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ZCZC MIATCDAT1 ALL TTAA00 KNHC DDHHMM Hurricane Irma Discussion Number 26 NWS National Hurricane Center Miami FL AL112017 1100 AM AST Tue Sep 05 2017 Irma is an extremely impressive hurricane in both infrared and visible satellite images. Experimental GOES-16 one-minute visible satellite pictures show a distinct 25-30 n mi wide eye with several mesovortices rotating within with eye. The aircraft have not sampled the northeastern eyewall where the strongest winds were measured shortly before 1200 UTC this morning, but the Air Force plane will be entering the eye in that quadrant momentarily. A peak SFMR wind of 154 kt was reported, with a few others of 149-150 kt. Based on these data the initial intensity is set at 155 kt for this advisory. This makes Irma the strongest hurricane in the Atlantic basin outside of the Caribbean Sea and Gulf of Mexico in the NHC records. Irma is expected to remain within low vertical wind shear, a moist mid-level atmosphere, and high upper-ocean heat content as it moves west-northwestward during the next several days. These conditions should allow the hurricane to remain very intense throughout much of the forecast period, however, fluctuations in intensity are likely to occur as eyewall replacement cycles take place. The NHC intensity forecast is near the upper-end of the guidance and assumes little overall interaction of Irma with the islands of the Greater Antilles. Irma continues to move westward at about 12 kt, and a strong subtropical ridge centered over the central Atlantic should steer Irma generally westward today. The ridge is expected to remain in place over the western Atlantic during the next several days and Irma is forecast to move west-northwestward throughout the most of remainder of the forecast period. Around day 5, a shortwave trough dropping southward over the central United States is expected to begin eroding the western portion of the ridge, allowing a Irma to gain some latitude. The new NHC track forecast is close to the HFIP corrected consensus model and is very similar to the previous forecast. Since Irma is a large hurricane, users are reminded to not focus on the exact forecast track since tropical-storm and hurricane-force winds and life-threatening storm surge extend far from the center. Residents in the Leeward Islands should complete their preparations very soon as the weather will begin to deteriorate over the easternmost Leeward Islands later this afternoon. KEY MESSAGES: 1. Irma is a potentially catastrophic category 5 hurricane and will bring life-threatening wind, storm surge, and rainfall hazards to portions of the northeastern Leeward Islands beginning later today and the Virgin Islands and Puerto Rico beginning tomorrow. Preparations should be rushed to completion before the arrival of tropical-storm force winds later today in the Leeward Islands and tomorrow morning in Virgin Islands and Puerto Rico. 2. Hurricane watches have been issued for portions of the Dominican Republic and Haiti, the southeastern Bahamas and Turks and Caicos, and Irma could bring dangerous wind, storm surge, and rainfall to those areas on Thursday and Friday. 3. Irma could directly affect the remainder of the Bahamas and Cuba as an extremely dangerous major hurricane later this week. Residents in these areas should monitor the progress of Irma and listen to advice given by officials. 4. The chance of direct impacts from Irma later this week and this weekend is increasing in the Florida Keys and portions of the Florida Peninsula. However, it is too soon to specify the timing and magnitude of the impacts. Elsewhere, it is too early to determine what direct impacts Irma might have on the continental United States. Everyone in hurricane-prone areas should ensure that they have their hurricane plan in place. FORECAST POSITIONS AND MAX WINDS INIT 05/1500Z 16.8N 58.4W 155 KT 180 MPH 12H 06/0000Z 17.2N 60.3W 155 KT 180 MPH 24H 06/1200Z 18.1N 63.0W 150 KT 175 MPH 36H 07/0000Z 19.1N 65.9W 145 KT 165 MPH 48H 07/1200Z 20.1N 68.7W 140 KT 160 MPH 72H 08/1200Z 21.4N 74.0W 135 KT 155 MPH 96H 09/1200Z 22.7N 78.3W 130 KT 150 MPH 120H 10/1200Z 24.4N 81.2W 125 KT 145 MPH $$ Forecaster Brown NNNN