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Post-Tropical Cyclone Nestor Forecast Discussion Number 9
2019-10-19 16:58:40| National Hurricane Center (Atlantic)
Issued at 1000 AM CDT Sat Oct 19 2019 000 WTNT41 KNHC 191458 TCDAT1 Post-Tropical Cyclone Nestor Discussion Number 9 NWS National Hurricane Center Miami FL AL162019 1000 AM CDT Sat Oct 19 2019 Nestor has made the transition to a post-tropical extratropical cyclone. There has been no significant convection near the low-level center for more than six hours, and satellite and surface observations indicate that the cyclone's center has merged with a nearby frontal system that lies along the coast of the Florida panhandle. The overall cloud pattern more closely resembles that of an occluded low pressure system now, including a pre-frontal squall line or convergence zone a few hundred nmi east of the low. Sustained tropical-storm-force winds with gusts to near 50 kt have been reported by some of the buoys and coastal marine stations over the northeastern Gulf of Mexico during the past few hours. The initial intensity of 45 kt is based on Doppler velocity values of 50-55 kt between 4000-6000 ft ASL located over Apalachee Bay, which approximately equals surface winds of 40-44 kt. The now well-defined low-level center made a brief jog toward the northwest early this morning as an upper-level low passed over the larger cyclonic gyre. However, the motion since that time has been slowly eastward, and the initial motion estimate is now east-northeastward or 075/08 kt. Despite the earlier erratic motion, the latest NHC track model guidance remains in very good agreement on post-tropical Nestor moving northeastward and accelerating over the next 36 hours or so, followed by a turn toward the east once the cyclone reaches the North Carolina Outer Banks. By 48 hours, the parent upper-level low is expected to weaken and open up into a shortwave trough, and leave Nestor behind as a weakening extratropical cyclone that dissipates by 96 h east of the U.S. east coast. The new official forecast track was only nudged a little to the west of the previous advisory due to the more westward initial position, and lies close to an average of the deterministic 0000 UTC and 0600Z GFS, ECMWF, and UKMET model runs. No strengthening is anticipated before Nestor moves inland later this afternoon. Some slight weakening will occur after the center moves inland, but gale-force winds are expected develop over the Atlantic waters of northeastern Florida to the Carolinas this afternoon and tonight, and across the mid-Atlantic U.S. coastal waters on Sunday. The extratropical cyclone is expected to dissipate or merge with a cold front in about 4 days or sooner. Given the non-tropical structure of Nestor, dangerous storm surge and tropical-storm-force and gale-force winds will occur along a large portion of the Florida Gulf Coast well east of the track of Nestor's center today. Key Messages: 1. There is a danger of life-threatening storm surge inundation of up to 4 feet above ground level along the Florida Gulf Coast from Indian Pass to Clearwater Beach, where a Storm Surge Warning is in effect. Residents in these areas should follow advice given by local officials. 2. Tropical storm force winds will continue across portions of the Florida Gulf Coast, where tropical storm warnings are in effect. Regardless of the exact track and intensity of the system, these winds will cover a large area, especially east of the center. 3. Isolated flash flooding is possible across the southeastern United States into Sunday morning. 4. Wind and coastal flooding hazards along the U.S. East Coast will be covered by non-tropical watches and warnings issued by local NWS offices, since the system is expected to lose its tropical characteristics after it moves inland along the Gulf Coast. FORECAST POSITIONS AND MAX WINDS INIT 19/1500Z 29.3N 86.3W 45 KT 50 MPH...POST-TROP/EXTRATROP 12H 20/0000Z 31.0N 83.5W 35 KT 40 MPH...POST-TROP/EXTRATROP 24H 20/1200Z 34.1N 79.5W 40 KT 45 MPH...POST-TROP/EXTRATROP 36H 21/0000Z 36.0N 75.1W 40 KT 45 MPH...POST-TROP/EXTRATROP 48H 21/1200Z 36.6N 71.5W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 22/1200Z 36.4N 66.6W 35 KT 40 MPH...POST-TROP/EXTRATROP 96H 23/1200Z...DISSIPATED $$ Forecaster Stewart
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