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Hurricane Irma Forecast Discussion Number 29
2017-09-06 10:54:38| National Hurricane Center (Atlantic)
Issued at 500 AM AST Wed Sep 06 2017 000 WTNT41 KNHC 060854 TCDAT1 Hurricane Irma Discussion Number 29 NWS National Hurricane Center Miami FL AL112017 500 AM AST Wed Sep 06 2017 Irma continues as a Category 5 hurricane this morning, having passed over Barbuda a few hours ago. Earlier data from an Air Force Reserve Hurricane Hunter aircraft included SFMR winds near 155 kt and that the central pressure had fallen to 914 mb inside the 25 n mi wide eye. There has been little change in the satellite appearance of the hurricane since that time, so the initial intensity remains 160 kt. The initial motion is 285/14. Irma is currently being steered by the subtropical ridge to the north, and a general west- northwestward motion on the south side of the ridge is expected during the next 48-72 h. This portion of the forecast track is little changed and is in best overall agreement with the ECMWF model. The forecast has become more uncertain after 72 h due to large eastward shifts by the ECMWF, Canadian, and HWRF models related to forecasts of the mid- to upper-level trough over the southeastern United States. The bulk of the guidance now calls for Irma to turn northward between 78W-80W, moving near or over the Florida east coast or the northwestern Bahamas. The official forecast has also been shifted eastward, but out of respect for the previous forecast and the possibility the guidance may shift back to the west, it lies to the left of the bulk of the guidance. The forecast now calls for landfall in south Florida between 96-120 h. 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. Irma is likely to remain in a light shear, warm water, environment for the next 3 to 4 days. The intensity guidance continues to show slow weakening during this time, and this part of the intensity forecast is little changed from the previous advisory, with Irma remaining a strong hurricane during this time. The intensity forecast is lowered at 120 h due to the forecast landfall, and even if Irma stays over water it is likely to encounter some vertical shear at that time. 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. Preparations should be rushed to completion. 2. A Hurricane Warning is in effect for the northern coast of the Dominican Republic, as well as the southeastern Bahamas and the Turks and Caicos, with hurricane watches for portions of Haiti and the central Bahamas. 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 06/0900Z 17.9N 62.6W 160 KT 185 MPH 12H 06/1800Z 18.6N 64.6W 155 KT 180 MPH 24H 07/0600Z 19.6N 67.3W 150 KT 175 MPH 36H 07/1800Z 20.6N 70.0W 145 KT 165 MPH 48H 08/0600Z 21.3N 72.5W 140 KT 160 MPH 72H 09/0600Z 22.5N 77.0W 135 KT 155 MPH 96H 10/0600Z 24.0N 80.0W 125 KT 145 MPH 120H 11/0600Z 26.5N 80.9W 105 KT 120 MPH...INLAND $$ Forecaster Beven
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