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Hurricane Irma Forecast Discussion Number 15
2017-09-03 04:32:14| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Sat Sep 02 2017 000 WTNT41 KNHC 030232 TCDAT1 Hurricane Irma Discussion Number 15 NWS National Hurricane Center Miami FL AL112017 1100 PM AST Sat Sep 02 2017 The cloud pattern of Irma has not changed significantly in structure today. The eye continues to become apparent and then hide under the convective canopy, and this has been the observed pattern for the past 24 hours or so. Dvorak estimates go up and down with the presence of the eye, but an average of these numbers supports an initial intensity of 95 kt. A NOAA Hurricane Hunter plane will help with the intensity estimate on Sunday. I hesitate to speculate too much about the environment that Irma is embedded within. All of the standard ingredients necessary for strengthening are forecast to be at least marginally favorable, but none are expected to be hostile for intensification. The NHC forecast, which in fact is similar to the previous one, continues to be a blend of the statistical models and the explosive strengthening shown by the regional hurricane and global models. The subtropical ridge building to the north of Irma has been steering the hurricane toward the west or 260 degrees at 12 kt. The ridge is forecast to amplify even more, and this flow pattern will force the hurricane to dive west-southwestward for a couple of days. Irma should then begin to gain latitude once it reaches the southwestern edge of the ridge in about 3 days. The confidence in the track forecast is high for the next 72 hours since all of the reliable guidance is basically on top of each other. After 3 days, when the hurricane is forecast to be approaching the northern Leeward Islands, the guidance envelope spreads out and becomes bounded by the southernmost tracks of the HWRF, HCCA and the ECMWF models, and by the northernmost GFS and UK models. The confidence beyond 3 days is then much lower. Tonight's NHC forecast was adjusted a just little to the south of the previous one due to another small shift of the guidance envelope. The forecast is basically on top of the multi-model consensus TVCX. While Irma is currently a small hurricane, the size guidance suggests it should grow in size during the next 72 h. This will affect how soon watches may be issued for portions of the Leeward and Virgin Islands. KEY MESSAGES: 1. Irma is expected to be a major hurricane when it moves closer to the Lesser Antilles early next week, producing rough surf and rip currents. Irma could also cause dangerous wind, storm surge, and rainfall impacts on some islands, although it is too soon to specify where and when those hazards could occur. Residents in the Lesser Antilles should monitor the progress of Irma through the weekend and listen to any advice given by local officials. 2. It is much too early to determine what direct impacts Irma will have on the Bahamas and the continental United States. Regardless, everyone in hurricane-prone areas should ensure that they have their hurricane plan in place, as we are now near the peak of the season. FORECAST POSITIONS AND MAX WINDS INIT 03/0300Z 18.3N 46.2W 95 KT 110 MPH 12H 03/1200Z 17.8N 48.0W 95 KT 110 MPH 24H 04/0000Z 17.2N 50.1W 100 KT 115 MPH 36H 04/1200Z 16.7N 52.3W 105 KT 120 MPH 48H 05/0000Z 16.5N 54.5W 110 KT 125 MPH 72H 06/0000Z 17.7N 59.3W 110 KT 125 MPH 96H 07/0000Z 19.9N 64.5W 115 KT 130 MPH 120H 08/0000Z 22.5N 69.5W 115 KT 130 MPH $$ Forecaster Avila
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