11 PM ALEX UPDATE

11 PM UPDATE TRACK PREDICTION

An Air Force Reserve unit aircraft has been investigating Alex this evening and measured a minimum pressure of 991 mb and peak flight-level winds of 42 kt north of the center. The plane also measured peak SFMR winds of 41 kt to the north of the center.
Satellite images indicate that central convection is reforming…banding features are gradually increasing…and upper-level outflow is well-established in all quadrants except the northwest. Based upon the aircraft measurements and the increased organization on satellite images…Alex is once again upgraded to a tropical storm…and the advisory intensity is set at 40 kt.

Although the 12-hr average initial motion estimate is 300/6…shorter-term fixes suggest that Alex may be moving even slower. During the forecast period…global models forecast an unusually deep longwave trough to develop over the northeastern United States which should result in a temporary weakening of mid-level ridging along the northern Gulf Coast. The GFS/Canadian models continue to indicate a weaker version of the mid-level ridge and hence a more northwesterly or north-northwesterly motion…while the ECMWF/ UKMET/NOGAPS have consistently predicted a stronger ridge and move Alex on a more west-northwesterly course. The official new forecast
is quite similar to the previous advisory…and closely follows a consensus of the dynamical models that excludes the GFS…since the latter model appears to be somewhat of a northern outlier at this time.

Now that the center of Alex has emerged over the Gulf of Mexico…global models predict an environment characterized by light vertical wind shear as Alex moves over warm waters. Both of these ingredients should favor steady intensification until landfall. Perhaps the one negative factor is the large size of the circulation…as it may take some time for the cyclone to consolidate further. Given the favorable large-scale conditions… it is still puzzling that the GFDL/HWRF do not show Alex strengthening to more than a tropical storm during the next several days. Statistical guidance…on the other hand…continues to forecast a stronger tropical cyclone and the NHC intensity forecast
remains close to SHIPS/lgem model output. In any event…it should be noted that the skill of 2 to 3-day intensity forecasts is very low.

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