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Hurricane Irma Forecast Discussion Number 28
2017-09-06 04:36:40| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Tue Sep 05 2017 000 WTNT41 KNHC 060236 TCDAT1 Hurricane Irma Discussion Number 28 NWS National Hurricane Center Miami FL AL112017 1100 PM AST Tue Sep 05 2017 The satellite view of Irma remains quite spectacular, with an extremely well-defined eye and a large, symmetrical CDO. Reports from NOAA and Air Force Hurricane Hunter aircraft indicate that the central pressure had fallen at about 1 mb per hour since this morning, although very recently the deepening trend has leveled off. Based on SFMR-observed winds from the aircraft, the current intensity remains at 160 kt. The Meteo-France radar imagery suggests a concentric eyewall structure and observations from the aircraft hinted at a secondary wind maximum. If an eyewall replacement becomes more definitive, this would likely halt additional strengthening, and could even lead to some weakening. The official intensity forecast is near or above the model consensus. Given the favorable atmospheric and oceanic environment, Irma is likely to remain a Category 4 or 5 hurricane for the next few days. Latest center fixes from satellite imagery and the aircraft indicate that Irma is now moving west-northwestward, or 285/13 kt. A strong ridge extending southwestward from the central Atlantic is expected to steer Irma west-northwestward during the next 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. In 4 to 5 days, a small trough diving southward over the east-central U.S. is expected to weaken the western portion of the ridge, causing Irma to turn poleward. Some of the dynamical models have shifted northward a bit from the previous cycle, with the normally reliable GFS looking like a northeast outlier. The official track forecast leans toward the ECMWF solution. 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 northern Leeward Islands, including the Virgin Islands and Puerto Rico, on Wednesday. Preparations should be rushed to completion. 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 06/0300Z 17.4N 61.1W 160 KT 185 MPH 12H 06/1200Z 18.1N 63.1W 155 KT 180 MPH 24H 07/0000Z 19.1N 65.9W 150 KT 175 MPH 36H 07/1200Z 20.1N 68.5W 145 KT 165 MPH 48H 08/0000Z 21.0N 71.2W 140 KT 160 MPH 72H 09/0000Z 22.0N 76.2W 135 KT 155 MPH 96H 10/0000Z 23.2N 79.5W 125 KT 145 MPH 120H 11/0000Z 25.0N 81.5W 120 KT 140 MPH $$ Forecaster Pasch
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