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Tropical Storm Florence Forecast Discussion Number 63
2018-09-15 04:43:02| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Fri Sep 14 2018 573 WTNT41 KNHC 150242 TCDAT1 Tropical Storm Florence Discussion Number 63 NWS National Hurricane Center Miami FL AL062018 1100 PM EDT Fri Sep 14 2018 Although we lost data from the Wilmington, North Carolina, WSR-88D radar several hours ago, the radars from Raleigh and Columbia have clearly shown Florence's center has moved into extreme eastern South Carolina. Reflectivities around the eye have been decreasing, but there are still some strong spiral bands moving from southeast to northwest across portions of southeastern North Carolina. Maximum Doppler velocities are 65-70 kt from 5000-7000 feet, and on this basis Florence's maximum surface winds are estimated to be 55 kt. Radar fixes indicate that Florence has turned west-southwestward and has an initial motion of 255/4 kt. A mid-level high centered near Iowa and Missouri is expected to slide eastward to the north of Florence over the next 48 hours, which should cause the storm to maintain a slow motion and gradually turn toward the west and northwest over the Carolinas. For this period, the new official forecast track has been shifted a bit southward to follow an overall trend in the model guidance, but this isn't surprising given what some of the models were showing last night. After 48 hours, Florence is expected to get picked up by the mid-latitude westerlies, accelerating north and northeastward to the western Atlantic by day 5. The NHC track forecast is fairly close to the TVCN multi-model consensus and just a little south of the previous forecast beyond 72 hours. Florence's winds should continue to slowly decay as the center ambles farther inland, but enough of the circulation should remain over water to allow the cyclone to remain as a tropical storm for the next 24 hours or so. This thinking follows the global model fields of the GFS and ECMWF models. After 24 hours, most of Florence's circulation should be inland, allowing the cyclone to weaken to a tropical depression and eventually degenerate into a remnant low over the Ohio Valley by day 3. The remnant low is then likely to become an extratropical low by day 4, and it forecast to begin producing gale-force winds well east of New England to the south of Atlantic Canada. Although coastal storm surge flooding will gradually subside tonight and Saturday, it cannot be emphasized enough that another serious hazard associated with slow-moving Florence will continue to be extremely heavy rainfall. More than a foot of rain has already fallen across portions of southeastern North Carolina, and more rain is still to come, which will cause disastrous flooding that will spread inland through the weekend. Key Messages: 1. Life-threatening storm surge will continue along portions of the North Carolina coast through tonight, and also along the Neuse and Pamlico Rivers in western Pamlico Sound, where rainfall and freshwater flooding will also contribute to high water levels. Dangerous storm surge could also affect portions of the northeast coast of South Carolina coast tonight. 2. Life-threatening, catastrophic flash floods and prolonged significant river flooding are likely over portions of the Carolinas and the southern to central Appalachians from western North Carolina into southwest Virginia through early next week, as Florence moves slowly inland. In addition to the flash flood and flooding threat, landslides are also possible in the higher terrain of the southern and central Appalachians across western North Carolina into southwest Virginia. 3. Tropical storm conditions will continue along the coast within the tropical storm warning area and also well inland across portions of South Carolina and North Carolina through Saturday. 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 15/0300Z 33.8N 79.1W 55 KT 65 MPH...INLAND 12H 15/1200Z 33.7N 79.6W 45 KT 50 MPH...INLAND 24H 16/0000Z 33.8N 80.5W 35 KT 40 MPH...INLAND 36H 16/1200Z 34.4N 81.8W 30 KT 35 MPH...INLAND 48H 17/0000Z 35.9N 83.1W 25 KT 30 MPH...INLAND 72H 18/0000Z 39.3N 81.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 19/0000Z 41.0N 74.0W 30 KT 35 MPH...POST-TROP/EXTRATROP 120H 20/0000Z 43.5N 61.0W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Berg
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