Sebastien Expected To Become A Hurricane By Tonight

From the National Hurricane Center:

SUMMARY OF 900 AM CST…1500 UTC…INFORMATION
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LOCATION…23.5N 60.5W
ABOUT 405 MI…650 KM NNE OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS…60 MPH…95 KM/H
PRESENT MOVEMENT…NNE OR 30 DEGREES AT 8 MPH…13 KM/H
MINIMUM CENTRAL PRESSURE…999 MB…29.50 INCHES

Sebastien continues to produce a large area of deep convection over the eastern semicircle of the circulation, but the banding features are not very well defined. The intensity estimate remains at 50 kt based on a blend of subjective Dvorak estimates from TAFB and SAB. A diffluent upper-level wind environment and warm waters are expected to bring about some strengthening through tonight, however the window of opportunity for strengthening will probably close tomorrow morning. After that time, drier air and strong shear should cause gradual weakening. The official intensity forecast is a little above the model consensus. In a couple of days, the GFS shows Sebastien becoming embedded in a frontal zone, signifying the transition to an extratropical cyclone as shown in the NHC forecast. The ECMWF model suggests that this event could occur later, but the current close proximity of a front to Sebastian argues for extratropical transition to occur within 48 hours.

The circulation is a bit elongated from south to north, and the center remains difficult to locate. This results in a greater than normal uncertainty in the initial motion, and my best guess is 030/7 kt. A turn toward the northeast, with acceleration, is expected during the next couple of days due to the influence of a mid-level trough. There is considerable along-track model spread, with the ECMWF forecast being much slower than the majority of the guidance. The official forecast is somewhat slower than the dynamical model consensus out of respect for that typically reliable model.

Category: ALL POSTS, Tropical