. This system is very poorly organized, with shortwave infrared satellite animations indicating very little in the way of shower activity, much less any cyclonic vorticity. I can detect a faint, very weak and rapidly dissipating spin from 8 to 9°N and along 34 to 32°W. The rest of the convection in the area is associated primarily with the ITCZ, not the wave.
Latest CIMSS wind shear analysis from University of Wisconsin CIMSS depicts only 5-10 kt of northeasterly shear impinging upon the system. However, again, because of dangerously close proximity to the aforementioned tropical wave to the east, I am not expecting significant development of Invest 90L. Obviously though, it would be rather foolhardy for anyone to take their eyes off the system until the system completely loses its identity.
The Cape Verde wave should move W over the next couple of days, with a more WNW motion occurring in 60-72 hours as a shortwave trough weakens the ridge to the north. This system may pass north of the Leeward Islands and Puerto Rico in about five to seven days, but it is uncertain if this system will be able to recurve out to sea entirely. This system may be a long-range threat to the southeast or northeastern United States, but this is highly speculative, and residents living in those areas should not be overly concerned. Upper-level winds favor development over the next several days, but as the wave approaches the Lesser Antilles, strong westerly shear associated with the TUTT will return once again, which will make additional development or intensification highly improbable, and the system may even destroyed at that point.
Should it remain farther south, however, and enter the Caribbean, upper-level winds greatly favor intensification.
Eastern Caribbean tropical wave
A tropical wave located across the eastern Caribbean Sea continues to produce disorganized convection. Upper-level winds are currently unfavorable for development. This, along with the wave's fast forward speed, 20 to 25 mph (which is expected to continue for the next couple days, by the way), should prevent any appreciable organization from occurring until the system nears Central America in about two to three days. At that point, upper-level winds will also relax, and the system will have a small window of opportunity in which to become a tropical cyclone. I am not expecting this to happen, however.
Also, I still fully anticipate an active season. I cannot stress this enough. This season will be active -- in 1998, the most similar year to this one that I can find, the second named storm did not occur until August 20. That season ended up producing 14 named storms, 10 hurricanes, and 3 major hurricanes, and, most remarkably, four simultaneous hurricanes existed in the basin on September 25 -- Georges, Ivan, Jeanne, and Karl. The season also had three hurricanes impact the United States mainland: Bonnie, Earl, and Georges.
Lastly, it featured the mighty Hurricane Mitch, which killed anywhere from 11 to 20,000 people across portions of Central America due to days of prolonged torrential rainfall, which produced flash flooding and mudslides across mountainous areas.
While I'm not saying we're necessarily going to see an exact repeat of 1998, I do not want anyone to be foolish enough to drop their guard by thinking that the season is over. Most parameters still point to a sharp upswing in overall activity beginning the second week of August.
A strong tropical wave, dubbed "Invest 90L" by the National Hurricane Center, has become less organized throughout today. This isn't due to unfavorable atmospheric conditions. Rather, it is due to interaction with a larger tropical wave to the east, near the Cape Verde Islands. I suspect that this wave will continue to gradually ingest Invest 90L, and will likely be designated "Invest 91L" tomorrow morning. This system is very poorly organized, with shortwave infrared satellite animations indicating very little in the way of shower activity, much less any cyclonic vorticity. I can detect a faint, very weak and rapidly dissipating spin from 8 to 9°N and along 34 to 32°W. The rest of the convection in the area is associated primarily with the ITCZ, not the wave.
Latest CIMSS wind shear analysis from University of Wisconsin CIMSS depicts only 5-10 kt of northeasterly shear impinging upon the system. However, again, because of dangerously close proximity to the aforementioned tropical wave to the east, I am not expecting significant development of Invest 90L. Obviously though, it would be rather foolhardy for anyone to take their eyes off the system until the system completely loses its identity.
The Cape Verde wave should move W over the next couple of days, with a more WNW motion occurring in 60-72 hours as a shortwave trough weakens the ridge to the north. This system may pass north of the Leeward Islands and Puerto Rico in about five to seven days, but it is uncertain if this system will be able to recurve out to sea entirely. This system may be a long-range threat to the southeast or northeastern United States, but this is highly speculative, and residents living in those areas should not be overly concerned. Upper-level winds favor development over the next several days, but as the wave approaches the Lesser Antilles, strong westerly shear associated with the TUTT will return once again, which will make additional development or intensification highly improbable, and the system may even destroyed at that point.
Should it remain farther south, however, and enter the Caribbean, upper-level winds greatly favor intensification.
Eastern Caribbean tropical wave
A tropical wave located across the eastern Caribbean Sea continues to produce disorganized convection. Upper-level winds are currently unfavorable for development. This, along with the wave's fast forward speed, 20 to 25 mph (which is expected to continue for the next couple days, by the way), should prevent any appreciable organization from occurring until the system nears Central America in about two to three days. At that point, upper-level winds will also relax, and the system will have a small window of opportunity in which to become a tropical cyclone. I am not expecting this to happen, however.
Also, I still fully anticipate an active season. I cannot stress this enough. This season will be active -- in 1998, the most similar year to this one that I can find, the second named storm did not occur until August 20. That season ended up producing 14 named storms, 10 hurricanes, and 3 major hurricanes, and, most remarkably, four simultaneous hurricanes existed in the basin on September 25 -- Georges, Ivan, Jeanne, and Karl. The season also had three hurricanes impact the United States mainland: Bonnie, Earl, and Georges.
Lastly, it featured the mighty Hurricane Mitch, which killed anywhere from 11 to 20,000 people across portions of Central America due to days of prolonged torrential rainfall, which produced flash flooding and mudslides across mountainous areas.
While I'm not saying we're necessarily going to see an exact repeat of 1998, I do not want anyone to be foolish enough to drop their guard by thinking that the season is over. Most parameters still point to a sharp upswing in overall activity beginning the second week of August.
Thursday, July 29, 2010
Tropical weather analysis - July 29, 2010
Invest 90L
A large but well-defined perturbation in the Intertropical Convergence Zone (ITCZ) was designated Invest 90L this afternoon by the National Hurricane Center. Visible satellite animations suggest that this system is embedded within a large area of convection and cyclonic vorticity associated with the ITCZ. My best estimate for a "center" position, based on satellite data, is 7N 31W. Latest CIMSS 850 mb vorticity data also somewhat supports this.
Upper-level winds are favorable for additional development of this system, with CIMSS wind shear analysis indicating only 5-10 kt of east to northeasterly shear over the system. This favorable upper-level environment is forecast to persist throughout the next several days, with a fairly uniform easterly flow. The two largest impediments I can see for 90L is the large amount of dry air to the north, depicted rather nicely on water vapor loops, and the broad cyclonic gyre that the system is embedded in. However, given the very moist environment within the vicinity of the disturbance, along with the fact that the system should move generally W over the next couple of days, I am not expecting the dry air to completely halt any additional development of 90L.
Analysis of 12z steering from PSU's e-wall suggests that a break in the Atlantic subtropical ridge could occur in about 60-72 hours as a mid- to upper-level trough swings by to the north of the system. However, unless 90L develops significantly during the next three days, this weakness should not be strong enough to turn the system poleward so much so that it completely misses any and all land areas.
All of that having been said, I expect some slow additional development of the disturbance as it moves generally W over the next couple of days. As previously noted, a turn to the WNW could occur in 60-72 hours as the subtropical ridge weakens somewhat. The 18z GFS develops this system just north of Puerto Rico in 168 hours. The 12z CMC develops this in as little as two and a half to three days, and eventually makes it a hurricane. However, such rapid development does not appear likely at this time, and I am discounting both the track and intensity solution currently being provided by this model. Finally, the 12z ECMWF hints at tropical cyclogenesis occurring north of the Leeward Islands in about six days, but quickly loses the system as it moves it WNW toward the southeast United States coast.
I would not expect development to begin occurring in earnest until around 60 hours, as the system begins to gain some latitude. The National Hurricane Center is giving 90L a 20% chance of becoming a tropical cyclone within the next 48 hours, and this is a reasonable forecast.
Windward Islands tropical wave
A tropical wave is producing scattered showers and thunderstorms across portions of the Windward Islands and adjacent eastern Caribbean Sea.
However, the wave axis has not yet passed these islands. Upper-level winds are currently not favorable for development, but could become more favorable over the next several days as the wave moves generally W, well-embedded within the low-level easterly trade wind flow common of the tropics. Surface observations from the Windward Islands, along with buoy data, indicate that nothing of note is occurring at the surface in association with this wave.
I suspect that any development will be very slow to occur. And, though the upper wind flow may improve somewhat over the next several days, the system will run into Central America in about four to five days.
Regardless of development, locally heavy rainfall and strong gusty winds will accompany the wave as it passes through the Windward Islands tonight. None of the models, save the CMC, which is always too bullish with tropical cyclogenesis, significantly develop the wave.
A large but well-defined perturbation in the Intertropical Convergence Zone (ITCZ) was designated Invest 90L this afternoon by the National Hurricane Center. Visible satellite animations suggest that this system is embedded within a large area of convection and cyclonic vorticity associated with the ITCZ. My best estimate for a "center" position, based on satellite data, is 7N 31W. Latest CIMSS 850 mb vorticity data also somewhat supports this.
