Hurricane Irma strengthened into a category 4 hurricane Monday afternoon east of the Leeward Islands, and is likely to strengthen slightly more as it approaches the Islands early Wednesday morning. It is a distinct possibility that Irma could strengthen into a category 5 hurricane. Hurricane Warnings are currently in effect for the Leeward Islands as well as Puerto Rico, and Irma is likely to take a west-northwestward path towards the Bahamas and eventually South Florida by this weekend. There is an increasing chance that Irma directly affects the United States, with South Florida the most at risk.

As of 11:00 p.m. EDT, Hurricane Irma was centered near 16.7°N 55.6°W, and was moving westward at about 13 mph. Maximum sustained winds were 120 knots (140 mph), with an estimated minimum pressure of 943 mb. The 120-knot intensity could be a little conservative, based on an estimated surface wind of 126 knots just recorded by a reconnaissance aircraft. Irma is currently located in a favorable environment for intensification, with sea surface temperatures a warm 29°C (84.2°F), wind shear a light 5-10 knots, and increasing mid-level moisture. Irma just recently completed an eyewall replacement cycle and a large eye is beginning to clear out this evening surrounded by a ring of deep convection. Additional intensification seems likely, and Irma is likely to be just under category 5 strength by the time it approaches the Leeward Islands early Wednesday morning.

Irma is expected to pass just north of Puerto Rico on Wednesday evening, and pass just north of Hispaniola on Thursday evening while it begins to move over the Turks and Caicos Islands. By Friday, Irma is expected to move over the Southern Bahamas. After that time, the forecast becomes uncertain. The official National Hurricane Center (NHC) forecast predicts that Irma will emerge into the Straits of Florida on Saturday. On Saturday or Sunday, Irma is likely to make a turn to the north, but it is unclear where and when the turn will occur. It is possible that Irma could turn to the north before making a direct landfall in Florida, and that would put the United States East Coast the most at risk. Another possibility is Irma turns directly northward right over the Florida Peninsula and eventually weakens inland. A third possibility is that Irma emerges into the extreme eastern Gulf of Mexico and eventually strikes western Florida. It appears less likely today that Irma will curve out to sea without United States impacts, although this scenario still cannot be ruled out. The official NHC forecast predicts that Irma will weaken by late week as it moves closer to Cuba and the Florida Coast. While a direct landfall is not expected, residents of Cuba and Hispaniola should continue to monitor the progress of Irma.

Preparations should be rushed to completion for residents of the Leeward Islands, the Virgin Islands, and Puerto Rico. A Hurricane Warning is currently in effect for the following areas: Antigua, Barbuda, Anguilla, Montserrat, St. Kitts, Nevis, Saba, St. Eustatius, and Sint Maarten, Saint Martin, Saint Barthelemy, the British Virgin Islands, the U.S. Virgin Islands, Puerto Rico, Vieques, and Culebra. A Hurricane Watch and Tropical Storm Warning is in effect for Guadeloupe. A Tropical Storm Watch is in effect for Dominica. Residents of the Turks and Caicos Islands, The Bahamas, and even South Florida, should begin to prepare for Irma, as direct impacts appear likely. Right now, it appears that Florida is at greatest risk of direct impacts from Irma, but Georgia, the Carolinas, and even the Mid-Atlantic States should continue to closely monitor the progress of Irma if it turns to the north sooner than anticipated.

I will be back tomorrow with another post on Irma, as well as Invests 94L and 95L which could both develop into tropical cyclones this week over the Atlantic.