Busy North Atlantic Tropics

North Atlantic is Warmer, More SEP/OCT Hurricanes
09/04/2018, 8:22 am EDT
Very Warm Water Surface Ahead of Florence
09/08/2018, 12:19 pm EDT
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Florence has weakened dramatically due to westerly shear

Florence tracks westward into a warmer ocean/no shear zone

Returns to major hurricane status early next week

Uncertainty: Florence into Carolinas or stall off coast

92L and 93L both likely to become hurricanes

Climate Impact Company Tropical Cyclone Risk Table

EventProbability

Tropical

Storm (previous)

Probability Hurricane (previous)Probability Intense Hurricane (previous)U.S. East Coast Strike (previous)Gulf of Mexico Strike (previous)
Hurricane Florence100% (100%)100%

(100%)

100%

(15%)

45%

(25%)

0%

(0%)

Disturbance 92L90%

(80%)

50%

(35%)

10%

(5%)

5%

(5%)

10%

(3%)

Disturbance 93L90%40%5%3%1%

 Table 1: Climate Impact tropical cyclone risk forecast table.

Fig. 1: The axis of upper shear axis. Note little or no shear ahead for Florence once past westerly shear across storm now.

Fig. 2: Florence is headed for an exceptionally warm ocean surface next week.

Discussion: At 5 AM EDT Tropical Storm Florence was located at 25.1 North/50.7 West or about 925 miles east-northeast of the Leeward Islands. Florence is moving west at 7 mph with top wind 65 mph and surface pressure 996 MB. Florence has weakened considerably due to westerly shear across the storm the past 12-18 hours.

Florence is forecast to drift west slowly returning to hurricane strength the second half of the weekend as the upper shear eases. NOAA/NHC forecasts Florence to return to major hurricane classification in 4-5 days as upper shear fades and Florence tracks over warm surface water.

The 6-10 day forecast is critical and made with low confidence. Potential scenarios include a major hurricane into the upper South Carolina coast Thursday (ECM model) or a north turn but stalling south of Long Island for 2-3 days late next week (GFS model).

Tropical Disturbance 92L is located in the east-central North Atlantic tropics while Tropical Disturbance 93L is approaching the Cape Verde Islands. Both of these systems are likely to become tropical storms within 1-2 days. There is likelihood that each become hurricanes in 4-5 days. 92L will head west for the Caribbean Sea while 93L is likely to turn northwest toward the central subtropical North Atlantic in 5 days. The next storm names are Helene and Isaac.

Fig. 3: NOAA/NHC 5-day forecast track of Florence.

Fig. 4: The ECMWF 10-day forecast track for Florence.