Hurricane Irma has overall changed little in organization today, and is currently a Category 3 hurricane on the Saffir-Simpson Scale. A NOAA Hurricane Hunter reconnaissance aircraft investigated the hurricane Sunday afternoon, and found that its minimum pressure was a little lower than estimated, but maximum sustained winds remained about 115 mph. Irma is likely to pass over or just north of the Leeward Islands late Tuesday or early Wednesday, and Hurricane Watches have been issued for several of these islands. After that time, Irma is expected to continue on a west-northwestward path, and is likely to impact the Turks and Caicos Islands as well as The Bahamas by late this week. It is still too soon to determine how Irma will impact the United States, if at all, but residents of the Eastern United States should begin preparations.

As of 11:00 p.m. EDT Sunday, Hurricane Irma was centered near 17.2°N 51.0°W, and was moving west-southwestward at about 14 mph. Maximum sustained winds were 100 knots (115 mph), with a minimum pressure of 961 mb, based on aircraft data. Although the satellite appearance of Irma wasn’t very impressive a few hours ago, the eye has begun to become more distinct during the past few hours. Irma is likely to strengthen beginning on Monday, although the possibility of eyewall replacement cycles complicate the intensity forecast. Irma is expected to be in an environment of light to moderate wind shear, warming sea surface temperatures, and increasing mid-level moisture during the next five days. The official National Hurricane Center (NHC) forecast brings Irma to category 4 strength by Tuesday, while located just east of the Leeward Islands. Residents of the Leeward Islands should have their hurricane plan ready as Irma is likely to bring hurricane-force winds to the islands. A Hurricane Watch has been issued for the following islands: Antigua, Barbuda, Anguilla, Montserrat, St. Kitts, Saba, St. Eustatius, and Sint Maarten, Saint Martin and Saint Barthelemy.

After passing through or just north of the Leeward Islands, Irma is expected to remain north of Puerto Rico and Hispaniola, although impacts are still likely in those islands. By Thursday, Irma is expected to begin to move over the Lucayan Archipelago as a category 4 hurricane, first passing through the Turks and Caicos Islands and eventually the Bahamas. The track is of moderate confidence through this time. However, by late next week, the setup gets complicated. Models are indicating the possibility that Irma could turn straight north or even northeast while over the Bahamas, missing the United States entirely. There is also a possibility that a ridge of high pressure builds in north of Irma, and Irma makes landfall in the Eastern United States. The 18z Sunday GFS model run predicted that Irma would make landfall in Southeastern North Carolina, while most of its ensemble members were farther south and predicted that Florida would be at the greatest risk. The 12z Sunday ECMWF model run predicted Irma would come very close to Southeastern Florida, before eventually turning northward and remaining offshore the United States Eastern Seaboard. However, more than half of the EPS ensemble members predicted that Irma would make a landfall in the United States. Although a track into the Eastern Gulf of Mexico cannot be ruled out, it is not the likeliest scenario. There is still a large range of possibilities with Irma and it is an extremely complicated situation to predict, and it is best not to focus on a single model run. Model runs are likely to shift, as the possible U.S. impacts are still roughly a week away. We should have a better idea of Irma’s possible impacts to the United States by mid-week.

Elsewhere in the tropics

There are two other tropical disturbances in the Atlantic that could develop into named storms. The first is a tropical wave located over the central Atlantic well southeast of Irma. This tropical wave is currently producing some disorganized showers and thunderstorms, and the NHC gives this wave a near zero percent chance of development within 48 hours and a 60 percent chance within five days. The 12z Sunday CMC, UKMET, and ECMWF model runs predicted that this wave would develop within the next five days into a tropical cyclone as it moves west-northwestward across the tropical Atlantic, although the 18z Sunday GFS predicted no development. It is possible that Hurricane Irma to the west may interfere with development. Another area of disturbed weather is located over the Southeastern Bay of Campeche, and the NHC gives this disturbance a 10 percent chance of development within 48 hours and a 20 percent chance within five days. This disturbance is likely to move very little during the next several days. The 12z Sunday ECMWF, CMC and UKMET model runs predicted this wave would develop into a tropical cyclone, while the GFS model did not show any development. The next two names on the Atlantic naming list are Jose and Katia.

I will be back with another post tomorrow.