Tropical weather analysis - July 5, 2010

Invest 95L

Invest 95L has recently moved inland between Morgan City and Houma, Louisiana. This is suggested by shortwave infrared satellite animations, along with doppler radar animations from Slidell, Louisiana. 95L appeared to be on the verge of becoming a tropical depression in the several hours prior to landfall, with both doppler radar and satellite animations suggesting increased organization, including the formation of low-level spiral banding.

Based on radar and satellite data, I assume that the surface center is located at 29N 91W, and moving slowly to the NW. This general motion should continue for at least the next 12-18 hours. Thereafter, the system should turn N and NE ahead of a mid-latitude trough in the westerlies. The main threat from this system is heavy rainfall, which could be in excess of 1 to 3 inches per hour right near the center. In the last 24 hours, as much as 6 inches of rain has fallen about 75 miles south of Houma right near the core of the storm.

The other impact from 95L will be sustained winds in excess of 25 to 30 mph right near the center, with gusts up to tropical storm force. These winds could blow around unsecured objects, as well as down small trees. Heavy rains in excess of 1 to 3 inches, with locally higher amounts could overspread portions of central and southeastern Louisiana over the next 12-18 hours. These rains could produce some localized flooding in some areas.

This will be my final mention of Invest 95L.

Invest 96L

Invest 96L, located across the extreme western Caribbean Sea, continues to be a far greater threat than any other area in the Atlantic, at least immediately speaking (there are other areas of interest, which I'll get to in a bit), and all in all, I feel this has a good chance of developing into the season's second named storm.

The center isn't especially easy to locate, but based on animation of shortwave infrared satellite imagery, I put it near 20N 86W. Surface pressures, while somewhat low, are not overly so, and have actually been somewhat rising over the last several hours (though some areas have seen nearly steady-state surface pressures). Surface and buoy observations are not currently suggesting anything resembling a closed surface circulation. Unfortunately, ASCAT completely missed the disturbance, as is usually the case, so we cannot ascertain just how much of a surface signature is associated with this feature, if there is any at all. CIMSS analysis depicts 20 kt of northwesterly shear impinging upon the estimated center of the system.

This shear is associated with a small but well-defined upper-level anticyclone currently centered across the northeastern portion of the Yucatan Peninsula. 96L appears to be moving NW at 10 to 15 kt, under the influence of a weak low- and mid-level ridge. The system is not presently stacked in the vertical, with a noticeable southeastward tilt of the 850 mb and 700 mb vorticity centers.

I am not expecting any significant development of 96L for at least the next day or so. It should enter the southern Gulf of Mexico within the next several hours. The 18z GFS does not call for a significantly anticyclonic environment across the Gulf of Mexico as it did at this time yesterday. In fact, the upper wind environment might well be a zonal one until after 24 hours. So, although upper-level winds do appear conducive enough for at least some slow development, it is not looking as favorable as it was this time yesterday. However, SSTs are plenty warm, and the warm water extends to a moderate depth.

There is a heat eddy in the south-central Gulf of Mexico from 24N-25N and 87W-88W. Should 96L pass over this heat eddy (which is possible, particularly the extreme western edge of the eddy), it could find enough heat energy to rapidly transition to a tropical cyclone. There is also a noticeable, much larger swath of heat from 96W to 91W and from 25N to 28N. This will also provide the system with additional heat energy. All in all, I expect this system to become a tropical depression within the next 48 hours, though it could occur somewhat sooner if the system becomes significantly better organized during the day tomorrow. Regardless of development, locally heavy rainfall will overspread portions of the Yucatan Peninsula, western Cuba, and the Cayman Islands over the 12 hours or so, and then the Florida Keys after that.

The majority of the models take the system into southeastern Texas in about 48-54 hours, though none of them are showing the system as being particularly strong. This may be an indication (more like a compliment, actually) that the upper-level environment will not be as favorable as previously thought. However, I don't see anything within the upper-level environment to keep this system as weak as most of the models are forecasting. Only the SHIPS significantly intensifies the system, bringing it to just under hurricane status in 72 hours. The other models, save the ECMWF, are much quicker in bringing the system inland, so the SHIPS does look suspect. The reliable ECMWF is also a late landfall model, forecasting the system to be inland by 72 hours, rather than at 48-54 hours as the general consensus predicts.

However, the ECMWF also looks suspect, because it's much too far south, bringing the system inland near Port Mansfield. I have opted to discount this scenario for now, and instead forecast a southeast Texas landfall at around 60 hours. The biggest reason this system may not be as powerful as previously thought is that it has very little time to get its act together before it moves inland. Nevertheless, residents across the western Caribbean and the Gulf of Mexico should carefully monitor the progress of this system over the next couple of days. I expect that this system will become a moderate tropical storm, and possibly a minimal hurricane.

Eastern Caribbean tropical wave

A tropical wave located in the eastern Caribbean Sea is interacting with an upper-level trough and generating a large area of cloudiness and showers across the eastern Caribbean and adjacent Windward Islands. Upper-level winds are currently unfavorable for development, but are forecast to become more conducive as the system moves to the WNW at around 15 kt over the next several days. None of the computer models are currently developing this wave, but it bears watching, given that the upper environment could improve over the next couple days (though the general flow looks to remain largely zonal at this point).

Bahamas disturbance

Another disturbance is located over the Bahamas, and is associated with a cold front. Upper-level winds are not currently favorable for development, though they are forecast to improve gradually over the next several days as the system moves little. All in all though, this area is rather unimpressive at the moment, and I suspect that any development will be very slow to occur. The CMC and GFS (operational) are hinting at development of this system in about four days, though they show it, fortunately, recurving out to sea ahead of an upper-level trough. The NOGAPS keeps the ridge stronger, however, which would force the system on a W track into the Gulf of Mexico.