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| #939431 (Received by flhurricane at: 11:00 PM 10.Sep.2018) TCDAT1 Hurricane Florence Discussion Number 47 NWS National Hurricane Center Miami FL AL062018 1100 PM AST Mon Sep 10 2018 The rapid intensification of Florence ended just after the last advisory, with the central pressure falling to near 939 mb. Since that time, the eyewall convection has become a bit ragged and the latest central pressure from the Air Force Reserve Hurricane Hunter aircraft is near 944 mb. The initial intensity will remain a possibly generous 120 kt for this advisory based on the aircraft winds. Microwave imagery suggests that Florence may be starting an eyewall replacement cycle. However, the winds from the Hurricane Hunter did not clearly indicate the presence of an outer eyewall. Florence should remain in a light shear environment and over sea surface temperatures near 29C for at least the next 48 h. Thus, there is little other than eyewall replacement cycles to keep the hurricane from intensifying further as indicated by all of the intensity guidance. The new intensity forecast calls for continued strengthening to near category 5 strength, although at a slower rate than what occurred during the last 30 h. Florence is expected to encounter southwesterly shear near the 72 h point, which could cause slight weakening before landfall. However, there remains high confidence that Florence will be a large and extremely dangerous hurricane, regardless of its exact intensity. The initial motion is 290/11. A building mid-level ridge over the northwestern Atlantic is expected to steer Florence west-northwestward to northwestward with an increase in forward speed during the next 48 h. After that time, a marked decrease in forward speed is likely as another ridge builds over the Great Lakes to the north of Florence. The track guidance continues to show some spread between the ECMWF on the left side of the envelope and the GFS on the right side. Overall, though, the guidance has again shifted a little to the right, and the 72-96 h points are nudged just a little to the right from the previous forecast. It is important not to focus on the exact forecast track as average NHC errors at days 3, 4, and 5 are about 100, 140 and 180 n mi, respectively, and dangerous hazards will extend well away from the center. The NOAA G-IV jet will continue to conduct synoptic surveillance missions every 12 h through at least Wednesday. In addition, special 0600 UTC and 1800 UTC radiosonde launches have been expanded to additional upper-air stations across the U.S. to collect extra data for the numerical models. The next Air Force Reserve Hurricane Hunter mission into Florence is scheduled for near 12Z. Key Messages: 1. A life-threatening storm surge is likely along portions of the coastlines of South Carolina, North Carolina, and Virginia, and a Storm Surge Watch will likely be issued for some of these areas by Tuesday morning. All interests from South Carolina into the mid- Atlantic region should ensure they have their hurricane plan in place and follow any advice given by local officials. 2. Life-threatening freshwater flooding is likely from a prolonged and exceptionally heavy rainfall event, which may extend inland over the Carolinas and Mid Atlantic for hundreds of miles 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, and a Hurricane Watch will likely be issued by Tuesday morning. Damaging winds could also spread well inland into portions of the Carolinas and Virginia. 4. Large swells affecting Bermuda and portions of the U.S. East Coast will continue this week, resulting in life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 11/0300Z 25.9N 62.4W 120 KT 140 MPH 12H 11/1200Z 26.5N 64.5W 125 KT 145 MPH 24H 12/0000Z 27.9N 67.5W 130 KT 150 MPH 36H 12/1200Z 29.6N 70.4W 135 KT 155 MPH 48H 13/0000Z 31.3N 73.2W 130 KT 150 MPH 72H 14/0000Z 34.0N 76.5W 120 KT 140 MPH 96H 15/0000Z 35.5N 78.0W 50 KT 60 MPH...INLAND 120H 16/0000Z 36.5N 79.0W 25 KT 30 MPH...INLAND $$ Forecaster Beven |
