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Hurricane Irma Forecast Discussion Number 30
2017-09-06 16:48:09| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Wed Sep 06 2017 000 WTNT41 KNHC 061448 TCDAT1 Hurricane Irma Discussion Number 30 NWS National Hurricane Center Miami FL AL112017 1100 AM AST Wed Sep 06 2017 The eye of Irma passed over Barbuda, St. Barthelemy, and St. Martin this morning, and will be moving over portions of the British and U.S. Virgin Islands shortly. A NOAA National Ocean Service observing site on Barbuda measured sustained winds of 103 kt with a gust to 135 kt earlier this morning before the anemometer failed. The station also reported a minimum pressure of 916.1 mb. A minimum pressure of 915.9 mb was reported on St. Barthelemy. An Air Force reconnaissance aircraft that performed a single pass through the eye this morning reported SFMR winds of 152 kt in the northwestern eyewall around 12Z. Assuming there are stronger winds in the northeastern eyewall, the initial intensity remains 160 kt for this advisory. Another Air Force aircraft is currently entering the storm. Irma is moving west-northwestward or 285/14 kt. A strong high pressure ridge extending from the central Atlantic westward is expected to keep Irma moving west-northwestward during the next 2 to 3 days. The track guidance is in good agreement during this period and the NHC track is along the southern edge of the guidance envelope in best agreement with the ECMWF and HFIP corrected consensus model. After that time, a shortwave trough moving southward over the east-central United States is expected to erode the western portion of the ridge. As a result, Irma is forecast to turn northwestward and northward, but there is still a fair amount of uncertainty regarding the exact timing and location of recurvature. The NHC forecast has been shifted eastward to be in better agreement with the latest model guidance, however it should be noted that there are numerous GEFS and ECMWF ensemble members that take Irma over and/or west of Florida. The updated NHC track is in best agreement with the latest ECMWF ensemble mean. Users are reminded that the average NHC track errors at days 4 and 5 are about 175 and 225 statue miles, respectively. Irma is forecast to remain within favorable atmospheric conditions and over warm waters during the next 3 to 4 days. Therefore, Irma is likely to remain a very powerful hurricane during this time, and the NHC intensity forecast is unchanged from the previous advisory through day 4. Since the 120-h forecast point is now offshore, the intensity forecast at that time has been adjusted accordingly. Now that Irma's eye is clearly visible in radar imagery from San Juan, Tropical Cyclone Updates with hourly position estimates will be issued starting at 1200 PM AST (1600 UTC). 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 today. 2. A hurricane warning is in effect for the northern coast of the Dominican Republic, the southeastern Bahamas, the Turks and Caicos, and portions of Haiti, with a hurricane watch in effect for the central Bahamas and much of Cuba. Irma is likely to bring dangerous wind, storm surge, and rainfall to some of these areas tonight 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. Direct impacts from wind, storm surge, and rainfall are possible in the Florida Keys and portions of the Florida Peninsula beginning later this week and this weekend. However, given the forecast uncertainty at these time ranges, it is too soon to specify the location and magnitude of these impacts. FORECAST POSITIONS AND MAX WINDS INIT 06/1500Z 18.2N 64.0W 160 KT 185 MPH 12H 07/0000Z 19.0N 66.2W 155 KT 180 MPH 24H 07/1200Z 20.2N 69.0W 150 KT 175 MPH 36H 08/0000Z 21.2N 71.7W 145 KT 165 MPH 48H 08/1200Z 21.9N 74.2W 140 KT 160 MPH 72H 09/1200Z 22.9N 78.1W 135 KT 155 MPH 96H 10/1200Z 25.2N 80.0W 125 KT 145 MPH 120H 11/1200Z 29.0N 80.5W 110 KT 125 MPH $$ Forecaster Brown
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