NOAA indicates Florence rolls westward and becomes a major hurricane targeting the South Carolina coast late Thursday.
84-86F surface water ahead of Florence, supports cat-4/cat-5 hurricane (if no shear)
Fig. 1: The North Atlantic Basin satellite view with storm tracks as forecast by NOAA/NHC.
Discussion: The North Atlantic basin has become busy with 4 systems to follow as the peak of season (Sep. 11) arrives. All eyes are on Tropical Storm Florence heading for warmer waters and a low shear environment which should easily allow Florence to regain major hurricane status. The NOAA/NHC forecast indicates a category 4 hurricane approaching the South Carolina coast Thursday night.
At 11 AM EDT Tropical Storm Florence was located at 24.5N/54.3W or about 835 miles southeast of Bermuda. Florence is moving west at 7 mph with top wind near 65 mph. Surface pressure is 995 MB. Florence is beginning to regain strength. The outlook indicates Florence returns to hurricane force tomorrow and major hurricane intensity by early Monday. As Florence travels westward upper shear eases and passage across anomalous warm water assures strengthening. Tropical Disturbance 94L also strengthens. The heat emitted by convection associated with 94L should strengthen the subtropical ridge to the east maintaining a westerly steering current for Florence. 94L is not expected to become a tropical cyclone BUT its interaction with Florence likely determines how long Florence travels westward before any northwest turn. The farther west track (rather than a northward turn) is the most correct track (for now) and offered by the ECM (model) and also preferred in the NOAA/NHC track. Its possible Florence may travel farther west before turning northwest. The water temperatures are very warm and intensification to a category 4 hurricane is confident. For the moment, South Carolina appears the target of a category 4 hurricane next late Thursday. Effects by Florence including wind, rain and sea conditions will affect the entire East Coast.
Tropical Storm Helene is in the Cape Verde Islands and forecast to travel westward gaining hurricane strength later tomorrow. Helene turns northwestward and may encounter upper westerly shear in 5 days in the subtropical North Atlantic (plus cooler water upwelled by Florence) and weaken to a tropical storm. Forecast models keep Helene out-to-sea.
Tropical Depression 9 is moving west and should reach the Caribbean Sea in 5-6 days. NOAA/NHC indicates a hurricane at that time although the intensity forecast has eased back in the latest forecast update. Presence of a strong –QBO could inhibit hurricane intensity of this system given the expected low latitude track through the southeast/south Caribbean Sea.
Climate Impact Company Tropical Cyclone Risk Table
|Probability Hurricane (previous)||Probability Intense Hurricane (previous)||U.S. East Coast Strike (previous)||Gulf of Mexico Strike (previous)|
|T.S. Florence||100% (100%)||100%|
|Tropical Dep 9||90%|
Table 1: Climate Impact tropical cyclone risk forecast table.
Fig. 2: NOAA/NHC 5-day forecast track of Florence with ECM/GFS day 6-7 forecast tracks added.
Fig. 3: Tropical cyclone model forecast tracks for Florence out to 5 days.
Fig. 4: Tropical cyclone model forecast intensity for Florence out to 5 days.
Fig. 5: ECMWF 10-day forecast track for Florence.
Fig. 6: North Atlantic sea surface temperature analysis indicates very warm surface water is ahead for Florence.
Fig. 7: NOAA/WPC projects the heavy rain profile (and likely strongest wind) for days 6-7 (THU/FRI) associated with Florence. Amount forecast is likely to increase and a slight south shift may occur as well.