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Tropical Storm Florence Forecast Discussion Number 62
2018-09-15 00:19:15| National Hurricane Center (Atlantic)
Issued at 500 PM EDT Fri Sep 14 2018 ZCZC MIATCDAT1 ALL TTAA00 KNHC DDHHMM Tropical Storm Florence Discussion Number 62 NWS National Hurricane Center Miami FL AL062018 500 PM EDT Fri Sep 14 2018 Florence's satellite appearance continues to be quite impressive with well-established outflow and a nearly symmetrical cloud pattern. In radar imagery, however, the inner-core convection has continued to weaken and the echoes are now more stratiform in nature, while outer banding remains rather vigorous, especially south of Cape Lookout and Morehead City, North Carolina. An eye is no longer evident, and the pressure has continued to rise to a now estimated to be 972 mb based on nearby surface observations. Air Force Reserve aircraft data, NOAA Doppler weather radar velocity data from Wilmington, and nearby surface observations indicate that Florence's intensity has decreased to 60 kt, tropical storm status. Florence has turned westward and the motion estimate is now 270/03 kt. The new 1200Z global and regional model guidance is in good agreement on Florence moving slowly in a general westward direction for the next 48 hours or so, followed by a northward motion on day 3 as the system moves around the western periphery of a narrow subtropical ridge. On days 4 and 5, the cyclone is forecast to turn northeastward and accelerate ahead of an approaching shortwave trough and frontal system, and emerge off the northeast U.S. coast as an extratropical low. The new official forecast track is very similar to the previous advisory, and is lies near the northern and eastern edge of model guidance envelope, is closer to the TVCA/TVCN consensus models. Florence is expected to only slowly weaken overnight due to its proximity to the warm Atlantic where convective bands are expected to continue to develop and propagate inland in the eastern and southern portion of the circulation, which will act to bring down some of the stronger winds aloft. It is worth noting that the last reconnaissance pass indicated 700-mb flight-level winds of 77 kt just east of Charleston, South Carolina, so it won't take much convection to bring down some of those stronger winds to the surface as gusts. More rapid weakening is forecast over the weekend as Florence moves westward across the higher terrain of central and northwestern South Carolina. The official intensity forecast follows the weakening trend of the previous advisory, and is similar to an average of the GFS- and ECMWF-based Decay SHIPS models. 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 16 inches of rain has already fallen in many areas across 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, mudslides 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. 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 14/2100Z 34.0N 78.6W 60 KT 70 MPH...INLAND 12H 15/0600Z 33.9N 79.3W 50 KT 60 MPH...INLAND 24H 15/1800Z 33.9N 80.3W 40 KT 45 MPH...INLAND 36H 16/0600Z 34.4N 81.4W 25 KT 30 MPH...INLAND 48H 16/1800Z 35.5N 82.6W 25 KT 30 MPH...INLAND 72H 17/1800Z 38.5N 82.6W 20 KT 25 MPH...POST-TROP/INLAND 96H 18/1800Z 41.5N 76.0W 20 KT 25 MPH...POST-TROP/INLAND 120H 19/1800Z 44.0N 64.5W 30 KT 35 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart NNNN
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