Tropical weather analysis - June 27, 2010

Tropical Storm Alex made landfall just north of Belize City, Belize as a 55 kt (65 mph) tropical storm early this evening. At the time of landfall, Alex appeared to be organizing into a hurricane, with a warm spot evident within the midst of the well-defined central dense overcast (CDO). As per the 10:00 PM CDT advisory from the National Hurricane Center, Alex was centered near 17.7N 88.4W, moving WNW at 12 mph, had maximum sustained winds of 50 kt (60 mph), and a pressure of 997 mb. Alex still appears to be moving WNW at this present time, though at the time of this analysis I place the center at 17N 89W, as opposed to 88W. Not because the NHC was wrong, but because the system has since moved a bit farther inland. Based on steering currents from CIMSS, I foresee Alex moving NW very soon, steered by southeasterly flow along the southwestern periphery of a persistent ridge.

Obviously, the longer Alex moves WNW, the more land it will encounter, and the weaker it will be when it emerges into the southern Gulf of Mexico in a couple of days. Alex should emerge into the southern Gulf of Mexico in about 30 hours, but not before bringing flooding rains to Belize and portions of the Yucatan Peninsula. Though I mentioned yesterday that Alex could simply dissipate over the Yucatan, I am not expecting that to happen at this time, even if it's passing over some more rugged terrain than was previously forecast. Why? Because Alex is an exceptionally large storm, has a well-defined anticyclonic outflow pattern aloft, and abundant convection. Large systems take considerable time to wind down. Thereafter, models are widely divergent -- much more so than they were this time yesterday.

As per 18z, the GFS and GFDL both bring the system into Texas, with the GFS taking Alex to the central Texas coast in 168 hours, and the GFDL to the upper Texas coast as a Category 3 in just under five days. As per 12z (still awaiting the 0z run), the CMC is mimicking the GFS, albeit slightly farther south, and at a much earlier time -- around 108 hours.

The HWRF, NOGAPS, UKMET, and ECMWF all bring the system into central Mexico in about three to four days. Given the weak steering flow expected across that portion of the Gulf expected across the southern Gulf from 36 to at least 72 hours, I tend to lean toward a landfall on late Wednesday or early Thursday. There is still considerable uncertainty as to where Alex will ultimately make its second landfall, as I displayed above (with the two divergent model camps). The key player in this scenario will be an upper-level trough, analyzed very well on water vapor loops. It does appear that this trough is dipping quite far to the south -- much farther than the models were indicating this time yesterday. Because of this, it is possible that Alex gains some latitude after emerging into the Bay of Campeche in about 30 hours. How much latitude, obviously, will depend upon the evolution of the aforementioned upper trough.

A stronger Alex would be more inclined to respond to the trough by moving poleward, while a weaker cyclone would be more inclined to stall until the trough bypasses it to the north, and the ridge rebuilds in the wake of the trough. I do not think, however, that Alex will gain enough latitude to appreciably affect the oil spill region, and will probably not even as gain as much latitude as the 18z GFDL is predicting.

I will not forecast a significant increase in latitude at this time, however, since it remains to be seen just how the trough will evolve and how strong Alex will be within 30 hours or so -- the time it is expected to arrive within the Bay of Campeche. Given the greater than normal uncertainty in this forecast, residents from Veracruz to Houston should carefully monitor the progress of Alex over the next several days (though I place less emphasis on Houston than points farther south along the Texas coast -- but just as a precautionary measure). At this time, I will go with the NHC's forecast, albeit slightly farther north.

It should also be noted that Alex is a large circulation. Because of this, the farther north Alex makes its final landfall, the more energy will be pulled eastward -- it will have a lot of energy to work with, even after dissipation -- large systems do not die easily. Hence, heavy, possibly flooding rainfall, will be possible across portions of Texas and Louisiana even after dissipation of Alex as a tropical cyclone -- provided, of course, it gains some unforeseen (by the NHC) latitude. Even if not, the western half of Texas will certainly see some remnant moisture from this system.

As far as intensity goes, I agree pretty well with the NHC's current thinking, bringing the system to hurricane status within 72 hours. It typically takes around 24 hours for a tropical cyclone to reorganize its inner core after prolonged passage overland. Hence, I do not foresee significant intensification of Alex for the first 24 hours after emergence into the Bay of Campeche. The intensity forecast isn't as clear cut as I might have made it seem, however, because the GFS and ECMWF are still divided on the vertical shear forecast, and also because Alex's ultimate final landfall location is still uncertain at this point.

The GFS keeps a strongly anticyclonic environment across the western and west-central Gulf of Mexico, which would obviously favor intensification. The ECMWF, on the other hand, while lifting the shear out of the southwestern Gulf, still keeps some shear across the western and west-central Gulf, and a largely zonal flow, to boot. This would greatly hamper intensification of Alex. However, given that the GFS seems to be the more reliable model with shear profiles, particularly lately, I will go with it and forecast strengthening as Alex emerges into the Bay of Campeche.

How much depends not only track, but on the timing of landfall, as well. I have delayed the system's landfall a bit, in comparison to the NHC, however, and I expect a landfall on late Wednesday night. This forecast will have to be adjusted accordingly as we witness the evolution and progression of the upper trough. So the later Alex comes in, the greater chance it will have to intensify.

Also of note is the TCHP, which, as per the graph above, is quite high across the western Gulf of Mexico, certainly enough to generate a Category 2 hurricane, provided upper-level conditions allow, of course. Should Alex move farther north than forecast, it will have a chance to intensify more than is currently forecast by me or the NHC. Given the uncertainty, however, I'll only go with a minimal hurricane within 72 hours, and an intensifying Category 1 at landfall, which I expect to occur a bit to the north of Tampico, Mexico.