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Hurricane Florence Forecast Discussion Number 58
2018-09-13 22:52:22| National Hurricane Center (Atlantic)
Issued at 500 PM EDT Thu Sep 13 2018 207 WTNT41 KNHC 132052 TCDAT1 Hurricane Florence Discussion Number 58 NWS National Hurricane Center Miami FL AL062018 500 PM EDT Thu Sep 13 2018 The satellite and radar presentations of Florence have changed little this afternoon with a 20-25 nmi wide eye waxing and waning as intrusions of dry air have occasionally eroded the southern and eastern eyewall. Despite the occasional ragged appearance of Florence's eye, reconnaissance aircraft data indicate that the central pressure has remained steady at 955 mb. The last reports from the Air Force Reserve hurricane hunters support an intensity of 85 kt, and this is corroborated by average Doppler velocity values of near 105 kt at 2500-3000 ft ASL. A report of a 10-minute average wind of 59 kt and a gust to 74 kt was recently received from the Cape Lookout C-MAN station (CLKN7). The 59-kt 10-minute wind speed is roughly equivalent to a 65-kt 1-minute wind. Florence has continued to slow down, and radar fixes over the past couple hours suggest that Florence has possibly stalled due to a re-organization of the eye/eyewall. Smoothing through the fixes over the past 6 h yields an initial motion estimate of 295/04 kt. There is no change to the previous forecast reasoning. The ridge to the north and east of Florence remains intact over the Atlantic Ocean, but water vapor imagery and special upper-air observations indicate that a shortwave trough has weakened that portion of the ridge along the U.S. mid-Atlantic coast, resulting in a weakening of the steering currents. The ridge is forecast by all of the latest model guidance to remain intact, albeit weak, for the next 72 hours, which will nudge Florence on a slow westward to west- southwest track into central South Carolina. On days 4 and 5, Florence is expected to become an extratropical low as it interacts with a front while moving northward and northeastward along the Appalachian Mountains. The official forecast track is similar to, but slightly south of the previous advisory track through 72 hours, with little change indicated on days 4 and 5. This scenario closely follows the simple consensus model TVCN/TVCA, which is north of the corrected-consensus models HCCA and FSSE, which are heavily weighing the southernmost model, ECMWF, which keeps Florence over or near the Atlantic through about 48 hours. Radar data indicate that Florence may be developing an outer eyewall. If this trend continues, then little change to the intensity is likely until landfall occurs in about 24 hours due in part to the low vertical wind shear conditions and the warm, deep waters of the Gulfstream current. Florence is expected to weaken after landfall, but the rate of weakening may be tempered somewhat due to much of the hurricane's circulation remaining over the warm waters of the Atlantic Ocean and Gulfstream. Once Florence moves farther inland over central South Carolina, rapid weakening of the inner-core wind field should occur due to land interaction and the cyclone's slow forward speed of 5 kt or less. However, intense rainbands are expected to continue developing 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 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 beginning 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 13/2100Z 33.7N 76.2W 85 KT 100 MPH 12H 14/0600Z 34.1N 77.2W 85 KT 100 MPH 24H 14/1800Z 34.2N 78.2W 75 KT 85 MPH...INLAND 36H 15/0600Z 33.9N 79.0W 50 KT 60 MPH...INLAND 48H 15/1800Z 33.8N 79.9W 35 KT 40 MPH...INLAND 72H 16/1800Z 34.8N 82.3W 25 KT 30 MPH...INLAND 96H 17/1800Z 37.9N 82.6W 20 KT 25 MPH...POST-TROP/INLAND 120H 18/1800Z 42.7N 76.3W 20 KT 25 MPH...POST-TROP/INLAND $$ Forecaster Stewart
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