ZCZC MIATCDAT1 ALL TTAA00 KNHC DDHHMM Tropical Storm Irma Discussion Number 51 NWS National Hurricane Center Miami FL AL112017 500 PM EDT Mon Sep 11 2017 Surface synoptic data over the southeastern United States indicate that Irma continues to weaken. The maximum winds are now near 45 kt, and these are confined to the Georgia and South Carolina coastal area, along with some winds to tropical storm force in interior central to northern Georgia. Irma continues to have some extratropical characteristics, since a fairly well-defined baroclinic zone lies not far from the center. Nevertheless, the large circulation should continue to spin down due to land interaction and strong southwesterly shear. The official intensity forecast is above most of the guidance, so the system could weaken faster than shown here. Irma should weaken to a depression in 24 hours or sooner, and the global guidance shows the circulation dissipating over the east-central United States after 48 hours. Synoptic center fixes give a continued north-northwestward motion of 340/15 kt. There is little change to the track forecast reasoning. For the next day or two, Irma or its remnants should move on a north-northwestward to northwestward track along the periphery of a broad mid-level cyclonic gyre. The official forecast is a blend of the latest GFS and ECMWF solutions. KEY MESSAGES: 1. There is the danger of life-threatening storm surge flooding along portions of the coasts of western Florida, Georgia, and South Carolina, where Storm Surge Warnings remain in effect. 2. Irma is producing very heavy rain across the southeastern United States. Intense rainfall rates are leading to flash flooding and rapid rises on creeks, streams, and rivers. Significant river flooding will persist over the Florida peninsula in the wake of Irma and in Georgia, South Carolina and north-central Alabama, where additional heavy rains are expected. Portions of these states within the southern Appalachians will be especially vulnerable to flash flooding. Irma is also expected to produce heavy rains in northern Mississippi and southern portions of Tennessee and North Carolina, where local flooding may occur. FORECAST POSITIONS AND MAX WINDS INIT 11/2100Z 31.5N 84.0W 45 KT 50 MPH...INLAND 12H 12/0600Z 33.1N 85.5W 35 KT 40 MPH...INLAND 24H 12/1800Z 34.5N 87.3W 30 KT 35 MPH...INLAND 36H 13/0600Z 35.8N 88.8W 25 KT 30 MPH...POST-TROP/INLAND 48H 13/1800Z 37.0N 88.5W 20 KT 25 MPH...POST-TROP/INLAND 72H 14/1800Z...DISSIPATED $$ Forecaster Pasch NNNN
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