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Tropical Storm HERMINE Forecast Discussion Number 13
2016-08-31 22:52:59| National Hurricane Center (Atlantic)
Issued at 400 PM CDT WED AUG 31 2016 000 WTNT44 KNHC 312052 TCDAT4 TROPICAL STORM HERMINE DISCUSSION NUMBER 13 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092016 400 PM CDT WED AUG 31 2016 The system appears better organized on satellite images than it was yesterday, with more evidence of convective banding features. However, based on the NOAA Hurricane Hunter data the center is still situated near the northern edge of the main convective cloud mass. Also, data from the aircraft show a very asymmetric wind field with all of the strong winds occurring over the eastern and southeastern portions of the circulation. The advisory intensity is set to 40 kt based on SFMR-observed surface winds from the Hurricane Hunters. Hermine should be in an environment of moderate west-southwesterly shear until it nears the coast, when the dynamical models show increasing shear. The official intensity forecast has been nudged upward a bit, and there is a distinct possibility that Hermine could become a hurricane before landfall. The predicted extratropical transition of the system is based on the latest global model forecasts, which show the cyclone becoming embedded within a front over the eastern United States by 72 hours. The aircraft data show a rather broad area of light winds near the center, making the actual center fixes a little uncertain. However, the best estimate of initial motion is north-northeastward or 030/6 kt. A developing mid-level trough over the southeastern United States should cause Hermine to move north-northeastward at increasing forward speed over the next couple of days. The GFS and ECMWF global models have shifted westward from their previous predictions, and so has the new official forecast. This required a westward extension of the hurricane watch and tropical storm warning along the Florida panhandle. Later in the forecast period, there is significant uncertainty in the track of the system, which will depend on how the post-tropical cyclone interacts with a mid-tropospheric cutoff low that develops over the northeastern United States. The new official forecast keeps the cyclone closer to the east coast from 72-120 hours in deference to the latest GFS solution. It is important not to focus on the forecast landfall point of this system. In addition to the normal uncertainty in track and intensity forecasts, dangerous storm surge flooding is likely to extend along the Gulf coast well to the east and south of the path of the center. FORECAST POSITIONS AND MAX WINDS INIT 31/2100Z 25.5N 87.4W 40 KT 45 MPH 12H 01/0600Z 26.5N 87.3W 45 KT 50 MPH 24H 01/1800Z 28.1N 86.3W 50 KT 60 MPH 36H 02/0600Z 30.0N 85.0W 60 KT 70 MPH 48H 02/1800Z 32.0N 82.9W 50 KT 60 MPH...INLAND 72H 03/1800Z 36.5N 77.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 04/1800Z 39.0N 74.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 05/1800Z 39.5N 72.0W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch
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