ZCZC MIATCDAT1 ALL TTAA00 KNHC DDHHMM Hurricane Irma Discussion Number 41 NWS National Hurricane Center Miami FL AL112017 500 AM EDT Sat Sep 09 2017 The eye of Irma has been moving over the islands along the north coast of Cuba, and satellite imagery along with preliminary data from an Air Force Reserve Hurricane Hunter aircraft indicates that the hurricane has weakened. The initial intensity is reduced to 135 kt, and this may be generous. The initial motion is now 285/10. Irma is moving along the southwestern side of the subtropical ridge, which is about to weaken due to a mid- to upper-level trough moving into the southeastern United States. The track guidance is in good agreement that Irma should continue west-northwestward for the next 12-24 h, followed by a turn toward the north-northwest that would take the center parallel to the west coast of the Florida peninsula. Later in the forecast period, the cyclone should turn northwestward and eventually stall as it interacts with the aforementioned trough. The track guidance has changed only slightly since the previous advisory. Thus the new forecast track follows the previous forecast in calling for Irma to move along the coast of Cuba, then over the Lower Florida Keys, and then over and near the Florida West coast. It should be noted that because of the hurricane's angle of approach to the west coast of Florida, it is extremely difficult to pinpoint exactly where the center might move onshore. There is an opportunity for Irma to re-intensity as it crosses the warm waters of the Florida Straits. However, the large-scale models forecast significant westerly shear developing at about 24 h, and it is unclear how much strengthening could occur before then. The first part of the intensity forecast thus calls for little change in strength through 36 h, and Irma is still expected to be a dangerous hurricane as it approaches the Florida Keys and the west coast of Florida. After that time, movement over land and strong shear should cause steady weakening, with Irma eventually decaying to a remnant low by the end of the forecast period. KEY MESSAGES: 1. Irma will continue to bring life-threatening wind, storm surge, and rainfall hazards to portions of the Bahamas and the north coast of Cuba, especially over the adjacent Cuban Keys, through tonight. 2. Irma is expected to make landfall in Florida as an extremely dangerous major hurricane, and will bring life-threatening wind impacts to much of the state regardless of the exact track of the center. 3. There is the danger of life-threatening storm surge inundation in portions of central and southern Florida, including the Florida Keys, during the next 36 hours, where a Storm Surge Warning is in effect. The threat of significant storm surge flooding along the southwest coast of Florida has increased, and 8 to 12 feet of inundation above ground level is possible in this area. This is a life-threatening situation. Everyone in these areas should take all actions to protect life and property from rising water and follow evacuation instructions from local officials. 4. Irma is expected to produce very heavy rain and inland flooding. Total rain accumulations of 8 to 15 inches, with isolated amounts of 20 inches are expected over the Florida Keys and much of the Florida peninsula through Tuesday night. Irma will likely bring periods of heavy rain to much of the Florida Panhandle, Georgia, South Carolina, and western North Carolina early next week, including some mountainous areas which are more prone to flash flooding. All areas seeing heavy rainfall from Irma will experience a risk of flooding and flash flooding. FORECAST POSITIONS AND MAX WINDS INIT 09/0900Z 22.5N 78.8W 135 KT 155 MPH 12H 09/1800Z 22.9N 80.0W 130 KT 150 MPH 24H 10/0600Z 23.8N 81.1W 130 KT 150 MPH 36H 10/1800Z 25.4N 81.8W 130 KT 150 MPH 48H 11/0600Z 27.7N 82.4W 105 KT 120 MPH...INLAND 72H 12/0600Z 32.5N 84.5W 45 KT 50 MPH...INLAND 96H 13/0600Z 35.5N 88.0W 25 KT 30 MPH...INLAND 120H 14/0600Z 36.0N 87.5W 20 KT 25 MPH...POST-TROP/INLAND $$ Forecaster Beven NNNN
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