Upper-level winds are favorable for additional development of this system, with CIMSS wind shear analysis indicating only 5-10 kt of east to northeasterly shear over the system. This favorable upper-level environment is forecast to persist throughout the next several days, with a fairly uniform easterly flow. The two largest impediments I can see for 90L is the large amount of dry air to the north, depicted rather nicely on water vapor loops, and the broad cyclonic gyre that the system is embedded in. However, given the very moist environment within the vicinity of the disturbance, along with the fact that the system should move generally W over the next couple of days, I am not expecting the dry air to completely halt any additional development of 90L.
Analysis of 12z steering from PSU's e-wall suggests that a break in the Atlantic subtropical ridge could occur in about 60-72 hours as a mid- to upper-level trough swings by to the north of the system. However, unless 90L develops significantly during the next three days, this weakness should not be strong enough to turn the system poleward so much so that it completely misses any and all land areas.
All of that having been said, I expect some slow additional development of the disturbance as it moves generally W over the next couple of days. As previously noted, a turn to the WNW could occur in 60-72 hours as the subtropical ridge weakens somewhat. The 18z GFS develops this system just north of Puerto Rico in 168 hours. The 12z CMC develops this in as little as two and a half to three days, and eventually makes it a hurricane. However, such rapid development does not appear likely at this time, and I am discounting both the track and intensity solution currently being provided by this model. Finally, the 12z ECMWF hints at tropical cyclogenesis occurring north of the Leeward Islands in about six days, but quickly loses the system as it moves it WNW toward the southeast United States coast.
I would not expect development to begin occurring in earnest until around 60 hours, as the system begins to gain some latitude. The National Hurricane Center is giving 90L a 20% chance of becoming a tropical cyclone within the next 48 hours, and this is a reasonable forecast.
Windward Islands tropical wave
A tropical wave is producing scattered showers and thunderstorms across portions of the Windward Islands and adjacent eastern Caribbean Sea.
However, the wave axis has not yet passed these islands. Upper-level winds are currently not favorable for development, but could become more favorable over the next several days as the wave moves generally W, well-embedded within the low-level easterly trade wind flow common of the tropics. Surface observations from the Windward Islands, along with buoy data, indicate that nothing of note is occurring at the surface in association with this wave.
I suspect that any development will be very slow to occur. And, though the upper wind flow may improve somewhat over the next several days, the system will run into Central America in about four to five days.
Regardless of development, locally heavy rainfall and strong gusty winds will accompany the wave as it passes through the Windward Islands tonight. None of the models, save the CMC, which is always too bullish with tropical cyclogenesis, significantly develop the wave.
Monday, July 26, 2010
Louisiana hurricane history Part 3b: Unnamed hurricane (Sep 11 - Sep 16)
This storm was the second in a series of three powerful hurricanes to make landfall in southeastern Louisiana during the 1860 Atlantic hurricane season. This system was first noted in the early morning hours of September 11 about 150 miles west-northwest of the Dry Tortugas. It made landfall on the morning of September 16 near the Mouth of the Mississippi River along the southwest end of Plaquemines Parish.
Storm history
As mentioned above, a Category 2 hurricane was first detected about 150 miles west-northwest of the Dry Tortugas near the Florida Keys, moving W. As with most systems in the 1800s, the complete history of this hurricane is not known. It is possible that the system moved in from the Bahamas and south Florida, but this presents a problem: why was such an impact not recorded, even during those technologically scarce times? The only possible explanation to this is that the system was only a tropical depression or tropical storm whilst traversing these regions, and it did not intensify significantly until it reached the eastern Gulf of Mexico. At that point though, rapid intensification would have had to have occurred in order for the storm to go from a tropical depression/storm to a Category 2 hurricane within the span of just a day or so. Another possibility is that the system was moving northward from the western Caribbean, across western Cuba, and then into the Gulf of Mexico before a ridge built back in to the north. However, this would be a rather atypical motion for the middle of September, and in fact, more typical of the middle of October.
Regardless of its origin, the hurricane continued generally westward as a Category 2 until the morning of September 12, at which point it turned to the west-northwest as the subtropical ridge to the north weakened somewhat, likely due to the approach of a mid-latitude trough from the west. The hurricane turned to the northwest late on the afternoon of September 13 as it encountered a further weakness in the aforementioned ridge. Around 24 hours later, the hurricane turned northward, now well-embedded within the southerly flow along the western periphery of the subtropical ridge, and the aforementioned trough and its associated cold front to the west. The hurricane made landfall across lower Plaquemines Parish at 0600 GMT September 15, then turned further poleward, to the north-northeast, at around 1200 GMT that same day. At this time, the hurricane is still estimated to have been a Category 2, located just offshore the southwestern coast of Mississippi. The hurricane quickly made a second landfall near Bay St. Louis, still a Category 2.
