Total ocean heat content (OHC) along the track of Hurricane Irma, at 2 am EDT Monday, 4 September 2017. Irma is expected to encounter OHC levels of 80 – 100 kilojoules per square centimeter as it passes the Lesser Antilles islands. OHC levels this high are known to be very favorable for rapid intensification, and are similar to what fueled Hurricane Harvey’s rapid intensification over the Gulf of Mexico during its approach to the Texas coast. Graphic: University of Miami Rosenstiel School of Marine and Atmospheric Science

By Bob Henson 
4 September 2017

(Weather Underground) – Dangerous Hurricane Irma was intensifying as it approached the northern Lesser Antilles Islands on Monday morning, and island residents in the path of Irma need to rush preparations to completion as the storm heads west-southwest at 14 mph. A NOAA hurricane hunter aircraft in the storm found that Irma’s central pressure was steadily dropping Monday morning, reaching 944 mb at 11 am EDT. Irma's top sustained winds are estimated at 120 mph, and winds may not yet have fully responded to this pressure drop. Irma is very likely to be a major Category 3 or 4 hurricane when it passes very close to the northern Lesser Antilles Islands on Tuesday, near Puerto Rico and the Virgin Islands on Wednesday, and the Turks and Caicos Islands and Hispaniola on Thursday. Hurricane Warnings are now in effect for the northern Leeward Islands, and Hurricane Watches are up for the U.S. and British Virgin Islands and Puerto Rico.

Tropical storm-force winds are expected to begin affecting the east coast of Florida and the Florida Keys on Friday night. An evacuation decision for the Florida Keys may have to come as early as Tuesday, since the Keys require 3+ days to evacuate.

Satellite images on Monday morning showed a very symmetric well-organized storm with solid spiral banding and a large eye. Irma had a respectable and improving upper-level outflow on all sides. Conditions were favorable for strengthening, with wind shear a low 5 – 10 knots. Sea surface temperatures (SSTs) along Irma's path have risen sharply over the past day, to 29°C (84°F), accompanied by a substantial increase in the total heat content of the ocean, giving the storm plenty of heat energy to fuel intensification. The surrounding atmosphere has been steadily moistening, as seen on precipitable water imagery, with a mid-level relative humidity near 55%, according to the 12Z Monday analysis from the SHIPS model. [more]

Threat Increasing for Cuba, Florida from Intensifying Irma

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