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ZCZC MIATCDAT1 ALL TTAA00 KNHC DDHHMM Hurricane Irma Discussion Number 14 NWS National Hurricane Center Miami FL AL112017 500 PM AST Sat Sep 02 2017 Hurricane Irma continues to display an eye within a small central dense overcast, although the eye has been going through periods where it becomes less well defined. The satellite intensity estimates from TAFB and SAB remain 90 kt, while the latest CIMMS ADT and satellite consensus technique estimates ARE 95-105 KT. Since there has been little overall change in organization since the last advisory, the initial intensity remains 95 kt. The environment in which Irma is embedded continues to show mixed signals during the forecast period, and the intensity guidance responds to this by ranging between little and slow intensification. The hurricane is currently suffering some impact of sea surface temperatures of about 27C and mid-level dry air entrainment. Later in the period, Irma should encounter warmer water and increasing moisture at a time when the vertical wind shear may be increasing. Given the uncertainty on when all of the ingredients may come together, the new intensity forecast is the same as the previous forecast and calls for gradual intensification through the next 5 days. An alternative forecast scenario is that Irma gets significantly stronger than forecast near the end of the forecast period if the shear is less than currently expected. The initial motion remains 265/13. A large and building subtropical ridge should steer Irma generally west-southwestward during the next two days or so. Between 72-120 h, Irma should be rounding the southwestern periphery of the ridge and start turning back toward the west-northwest. While the track guidance remains in good agreement with this scenario, from 72-120 h there has been a westward shift of the guidance that results in the new forecast track coming 30-60 n mi closer to the Leeward and Virgin Islands than in the previous advisory. This latter portion of the track lies near the center of the guidance envelope, but with the ECMWF and corrected consensus models to the south and the GFS to the north. 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 02/2100Z 18.5N 44.6W 95 KT 110 MPH 12H 03/0600Z 18.0N 46.5W 95 KT 110 MPH 24H 03/1800Z 17.4N 48.8W 100 KT 115 MPH 36H 04/0600Z 17.0N 50.9W 105 KT 120 MPH 48H 04/1800Z 16.8N 53.0W 110 KT 125 MPH 72H 05/1800Z 17.5N 57.5W 110 KT 125 MPH 96H 06/1800Z 19.5N 62.5W 115 KT 130 MPH 120H 07/1800Z 22.0N 68.0W 115 KT 130 MPH $$ Forecaster Beven NNNN