Tropical weather analysis - June 27, 2010 - second edition

Began writing at approximately 7:47 PM EDT

Alex weakened to a tropical depression this morning during its prolonged passage over Belize and the Yucatan Peninsula. As of the 4:00 PM CDT advisory from the National Hurricane Center, Alex's center was estimated to be near 19.2N 90.9W, moving WNW at 9 mph. Maximum sustained winds were 30 kt (35 mph), and the central pressure 999 mb. Visible satellite loops show that Alex has continued moving WNW since the issuance of the previous advisory, and is now located just inland from the western Yucatan Peninsula, and is ready to emerge into the Bay of Campeche around 60 miles southwest Campeche, Mexico. Alex should begin moving NW very soon, as CIMSS steering as well as water vapor animations suggest that a weakness is evident within the subtropical ridge around 89W.

It will be interesting to see how Alex responds to this weakness over the next several hours. So far, no northwesterly component of motion has been observed with Alex. However, I am nonetheless expecting a NW to NNW motion to begin soon, persisting for the next 6-12 hours, after which point it should once again commit to a more westward track.

The biggest question regarding Alex continues to be track, not intensity, since the latter is fairly straightforward in this case. The models agree on Alex moving only very slowly across the Bay of Campeche for the first couple of days, owing to a weak steering regime imparted by a vigorous longwave trough currently stretching from the high plains all the way to the southwestern United States. There is some southwesterly mid to upper flow already evident across the northwestern Gulf of Mexico, as per water vapor loops. However, this flow appears to be quite weak at the moment, and is not enough to fully erode the ridge so that Alex gains a significant amount of latitude, at least in the near-term (again, I expect a NW to NNW motion for the next 6-12 hours, followed by a more westerly component after that, albeit slowly).

At the moment, it is difficult to assess the likely evolution of the aforementioned trough beyond, say, 24 hours. Thus, I will hold off on doing so. Instead, I will split difference between the various models, which all foresee Alex moving painfully slowly across the Bay of Campeche, particularly after 24 hours, with a more solid steering regime influencing the cyclone beginning in about 60 to 72 hours. Where they differ, obviously, is whether or not the trough or the ridge will steer Alex to its final landfall during this time.

Again, it's not easy to tell at this point which solution will be correct. Were I to hazard a guess though, based on water vapor imagery alone, it would be that the GFS and CMC continue to be much too poleward, particularly the latter, which depicts as a landfall in western Louisiana. Instead, I will split the difference between the various models and forecast a landfall along the south-central Texas coast. I am in best agreement with the 18z HWRF, track-wise. Should this forecast end up being correct, Corpus Christi would be under the gun for a possible direct hit from then Hurricane Alex.

However, the forecast is highly uncertain at this time, and is subject to change. The threat to Brownsville southward to Tampico is not really minimized at present, so residents there need not let their guard down. Given the large amount of uncertainty in this forecast, residents from Tampico, Mexico to Cameron, Louisiana should closely monitor the progress of Alex over the next several days.

The intensity forecast, as I said, is much simpler. The GFS, which has performed exceptionally well with the evolution of the anticyclone, continues to depict an anticyclonic environment across the western Gulf of Mexico. And, although the aforementioned anticyclone is not directly atop Alex at the moment, the GFS brings it to the vicinity of the cyclone within about 24 hours. Given the fact that the anticyclone is not currently centered over Alex, the fact that TCHP is very low off the immediate coast of the western Yucatan Peninsula, as well as the fact that it typically takes a cyclone at least 24 hours to recover its inner core after prolonged passage overland, I am not expecting significant intensification of Alex over the next day or so, and any abrupt intensification of the cyclone during this time will be from the winds catching up to the already very low central pressure.

Thereafter, as Alex moves underneath the anticyclone and into warmer waters, more steady, possibly rapid intensification appears to be in order, under a light upper-level wind flow. The timing of landfall is not completely certain, but is generally agreed by the models to be sometime on Thursday morning. Hence, I will forecast a landfall of Alex on Thursday morning. I do not want to deviate to a more poleward track just yet, at least until I see how the trough continues to unfold.

I expect Alex to be at hurricane intensity at landfall, and it could even be a Category 2. A Category 3 is even possible, but the likelihood of this happening appears rather slim at the moment.