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Hurricane Florence Forecast Discussion Number 57
2018-09-13 16:56:19| National Hurricane Center (Atlantic)
Issued at 1100 AM EDT Thu Sep 13 2018 236 WTNT41 KNHC 131456 TCDAT1 Hurricane Florence Discussion Number 57 NWS National Hurricane Center Miami FL AL062018 1100 AM EDT Thu Sep 13 2018 The satellite and radar presentations of Florence have improved somewhat this morning, with a 20-25 nmi wide eye closing off in the radar data from the Morehead City and Wilmington WSR-88D Doppler weather radars. However, an Air Force Reserve reconnaissance aircraft investigating the hurricane this morning has not yet found any flight-level or SFMR winds to support more than about 80 kt at the surface thus far, even though the pressure has decreased to 955 mb. The initial intensity has only been lowered to 90 kt, given that there are peak Doppler velocity values up to 110 kt with average values of 95-97 kt at 15,000 ft in the northern eyewall region, an area of the hurricane that the reconnaissance aircraft has not yet sampled. The upper-level outflow pattern remains quite impressive. Florence has been gradually slowing down this morning, and the initial motion estimate is now 315/09 kt. The subtropical ridge to the northeast and east of Florence is now well-established between Bermuda and the U.S. mid-Atlantic region and extends westward into Virginia and the central Appalachians. This large-scale feature is expected to keep the hurricane moving northwestward today, followed by a turn toward the west at a much slower speed on Friday as the ridge to the north of Florence weakens due to a weak shortwave trough dropping slowly southward from the Ohio Valley. On days 3-5, Florence is forecast turn toward the northwest and north around the western periphery of the subtropical ridge, and move across western South Carolina on Sunday, across western North Carolina and eastern Tennessee on Monday, and then move up the spine of the Appalachians as an extratropical low after the cyclone merges or interacts with a frontal system. The new NHC forecast track is similar to the previous one, and lies close to a blend of the consensus models TVCA, HCCA, and FSSE. Florence is currently approaching the Gulfstream current, and the hurricane is forecast to move over warmer and deeper waters in 6-12 hours, which could allow for some slight strengthening. Just prior to landfall in about 24 hours, Florence is expected to weaken some due to upwelling of the shallow coastal waters. After landfall occurs, rapid weaning of the stronger inner-core wind field is expected to due land interaction and Florence's slow forward speed of 5 kt or less. However, intense rainbands are expected to develop over the Atlantic waters and keep moving along the coast and inland, likely producing strong wind gusts through Saturday night. Aircraft and satellite wind data show that Florence remains a large hurricane. Life-threatening storm surge, heavy rainfall, and damaging wind will cover a large area regardless of exactly where the center of Florence moves. Key Messages: 1. A life-threatening storm surge is now highly likely along portions of the coastlines of South Carolina and North Carolina, and a Storm Surge Warning is in effect for a portion of this area. The greatest storm surge inundation is expected between Cape Fear and Cape Hatteras, including the Neuse and Pamlico Rivers and western Pamlico Sound. 2. Life-threatening, catastrophic flash flooding and prolonged significant river flooding are likely over portions of the Carolinas and the southern and central Appalachians through early next week, as Florence is expected to slow down as it approaches the coast and moves inland. 3. Damaging hurricane-force winds are likely along portions of the coasts of South Carolina and North Carolina as soon as this evening, and a Hurricane Warning is in effect. Strong winds could also spread inland into portions of the Carolinas. 4. Large swells affecting Bermuda, portions of the U.S. East Coast, and the northwestern and central Bahamas will continue this week, resulting in life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 13/1500Z 33.4N 75.5W 90 KT 105 MPH 12H 14/0000Z 33.9N 76.6W 95 KT 110 MPH 24H 14/1200Z 34.2N 77.8W 85 KT 100 MPH...NEAR THE COAST 36H 15/0000Z 34.1N 78.7W 65 KT 75 MPH...INLAND 48H 15/1200Z 34.0N 79.6W 45 KT 50 MPH...INLAND 72H 16/1200Z 34.3N 81.8W 25 KT 30 MPH...INLAND 96H 17/1200Z 36.9N 83.0W 25 KT 30 MPH...INLAND 120H 18/1200Z 40.3N 79.2W 20 KT 25 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart
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