Somewhat unexpectedly, Hurricane Florence rapidly intensified into the first major hurricane of the 2018 Atlantic hurricane season Wednesday morning, and has since strengthened into a Category 4 hurricane. Last night, Tropical Storm Gordon made landfall near the Alabama-Mississippi border as a strong tropical storm with maximum sustained winds of 70 mph, and has rapidly weakened to a tropical depression today. There is also Invest 92L to watch in the eastern Atlantic, which is likely to become a tropical depression by Friday as it moves westward to west-northwestward.

Florence becomes the Atlantic’s first major hurricane of 2018

Over the open Atlantic, Hurricane Florence has become a Category 4 hurricane. As of 5:00 p.m. EDT Wednesday, Hurricane Florence was centered near 22.7°N 46.6°W, and was moving northwestward at about 13 mph. Maximum sustained winds were 115 knots (130 mph), with an estimated minimum pressure of 953 mb. It is remarkable that Florence has strengthened into a Category 4 hurricane, since it was not predicted by models and southwesterly shear of over 15 knots is analyzed over the hurricane. Due to the shear, nearly all of the models predict that Florence will weaken some during the next 48 hours or so. Even though Florence has held up against the wind shear quite well, it is likely that an eyewall replacement cycle will begin soon, which would also cause weakening. Regardless, Florence is likely to remain a hurricane for the next several days as it tracks west-northwestward to northwestward. It is too soon to determine if Florence will affect the United States, though it certainly cannot be ruled out at this stage based on recent model guidance. Normally, an Atlantic hurricane this far north and east would recurve out to sea, but the steering pattern is more complex than usual due to a strong ridge of high pressure over the Northeastern United States expected to build. Bermuda is more likely to be directly affected by Florence, and both the GFS and ECMWF models predict that Florence will be just south of the small island in about six days. Florence will need to be monitored closely over the coming days.

Florence is the easternmost Atlantic Category 4 hurricane since Hurricane Julia in 2010. It also became a major hurricane very near the average first Atlantic major hurricane’s date of formation, which is September 4.

Gordon now inland as a weakening tropical depression

Tropical Storm Gordon made landfall at about 10:30 p.m. CDT (11:30 p.m. EDT) Tuesday near the Alabama-Mississippi border, with maximum sustained winds of 60 knots (70 mph) and an estimated minimum pressure of 997 mb. Since that time, Gordon has weakened quickly, and is now a tropical depression over central Mississippi. As of 4:00 p.m. CDT (5:00 p.m. EDT) Wednesday, Tropical Depression Gordon was centered near 32.8°N 90.7°W, and was moving northwestward at about 9 mph. Maximum sustained winds were 25 knots (30 mph), with an estimated minimum pressure of 1012 mb. Gordon is expected to continue weakening as it moves northwestward farther inland, and is likely to become a remnant low by Friday. All watches and warnings have been discontinued, though Gordon is expected to bring showers and thunderstorms in its path. An isolated tornado is also possible. Gordon’s remnants should become extratropical this weekend.

Invest 92L expected to develop, wave behind 92L may also develop

A broad area of low pressure a few hundred miles southwest of the Cabo Verde Islands – designated Invest 92L – is gradually becoming better organized, and a tropical depression is expected to form by the end of the week. As of 18:00 UTC Wednesday, 92L was located near 12.2°N 28.1°W, and was moving slowly west-northwestward. Maximum sustained winds were 25 knots (30 mph), with an estimated minimum pressure of 1007 mb. The National Hurricane Center (NHC) gives 92L a 70 percent chance of development within 48 hours, and a 90 percent chance within five days. Conditions are expected to be favorable for development, with wind shear decreasing to less than 10 knots by 36 hours, and sea surface temperatures are expected to remain above 26.5°C (79.7°F) for the next five days. All of the reliable global models in their 12z Wednesday runs, including the GFS, ECMWF and UKMET, predicted that 92L would develop into a tropical cyclone. It is possible 92L could affect the Lesser Antilles, and these islands will need to monitor 92L closely. Since it has not developed into a tropical cyclone, it is too soon to speculate the future track and intensity of 92L, though it is likely at least a tropical storm will develop over the central tropical Atlantic.

A tropical wave is also expected to exit the coast of west Africa on Friday or Saturday, and this wave could develop over the eastern tropical Atlantic by early next week. The NHC gives this system a near zero percent chance of development within 48 hours, but a 30 percent chance within five days. The 12z Wednesday ECMWF model predicted that this wave would develop into a tropical cyclone, while the GFS and UKMET models did not show development. It is possible that this system could interact with 92L if it develops, and this could influence the future track of 92L. Most likely, if this wave develops, it would not pose a threat to any land areas, with the exception of possibly the Cabo Verde islands. The next two names on the Atlantic naming list are Helene and Isaac.