DISCUSSION (Source Aon Cat Alert Research)
Hurricane Florence, located approximately 385 miles (615 kilometers) southeast of Wilmington, North Carolina, is currently tracking northwest at 16 mph (26 kph). Data from an Air Force Reserve Hurricane Hunter aircraft along with satellite imagery and various intensity estimates indicate that Florence has weakened instead of strengthening. However, while the hurricane hasn’t strengthened in terms of peak winds, the inner-core and outer wind fields have continued to expand. This has resulted in an overall increase in Florence’s total energy, which will create a significant storm surge event. The upper-level outflow remains impressive and is still expanding except on the southern side.
Florence is moving toward the northwest, and the newest model guidance has come together in much better agreement on the storm moving northwestward around a strong ridge of high pressure located between Bermuda and the U.S. Mid-Atlantic region for the next 48 hours. At that time, Florence is forecast to approach the southern portion of the North Carolina coast, then slow down considerably and turn westward within collapsing steering flow. A very slow westward motion near the coasts of North and South Carolina is expected to continue into Friday and Saturday. There remain some differences in the model track forecasts, and the NHC has made only a slight eastward shift in the forecast track through 36 hours. At 48 hours and beyond, the NHC did not make any significant changes to the previous track, which still shows Florence moving slowly westward across South Carolina and western North Carolina on Day 4, followed by a slow northward motion up the Appalachian mountain chain on Day 5.
A narrow window of opportunity remains during the next 24 hours for Florence to strengthen a little when the hurricane passes over the warmer sea surface temperatures and deeper warm water (higher upper-ocean heat content) associated with the Gulf Stream. Low vertical wind shear will also be present that could aid in any strengthening process. However, significant strengthening is not anticipated due to Florence’s large and expanding inner-core wind field. By 36 hours and beyond, decreasing ocean heat content along with the slowing forward speed of Florence will likely produce cold upwelling beneath the hurricane, inducing a gradual weakening trend. When Florence moves over the shallow coastal shelf waters in the next 48-72 hours, land interaction and more significant upwelling are anticipated, which should further enhance the weakening process. The NHC intensity forecast remains near the higher statistical guidance through 48 hours, then follows the rest of the model trends after that time.
The NHC states that although the maximum winds are expected to weaken a little more, Florence 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 from the National Hurricane Center
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 prolonged significant river flooding are likely over portions of the Carolinas and the southern and central Appalachians 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, 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.