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| #940447 (Received by flhurricane at: 5:03 PM 15.Sep.2018) TCDAT1 Tropical Storm Florence Discussion Number 66 NWS National Hurricane Center Miami FL AL062018 500 PM EDT Sat Sep 15 2018 Florence`s center has continued its slow...and I do mean s-l-o-w... westward trek across eastern South Carolina, with little change in the overall structure of the wind field both overland and over water. NOAA WSR-88D Doppler weather radar data, surface observations, and a 1527Z ASCAT pass indicate that Florence is still producing a significant fetch of tropical storm force winds within and adjacent to the the two bands of convection that are currently located between the Cape Fear/Wilmington area and Bogue Inlet, North Carolina. The ASCAT pass contained numerous 40-45 kt wind vectors, and the NOAA NOS observing site at Johnny Mercer Pier in Wrightsville Beach, North Carolina, has been reporting sustained winds of 38-41 kt and gusts to 46-48 kt during the past few hours during the passage of light to moderate rain showers. Therefore, the initial intensity is being maintained at a conservative 40 kt for this advisory. The estimated central pressure of 997 mb is based on nearby surface observations across eastern South Carolina. The initial motion remains 270/02 kt. The new 12Z model guidance remains in excellent agreement on a mid-level ridge currently to the northwest and north of Florence moving steadily eastward during the next 48 hours, which will keep the broad cyclone moving slowly westward to west-northwestward during that time. By 48 hours and beyond, the ridge is forecast to continue to shift eastward to near the northeast U.S. coast and weaken, which will allow Florence and its remnant circulation to move slowly northward into the mid-latitude westerlies by Tuesday. By days 3-5, the global models diverge on where and how fast Florence`s then extratropical circulation moves. Due to the significant spread in the guidance, the official forecast track lies close to the consensus model TCVA/TVCN and the previous advisory track forecast. Florence`s inner-core convection and wind field will steadily weaken throughout the next 48 hours or so. However, the outer wind field and an associated band of deep convection in the eastern semicircle should continue to produce tropical-storm-force winds for another 12 hours or so over water and near the coast, with occasional strong wind gusts occurring over land. The official intensity forecast is close to an average of the Decay-SHIPS and LGEM, and the IVCN consensus intensity model guidance through 72 hours, and then follows a blend of the IVCN, HCCA, and FSSE consensus models at 96 and 120 hours when the post-tropical cyclone moves back over water and strengthens some due to baroclinic processes. Although coastal storm surge flooding will continue to subside tonight and Sunday, torrential rainfall will continue to be a serious hazard associated with slow-moving Florence. More than two- and-a-half feet 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 farther inland through the weekend. Key Messages: 1. 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 west-central Virginia and far eastern West 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. 2. Water levels along the coast will gradually subside through Sunday. 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 today. 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 15/2100Z 33.6N 79.9W 40 KT 45 MPH...INLAND 12H 16/0600Z 33.9N 80.9W 35 KT 40 MPH...INLAND 24H 16/1800Z 35.1N 82.6W 25 KT 30 MPH...INLAND 36H 17/0600Z 37.0N 83.2W 25 KT 30 MPH...INLAND 48H 17/1800Z 38.8N 82.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 18/1800Z 41.4N 74.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 19/1800Z 43.3N 60.8W 30 KT 35 MPH...POST-TROP/EXTRATROP 120H 20/1800Z 47.0N 47.0W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart |
