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Hurricane Irma Forecast Discussion Number 32
2017-09-07 04:57:16| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Wed Sep 06 2017 000 WTNT41 KNHC 070257 TCDAT1 Hurricane Irma Discussion Number 32 NWS National Hurricane Center Miami FL AL112017 1100 PM AST Wed Sep 06 2017 Earlier radar observations from the San Juan WSR-88D showed a concentric eyewall, and observations from an Air Force Hurricane Hunter aircraft showed a secondary wind maximum over the northwest quadrant. These phenomena may be associated with some weakening, but since the central pressure hasn't risen much the intensity is held at 160 kt at this time. Moreover, the concentric eyewall has become less apparent in recent radar imagery. Considerable lightning activity has been noted in the eyewall of Irma, which research has shown to sometimes be a harbinger of weakening. Notwithstanding, low vertical wind shear and warm waters along the forecast track of Irma should allow it to remain a very powerful hurricane during the next several days. The official intensity forecast is similar to the previous one except at day 5 when stronger shear should cause more weakening. This forecast is generally above the intensity model consensus. Irma continues on a west-northwestward heading at around 14 kt. A ridge of high pressure over the western Atlantic should maintain this course for the next 48 to 72 hours. Later in the forecast period a shortwave trough moving into the southeastern United States is likely to turn the hurricane northwestward to north-northwestward. There has been a slight eastward shift in some of the track guidance models, but since the models could shift back to the west it is prudent to make little change to the official forecast at this time. In any event, users are reminded not to focus on the exact track since the average NHC track errors at days 4 and 5 are about 175 and 225 miles, respectively. KEY MESSAGES: 1. Irma is a potentially catastrophic category 5 hurricane and will bring life-threatening wind, storm surge, and rainfall hazards to Puerto Rico tonight, the northern coast of Hispaniola Thursday, and the Turks and Caicos and southeastern and central Bahamas Thursday and Friday. 2. Hurricane watches are in effect for the northwestern Bahamas and much of Cuba. Irma is likely to bring dangerous wind, storm surge, and rainfall to portions of these areas on Friday and Saturday. 3. The threat of direct hurricane impacts in Florida over the weekend and early next week has increased. Hurricane watches will likely be issued for portions of the Florida Keys and the Florida peninsula on Thursday. FORECAST POSITIONS AND MAX WINDS INIT 07/0300Z 19.4N 66.8W 160 KT 185 MPH 12H 07/1200Z 20.3N 68.8W 155 KT 180 MPH 24H 08/0000Z 21.3N 71.7W 150 KT 175 MPH 36H 08/1200Z 22.1N 74.1W 145 KT 165 MPH 48H 09/0000Z 22.7N 76.3W 140 KT 160 MPH 72H 10/0000Z 24.0N 79.3W 135 KT 155 MPH 96H 11/0000Z 27.4N 80.3W 120 KT 140 MPH 120H 12/0000Z 32.0N 81.0W 95 KT 110 MPH $$ Forecaster Pasch
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