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| #873805 (Received by flhurricane at: 10:59 AM 02.Sep.2016) TCDAT4 TROPICAL STORM HERMINE DISCUSSION NUMBER 21 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092016 1100 AM EDT FRI SEP 02 2016 Hermine is moving over southeastern Georgia and has weakened steadily since landfall. Convective tops have warmed, but several land stations have shown sustained winds near tropical storm force near the center with some gusts close to 50 kt. Stronger winds are also found over the Atlantic coastal waters, with buoy 41008 reporting winds around 40 kt in the last hour. Based on this, the initial intensity is set to 45 kt for this advisory. The central pressure, based on surface data, is about 989 mb. While the center of Hermine will remain over land for the next 24 hours or so, I don't expect the winds over water to decrease much, so the NHC forecast shows no change during that time. Strengthening through a combination of diabatic and baroclinic processes is shown after the system moves offshore. The GFS, ECMWF, and UKMET all show Hermine interacting with a potent upper-level shortwave trough in 2-3 days, and the system could re-strengthen to near hurricane force at that time. Slow weakening is expected later in the period, but Hermine is expected to remain a dangerous cyclone through 5 days. The NHC intensity forecast is based largely on global model guidance, and is a bit higher than the previous one. The initial motion estimate is 040/16. Hermine should continue moving northeastward for the next 36 to 48 hours ahead of an approaching mid-latitude trough. After that time, the cyclone should turn northward and nearly stall out as it interacts with the upper-level shortwave off the mid-Atlantic coast. A slow northeastward motion is shown at days 4 and 5, but there is a fair bit of model spread late in the period and confidence in the details of the track forecast at those times remains low. Note that the NHC forecast shows Hermine as a post-tropical cyclone in about 48 hours, but model fields do not show it undergoing a full extratropical transition, as it instead appears to acquire a warm seclusion structure. There is a possibility that the system could regain some tropical characteristics in 4-5 days, but this remains uncertain. Based on the latest forecast, tropical storm watches and warnings have been expanded northward along the U.S. mid-Atlantic coast. KEY MESSAGE: 1. 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 02/1500Z 31.9N 82.0W 45 KT 50 MPH...INLAND 12H 03/0000Z 33.5N 79.7W 45 KT 50 MPH...INLAND 24H 03/1200Z 35.4N 76.3W 45 KT 50 MPH...INLAND 36H 04/0000Z 36.7N 73.9W 55 KT 65 MPH...OVER WATER 48H 04/1200Z 37.5N 72.6W 55 KT 65 MPH...POST-TROPICAL 72H 05/1200Z 38.1N 72.6W 65 KT 75 MPH...POST-TROPICAL 96H 06/1200Z 38.8N 71.9W 60 KT 70 MPH...POST-TROPICAL 120H 07/1200Z 39.3N 71.5W 50 KT 60 MPH...POST-TROPICAL $$ Forecaster Brennan |
