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Tropical Storm HERMINE Forecast Discussion Number 16
2016-09-01 17:00:25| National Hurricane Center (Atlantic)
Issued at 1000 AM CDT THU SEP 01 2016 000 WTNT44 KNHC 011500 TCDAT4 TROPICAL STORM HERMINE DISCUSSION NUMBER 16 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092016 1000 AM CDT THU SEP 01 2016 Hermine is gradually becoming better organized, with convective banding developing over the eastern semicircle of the circulation. Upper-level outflow continues to be restricted to the northwest of the storm by a cyclonic shear axis depicted by water vapor imagery. The current intensity is set at 55 kt in agreement with SFMR-observed surface winds from an Air Force Hurricane Hunter aircraft. The intensity forecast continues to show Hermine becoming a hurricane before landfall which is in general agreement with the numerical guidance. The global models show Hermine embedded within a frontal zone by 48 hours, so the forecast shows the system becoming extratropical at that time. There is some concern about the evolution of the post-tropical cyclone later in the forecast period, since the shear starts decreasing after 72 hours. This could allow the system to reacquire some tropical characteristics in 4-5 days, although it is not certain how close to the coast the cyclone will be by that time. Based on Hurricane Hunter aircraft fixes and a dropsonde from the NASA Global Hawk aircraft, the initial motion is estimated to be 030/12 kt. A mid-tropospheric trough should steer the system north-northeastward to northeastward for the next couple of days. Later in the forecast period, a developing mid-level cutoff low near the northeast United States coast will cause a slowing of the forward speed as the cyclone interacts with the low. The official forecast track is essentially a blend of the latest GFS and ECMWF solutions, with the former model showing a track closer to the northeast coast and the latter taking the system farther offshore. KEY MESSAGES: 1. It is important to not focus on the exact forecast track. Hermine is a rather asymmetric storm, with a large extent of dangerous winds, life-threatening storm surge, and flooding rains well to the east and southeast of the path of the center. 2. Hermine is expected to undergo a complex interaction with a frontal system when it reaches the Carolinas over the weekend. It is a little early to say what the specific impacts will be for the mid-Atlantic and northeastern states. FORECAST POSITIONS AND MAX WINDS INIT 01/1500Z 27.4N 86.0W 55 KT 65 MPH 12H 02/0000Z 29.0N 84.8W 65 KT 75 MPH 24H 02/1200Z 31.1N 82.9W 50 KT 60 MPH...INLAND 36H 03/0000Z 33.1N 80.0W 45 KT 50 MPH...INLAND 48H 03/1200Z 35.2N 76.7W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 04/1200Z 38.0N 72.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 05/1200Z 38.5N 71.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 06/1200Z 39.5N 70.5W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch
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