Issued at 1100 AM EDT Wed Sep 12 2018 779 WTNT41 KNHC 121456 TCDAT1 Hurricane Florence Discussion Number 53 NWS National Hurricane Center Miami FL AL062018 1100 AM EDT Wed Sep 12 2018 An Air Force Reserve hurricane hunter aircraft investigating Florence this morning has found no change in the hurricane's peak intensity of 115 kt, even though the central pressure had decreased a few millibars down to 943 mb.
However, the aircraft data do indicate that Florence's inner-core wind field has expanded, with the 50-kt wind radii now extending outward up to 100 n mi to the northeast.
Florence still has a very distinct eye in satellite imagery, but cloud top temperatures have been waxing and waning in the eyewall region, with slight downward trend noted in the past hour or so. In contrast, the upper-level outflow remains impressive and continues to expand everywhere except to the south.
Florence is now moving toward the northwest or 305/13 kt. There has been no significant change to the NHC model guidance, including the corrected-consensus models HCCA and FSSE, which are now virtually on top of each other and the simple consensus model TVCA.
As a result, no changes were required to the previous NHC track. The shortwave trough over the southern Plains seen in water vapor imagery could end up being a significant factor as it rounds the narrow ridge over the Tennessee Valley and is expected to erode the ridge along the U.S. mid-Atlantic coast on days 3-5.
At this time, little change has been made to the NHC track forecast, which remains very close to the aforementioned consensus aids through 72 hours. On the current forecast track, the center of Florence is expected to be near the coasts of southern North Carolina and northern South Carolina in 48 to 72 hours and then drift westward to west- southwestward in weak steering flow.
There is still a narrow window of opportunity for Florence to strengthen a little when the cyclone moves over the warmest SSTs and highest upper-ocean heat content while the shear will be the lowest between 0600-1200 UTC tomorrow morning. After that, decreasing ocean heat content along with the slowing forward speed of Florence should cause at least some cold upwelling beneath the hurricane, which should induce a gradual weakening trend.
Once Florence reaches the shallow coastal shelf waters in 72 h, land interaction and more significant upwelling are expected, further enhancing the weakening process. The NHC intensity forecast remains near the higher statistical guidance through 48 hours, then follows the trend of the decay SHIPS model after that time.
While Florence's maximum winds are expected to weaken a little, it is still expected to remain a dangerous major hurricane as it approaches the coast. The threat to life from storm surge and rainfall will not diminish, and these impacts will cover a large area regardless of exactly where the center of Florence moves. Key Messages:
1. A life-threatening storm surge is now 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. All interests in these areas should complete preparations and follow any advice given by local officials.
2. Life-threatening, catastrophic flash flooding and significant river flooding is likely over portions of the Carolinas late this week into 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, and a Hurricane Warning is in effect. Strong winds could also spread inland into portions of the Carolinas. 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 12/1500Z 29.8N 71.3W 115 KT 130 MPH 12H 13/0000Z 31.1N 73.1W 120 KT 140 MPH 24H 13/1200Z 32.6N 75.1W 125 KT 145 MPH 36H 14/0000Z 33.5N 76.5W 120 KT 140 MPH 48H 14/1200Z 33.8N 77.4W 105 KT 120 MPH...NEAR THE COAST 72H 15/1200Z 33.6N 78.4W 85 KT 100 MPH...NEAR THE COAST 96H 16/1200Z 33.6N 80.4W 45 KT 50 MPH...INLAND 120H 17/1200Z 34.7N 82.8W 25 KT 30 MPH...INLAND
Forecaster Stewart
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