Due to strong wind shear, Hurricane Florence has become much less organized today, weakening into a Category 1 hurricane. Florence is likely to fall below hurricane strength tonight or early tomorrow, but is likely to begin restrengthening by Saturday as it enters a more favorable environment. Florence is expected to pass south of Bermuda next Tuesday, though direct impacts are still possible to the small island. It is a possibility that Florence could impact the United States East Coast, though confidence on Florence’s track beyond five days remains low. In addition to Florence, there are two other systems expected to become tropical cyclones: Invest 92L over the eastern tropical Atlantic, and Invest 93L over western Africa. In the eastern Pacific, Hurricane Olivia could potentially pose a long-range threat to the Hawaiian Islands from the east.

Florence weakens due to shear but expected to restrengthen, U.S. impacts still uncertain

As of 5:00 p.m. EDT Thursday, Hurricane Florence was centered near 25.0°N 49.6°W, and was moving northwestward at about 10 mph. Maximum sustained winds were 70 knots (80 mph), with an estimated minimum pressure of 989 mb. Although Florence was able to rapidly intensify yesterday in a small zone of lower shear, vertical wind shear near 25 knots (30 mph) has weakened Florence significantly, with the low-level center occasionally becoming exposed today. The shear is expected to lessen tomorrow, and remain low (less than 15 knots) for the next five days. Florence is also headed towards warmer waters near 29°C (84.2°F), and a slightly more moist environment. This should allow Florence to restrengthen, perhaps rapidly if it is able to quickly redevelop its inner core. The official National Hurricane Center (NHC) forecast brings Florence back up to Category 3 strength by Monday, though some of the guidance, such as the HWRF, bring Florence back to Category 4 strength. As a result, It is possible Florence could attain a new peak intensity in the western subtropical Atlantic.

Florence should generally continue on a westward motion through Sunday. After that time, Florence is expected to turn to the west-northwest, passing south of Bermuda on Tuesday. The eventual track of Florence remains quite uncertain in the medium range. The GFS and ECMWF models both bring Florence very close to the mid-Atlantic United States, with the GFS showing Florence remaining offshore as a powerful hurricane and the ECMWF showing Florence making landfall in the North Carolina Outer Banks. While most of the GEFS ensembles predict Florence will brush the coast without a landfall, many of the EPS ensembles predicted that the ridge of high pressure would remain strong and force Florence westward into the eastern U.S. The potential time of impact in the eastern United States would be about 7-8 days from now. Because of Florence’s high latitude, I do not expect it to reach the Bahamas or Gulf of Mexico. It is certainly possible that Florence turns to the northeast out to sea without making landfall in the U.S., or it could also pose a threat to Nova Scotia or Newfoundland. It should be stressed that the track of Florence is highly uncertain. If Florence does threaten the east coast, it is likely to be a powerful hurricane rather than a tropical storm, due to the expected favorable conditions in the subtropical western Atlantic. While there is no need to panic at this time, now is a great time to make sure you have a hurricane plan ready if you are in the path. Interests in Bermuda, the eastern United States, and Atlantic Canada should closely monitor the progress of Florence over the coming days.

Two new Atlantic tropical cyclones likely to develop this weekend

As Florence is expected to regain strength this weekend, two new tropical cyclones – Helene and Isaac – are likely to develop over the Atlantic’s Main Development Region (MDR).

The westernmost system, Invest 92L, is a broad area of low pressure that is gradually becoming better organized. As of 18:00 UTC Thursday, Invest 92L was located near 14.0°N 32.5°W, and was moving generally westward. Maximum sustained winds were 25 knots (30 mph), with an estimated minimum pressure of 1008 mb. The NHC gives 92L an 80 percent chance of development within 48 hours, and a 90 percent chance within five days. All of the reliable global models develop 92L into a tropical cyclone. Environmental conditions are expected to be quite favorable for development over the next five days, with warm water and wind shear below 10 knots. This should allow 92L to develop into a tropical depression by the weekend. 92L should generally move westward, and could pose a threat to the Lesser Antilles in about a week.

The easternmost system, Invest 93L, is a tropical wave currently over Western Africa. 93L is expected to develop into a tropical cyclone by Saturday, shortly after exiting the African coast. Global models are aggressive in developing 93L right after moving off Africa, and advisories could be initiated by NHC on a potential tropical cyclone tomorrow with tropical storm watches for the Cabo Verde Islands. 93L is expected to be in a moderate shear environment and over warm sea surface temperatures, which should allow 93L to develop. After affecting Cabo Verde, 93L should quickly turn to the northwest. Since 93L is already beginning to show signs of organization, it could develop before 92L.