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| #873716 (Received by flhurricane at: 11:02 PM 01.Sep.2016) TCDAT4 HURRICANE HERMINE DISCUSSION NUMBER 19 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092016 1100 PM EDT THU SEP 01 2016 Reports from an Air Force Reserve Hurricane Hunter aircraft indicate that Hermine has gradually intensified since the last forecast advisory. The plane measured 86-kt flight-level winds southeast of the center at 850 mb with SFMR and dropsonde data suggesting winds of at least 65 kt. Based on these data and a earlier 983 mb central pressure, the initial intensity is set at 70 kt. The initial motion remains 030/12. The flow on the eastern side of a mid-level trough over the southeastern United States should cause Hermine to move north-northeastward to northeastward with an increase in forward speed during the next 36 hours. The track guidance is tightly clustered during this period, and this part of the forecast track is an update of the previous track. At 48 hours and beyond, Hermine is expected to interact with a baroclinic trough over the northeastern United States. The track guidance become rather divergent during this period, with the GFS and ECMWF models showing a looping track close to the coast, while the UKMET and Canadian models show a slow motion somewhat farther offshore. The new forecast track compromises between these solutions and shows a slow northeastward motion during this time. Regardless of the exact track, Hermine should linger for several days near the northeastern U. S. coast as a vigorous low pressure system. A little more strengthening is possible during the last few hours before landfall. After landfall, Hermine is expected to weaken as it crosses the southeastern United States, eventually emerging from the North Carolina coast as a tropical storm. The cyclone is expected to re-intensify as an extratropical low during its interaction with the baroclinic trough. The forecast intensities have been raised for this part of the forecast based on global model forecasts, and it is possible that they are a little conservative. Later in the forecast period, vertical shear decreases, and the cyclone could be situated over marginally warm waters. Therefore there is the possibility of the system regaining some tropical characteristics in 4-5 days, although this remains speculative. KEY MESSAGES: 1. As landfall occurs, it is important to not focus on the exact forecast track. Hermine is an extremely 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 become a post-tropical cyclone while still producing hazardous winds and storm surge over land. NWS policy allows NHC to write advisories on and issue tropical storm watches and warnings for post-tropical cyclones, when the system continues to pose a significant threat to life and property. NHC and the NWS Eastern Region have decided that this option will be invoked for Hermine. After Hermine becomes a post-tropical cyclone, NHC will continue to issue its full suite of advisory and warning products for as long as the system remains a significant threat to land. FORECAST POSITIONS AND MAX WINDS INIT 02/0300Z 29.7N 84.3W 70 KT 80 MPH 12H 02/1200Z 31.5N 82.8W 60 KT 70 MPH 24H 03/0000Z 33.6N 79.7W 45 KT 50 MPH...INLAND 36H 03/1200Z 35.6N 75.7W 45 KT 50 MPH...INLAND 48H 04/0000Z 37.0N 73.2W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 05/0000Z 38.0N 72.5W 55 KT 65 MPH...POST-TROP/EXTRATROP 96H 06/0000Z 39.0N 72.0W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 07/0000Z 39.5N 70.5W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Beven |
