ZCZC MIATCDAT3 ALL TTAA00 KNHC DDHHMM Hurricane Helene Discussion Number 21 NWS National Hurricane Center Miami FL AL082018 1100 AM AST Wed Sep 12 2018 The eye has become less distinct, but the overall convective pattern remains well organized and symmetric. Based on the latest Dvorak estimates, the initial intensity is kept at 80 kt. Most of the guidance show a significant increase in the shear in 24 hours, but the SSTs are not changing much for the next 2 days or so, thus gradual weakening is forecast. After that time, both shear and SSTs will become belligerently unfavorable, resulting in additional weakening. By the end of the forecast period, Helene should have acquired extratropical characteristic. The hurricane is moving toward the north-northwest or 340 degrees at 12 kt, embedded in the southerly flow to the east of the digging trough over the central Atlantic. Since the trough is forecast to amplify, Helene will be forced to turn to the north-northeast and northeast with an increase in forward speed. The global models remain in fairly good agreement on the current forecast track of Helene, and they all bring the cyclone near the Azores in 3 or 4 days. Interests in those islands should closely monitor the progress of Helene over the next several days. FORECAST POSITIONS AND MAX WINDS INIT 12/1500Z 20.3N 36.5W 80 KT 90 MPH 12H 13/0000Z 22.0N 37.2W 70 KT 80 MPH 24H 13/1200Z 24.5N 37.5W 65 KT 75 MPH 36H 14/0000Z 27.5N 37.2W 60 KT 70 MPH 48H 14/1200Z 31.0N 36.5W 50 KT 60 MPH 72H 15/1200Z 37.7N 33.2W 45 KT 50 MPH 96H 16/1200Z 42.5N 26.0W 45 KT 50 MPH 120H 17/1200Z 47.5N 17.5W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Avila NNNN
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