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Tropical Storm Irma Forecast Discussion Number 50
2017-09-11 16:52:48| National Hurricane Center (Atlantic)
Issued at 1100 AM EDT Mon Sep 11 2017 000 WTNT41 KNHC 111452 TCDAT1 Tropical Storm Irma Discussion Number 50 NWS National Hurricane Center Miami FL AL112017 1100 AM EDT Mon Sep 11 2017 Irma continues to weaken while moving over extreme northern Florida with most of the deep convection displaced well to the north and northeast of the center due to strong shear. In fact, global model analyses suggest that the system has partial extratropical characteristics, with some associated cold and warm air advection. The current intensity is set at 55 kt which is in line with the highest sustained winds seen in surface observations. Since the cyclone is very large its weakening will be fairly gradual, but the effects of land and shear should reduce the system to a depression in about 24 hours. Shortly thereafter Irma will likely become a remnant low, with complete dissipation by 72 hours as shown by the dynamical guidance. The initial motion continues to be north-northwestward or 340/15 kt. Not much change has been made to the NHC track forecast. Irma or its remnant should continue to move along the eastern and northeastern periphery of a broad mid-level cyclonic circulation until dissipation. The official track forecast is close to the latest corrected multi-model consensus. KEY MESSAGES: 1. There is the danger of life-threatening storm surge flooding along portions of the coasts of Florida, Georgia and South Carolina, where a Storm Surge Warning remains in effect. 2. Irma continues to produce very heavy rain and inland flooding across much of the northern peninsula and eastern panhandle of Florida, and southern Georgia, which is quickly spreading to the rest of the southeast United States. Intense rainfall rates of 2 inches or more per hour is leading to flash flooding and rapid rises on creeks, streams, and rivers. Significant river flooding is likely over the next five days in the Florida peninsula and southern Georgia, where average rainfall totals of 8 to 15 inches are expected. Significant river flooding is possible beginning Monday and Tuesday in much of central Georgia and southern South Carolina where average rainfall of 3 to 6 inches and isolated 10 inch amounts are expected. Portions of these states within the southern Appalachians will be especially vulnerable to flash flooding. FORECAST POSITIONS AND MAX WINDS INIT 11/1500Z 30.3N 83.1W 55 KT 65 MPH...INLAND 12H 12/0000Z 32.0N 84.5W 50 KT 60 MPH...INLAND 24H 12/1200Z 33.9N 86.6W 30 KT 35 MPH...INLAND 36H 13/0000Z 35.0N 88.4W 25 KT 30 MPH...POST-TROP/INLAND 48H 13/1200Z 36.0N 89.0W 20 KT 25 MPH...POST-TROP/INLAND 72H 14/1200Z...DISSIPATED $$ Forecaster Pasch
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