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| #901566 (Received by flhurricane at: 4:56 PM 05.Sep.2017) TCDAT1 Hurricane Irma Discussion Number 27 NWS National Hurricane Center Miami FL AL112017 500 PM AST Tue Sep 05 2017 Irma continues to exhibit a remarkably impressive satellite presentation. The intensity was increased to 160 kt on the 1800 UTC intermediate public advisory based on a couple of SFMR winds of 160 kt measured in the northeastern eyewall by the Air Force aircraft just prior to that time. The minimum pressure measured by a dropsonde in the eye was 926 mb. Irma becomes only the fifth Atlantic basin hurricane with a peak wind speed of 160 kt or higher. The others are Allen (1980), the Labor Day Hurricane of 1935, Gilbert (1988), and Wilma (2005). The eye of Irma is within range of the Meteo France radar in the northeastern Caribbean, and recent images show the development of an outer eyewall, likely the beginning stages of an eyewall replacement. These changes in inner-core structure will likely result in fluctuations in intensity during the next couple of days. Otherwise, increasing upper-ocean heat content and a very favorable upper-level pattern are expected to allow Irma to remain a category 4 or 5 hurricane during the next several days. Once again, the NHC forecast shows limited interaction of the hurricane with the islands of the Greater Antilles. Fixes from the latest satellite and radar imagery suggest that Irma is moving a little north of due west or 280/13 kt. A strong ridge extending southwestward from the central Atlantic is expected to steer Irma west-northwestward during the couple of days. A large mid-latitude trough over the eastern United States is forecast to lift northeastward, allowing the ridge to build westward and keep Irma on a westward to west-northwestward heading through Friday. Over the weekend, a shortwave trough diving southward over the east-central U.S. is expected to weaken the western portion of the ridge, causing Irma to turn poleward. The dynamical model guidance is in good agreement through 72 hours, but there is increasing spread thereafter. The HWRF, UKMET, and ECMWF show a more southerly track and a sharper turn around day 5, while the GFS is farther north and east late in the period. The NHC track is near a consensus of these models and close to the HFIP corrected consensus. Users are reminded to not focus on the exact forecast track, especially at the longer ranges, since the average NHC track errors are about 175 and 225 statute miles at days 4 and 5, respectively. 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 tonight and tomorrow. These hazards will spread into the Virgin Islands and Puerto Rico tomorrow. Preparations should be rushed to completion before the arrival of tropical-storm force winds tomorrow morning in Virgin Islands and Puerto Rico. 2. A hurricane warning is in effect for the northern coast of the Dominican Republic, with hurricane watches for Haiti, the southeastern Bahamas and the Turks and Caicos. Irma is likely to bring dangerous wind, storm surge, and rainfall to these areas from Wednesday night through 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 beginning later this week and this weekend from wind, storm surge, and rainfall continues to increase in the Florida Keys and portions of the Florida Peninsula. However, it is too soon to specify the timing and magnitude of these impacts. FORECAST POSITIONS AND MAX WINDS INIT 05/2100Z 17.1N 59.8W 160 KT 185 MPH 12H 06/0600Z 17.6N 61.8W 155 KT 180 MPH 24H 06/1800Z 18.5N 64.6W 150 KT 175 MPH 36H 07/0600Z 19.5N 67.3W 145 KT 165 MPH 48H 07/1800Z 20.4N 70.1W 140 KT 160 MPH 72H 08/1800Z 21.6N 75.3W 135 KT 155 MPH 96H 09/1800Z 22.7N 79.3W 125 KT 145 MPH 120H 10/1800Z 24.4N 81.5W 120 KT 140 MPH $$ Forecaster Brown |
