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Hurricane Irma Forecast Discussion Number 24
2017-09-05 10:49:05| National Hurricane Center (Atlantic)
Issued at 500 AM AST Tue Sep 05 2017 000 WTNT41 KNHC 050848 TCDAT1 Hurricane Irma Discussion Number 24 NWS National Hurricane Center Miami FL AL112017 500 AM AST Tue Sep 05 2017 The cloud pattern on satellite is spectacular with a clear eye surrounded by a ring of very deep convection. An Air Force plane was in the eye of the hurricane a few hours ago and measured surface winds of 126 kt with the SFMR. Since the plane left, the could pattern has become even more impressive and objective T-numbers have been oscillating around 7.0 on the Dvorak scale. Based on the average of these estimates, the initial intensity is adjusted upward to 130 kt. The hurricane will be moving through an environment of low vertical wind shear, a moist mid-level atmosphere, and increasing upper-ocean heat content, and this is ideal for some additional intensification. However, given that the SHIPS models do not show any significant change in the intensity, the NHC forecast keeps Irma a powerful hurricane through five days. Recon and satellite fixes indicate that Irma is moving toward the west or 270 degrees at 12 kt. The hurricane is moving around the periphery of the Atlantic subtropical ridge, which in fact is quite strong at this time. This persistent pattern should keep Irma on a general westward track for the next 24 hours, with a west-northwest track thereafter. The guidance envelope and many of the ensemble members of the GFS and the ECMWF models have shifted slightly westward since the previous run. The NHC forecast also shifted slightly westward, and it is on top of the multi-model consensus. The confidence in the forecast beyond 3 days is lower, since the guidance spreads out more. 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 expected to affect the northeastern Leeward Islands as a dangerous major hurricane, accompanied by life-threatening wind, storm surge, and rainfall impacts. Hurricane warnings are in effect for portions of the Leeward Islands. Preparations should be rushed to completion, as tropical-storm force winds are expected to first arrive in the hurricane warning area later today. 2. Irma is also expected to affect the British and U.S. Virgin Islands and Puerto Rico as a dangerous major hurricane later this week. Hurricane warnings have been issued for these areas, and tropical-storm-force winds could arrive in these areas by early Wednesday. 3. Irma could directly affect Hispaniola, the Turks and Caicos, the Bahamas, and Cuba as a dangerous major hurricane later this week. Residents in these areas should monitor the progress of Irma and listen to advice given by officials. 4. There is an increasing chance of seeing some impacts from Irma in the Florida Peninsula and the Florida Keys later this week and this weekend. Otherwise, it is still too early to determine what direct impacts Irma might have on the continental United States. However, everyone in hurricane-prone areas should ensure that they have their hurricane plan in place. FORECAST POSITIONS AND MAX WINDS INIT 05/0900Z 16.6N 57.0W 130 KT 150 MPH 12H 05/1800Z 17.0N 58.9W 130 KT 150 MPH 24H 06/0600Z 17.7N 61.5W 130 KT 150 MPH 36H 06/1800Z 18.6N 64.2W 130 KT 150 MPH 48H 07/0600Z 19.6N 67.0W 125 KT 145 MPH 72H 08/0600Z 21.2N 72.5W 120 KT 140 MPH 96H 09/0600Z 22.4N 77.2W 115 KT 130 MPH 120H 10/0600Z 24.0N 81.0W 115 KT 130 MPH $$ Forecaster Avila
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