The hurricane continued north-northeastward under the influence from the trough, and ultimately dissipated somewhere over the eastern United States. It was last identified as a 45 kt (50 mph) tropical storm at 0600 GMT near 33.0°N 88.0°W, still moving quickly north-northeastward under the influence of the climatological mid-latitude westerlies.
Figure 1. Track of the hurricane.
Louisiana
Gale force winds were reported for around 20 hours across extreme southeast Louisiana as the hurricane ravaged the area. Additionally, and quite rare in a tropical cyclone, hail was reported. The only other tropical cyclone I can think of that has produced hail (though there were undoubtedly others as well) is 1995's Hurricane Marilyn.
Every building in Balize, an old settlement located about five miles from Pillottown, (the latter of which is located along extreme lower Plaquemines Parish, on the southeast side facing the Gulf), was destroyed by the hurricane, and the third Bayou St. John lighthouse was damaged beyond repair.
A storm surge in excess of several feet was reported across lower Plaquemines Parish, which inundated the area and killed several people. The tied was reported as being six feet above the high tide. All wharves along the southern shore of Lake Pontchartrain were destroyed.
Mississippi
Across Mississippi, where the hurricane's second landfall occurred, a lighthouse in the area, along with a hotel, were swept away by the storm surge.
Total damages from the hurricane exceeded $1 million.
Storm history
As mentioned above, a Category 2 hurricane was first detected about 150 miles west-northwest of the Dry Tortugas near the Florida Keys, moving W. As with most systems in the 1800s, the complete history of this hurricane is not known. It is possible that the system moved in from the Bahamas and south Florida, but this presents a problem: why was such an impact not recorded, even during those technologically scarce times? The only possible explanation to this is that the system was only a tropical depression or tropical storm whilst traversing these regions, and it did not intensify significantly until it reached the eastern Gulf of Mexico. At that point though, rapid intensification would have had to have occurred in order for the storm to go from a tropical depression/storm to a Category 2 hurricane within the span of just a day or so. Another possibility is that the system was moving northward from the western Caribbean, across western Cuba, and then into the Gulf of Mexico before a ridge built back in to the north. However, this would be a rather atypical motion for the middle of September, and in fact, more typical of the middle of October.
Regardless of its origin, the hurricane continued generally westward as a Category 2 until the morning of September 12, at which point it turned to the west-northwest as the subtropical ridge to the north weakened somewhat, likely due to the approach of a mid-latitude trough from the west. The hurricane turned to the northwest late on the afternoon of September 13 as it encountered a further weakness in the aforementioned ridge. Around 24 hours later, the hurricane turned northward, now well-embedded within the southerly flow along the western periphery of the subtropical ridge, and the aforementioned trough and its associated cold front to the west. The hurricane made landfall across lower Plaquemines Parish at 0600 GMT September 15, then turned further poleward, to the north-northeast, at around 1200 GMT that same day. At this time, the hurricane is still estimated to have been a Category 2, located just offshore the southwestern coast of Mississippi. The hurricane quickly made a second landfall near Bay St. Louis, still a Category 2.
The hurricane continued north-northeastward under the influence from the trough, and ultimately dissipated somewhere over the eastern United States. It was last identified as a 45 kt (50 mph) tropical storm at 0600 GMT near 33.0°N 88.0°W, still moving quickly north-northeastward under the influence of the climatological mid-latitude westerlies.
Figure 1. Track of the hurricane.
Louisiana
Gale force winds were reported for around 20 hours across extreme southeast Louisiana as the hurricane ravaged the area. Additionally, and quite rare in a tropical cyclone, hail was reported. The only other tropical cyclone I can think of that has produced hail (though there were undoubtedly others as well) is 1995's Hurricane Marilyn.
Every building in Balize, an old settlement located about five miles from Pillottown, (the latter of which is located along extreme lower Plaquemines Parish, on the southeast side facing the Gulf), was destroyed by the hurricane, and the third Bayou St. John lighthouse was damaged beyond repair.
A storm surge in excess of several feet was reported across lower Plaquemines Parish, which inundated the area and killed several people. The tied was reported as being six feet above the high tide. All wharves along the southern shore of Lake Pontchartrain were destroyed.
Mississippi
Across Mississippi, where the hurricane's second landfall occurred, a lighthouse in the area, along with a hotel, were swept away by the storm surge.
Total damages from the hurricane exceeded $1 million.
Subscribe to:
Posts (Atom)