Hurricane Irene update @5:15 pm EDT
Irene strengthens to a major hurricane
Originally posted at 2115 UTC Aug 24 - last edited August 31 (no content changes)
As stated yesterday while commenting on the main blog, the biggest threat for Hispanola was after Irene's center lifted north of the Windward Passage (area of ocean between Cuba, Haiti and Jamaica). Today, that famous "SW dry slot" that was weakening Irene is now over water, pushing convection into much of Haiti and the Dominican Republic. A persistent burst of convection has thus formed over central southern Dominican Republic (despite being an incredibly dry storm north of the Dominican), creating the risk for flash floods over that area and south toward the capital, Santo Domingo.
Waves offshore Santo Domingo, after the passage of Irene. Courtesy Erika Santelices. Read more here: Hurricane Irene to bring significant rainfall to Quebec
Topography of Hispanola.
The main threat area is now, of course, the Bahamas. Irene's eye wobbled over the Turks and Caicos Islands, before turning northwest last night. The NHC track places much of the Atlantic-side Bahamas under the main forecast track, yet this means that other places including Nassau, Freeport and Eleuthra will see storm surge arrive from the southeast, switch briefly to the east and then come in from the north.
AMSRE "radar from space" rainfall for Irene at 1813 UTC.
Irene is now expanding in size. Remember that in any hurricane, major threats such as storm surge and rip currents can arrive hours, even days before a storm makes landfall, and even areas not expecting a landfall need to take precautions. We saw this in Hurricane Ike, which brought surge conditions and overtopping waves taller than humans 24 hours before the storm made landfall.
Even after a storm passes, hazards include persistant flooding, as we are seeing now in Hispanola. Landfalling storms can induce inland flooding for 24, 48, even 72 hours.
Never go outside during the eye of the storm. Even when the sky is clear, storm surge is still at its highest, and hazards such as downed power lines will be present.
Unlike Hurricane Frances, which paralleled the Bahamas to its northeast before hitting Florida as a category two storm, Irene is not expected to weaken prior to exiting the Bahamas. Nor, in fact, is it expected to hit Florida. It is always a risk for a storm to veer off track, yet an upper-level low (with convection) has been almost stalled over the Gulf Stream, south of the Carolinas for the past 24 hours, at the end of a TUTT-like frontal boundary.
This, along with a cold front expected to develop tonight from a low centered over Lake Superior, will most likely act to pull Irene toward the south-of-Carolinas low as it tracks into the northernmost Bahamas. Considering the warmth of the Gulf Stream, further strengthening is likely, yet possible weakening factors include the dry air over the Gulf-Texas-Southeast region, and interaction with the TUTT.
Track of Hurricane Frances, 2004.
After encountering a cold front, Irene will likely get pulled rapidly northward. Following the storm's passage into cooler waters immediately south of Long Island, Irene may begin a rapid transition into extratropical status. This, however, will mean inland flooding northeast of the Allegheny Mountains, including northern New England, New Brunswick, and potentially the Lake Champlain-Richelieu Valley region, which was hit by flooding earlier this year.
There will likely be complex interactions between Irene, the Gulf stream, warmer eddies in the Gulf Stream (the warmest of which at SST of 31C+), the Labrador Current (the cold ocean current, section extending from Grand Banks of Newfoundland, off the coast of Nova Scotia, down toward Long Island, the Chesapeake Bay entrance and to Cape Hatteras), the dry air mass over the United States, the TUTT, thunderstorms over the United States, upper-level lows, cold fronts, and potentially even other Invests. One thing to keep in mind: the general track of Irene will be roughly along the Gulf Stream, where evaporation will fuel the storm in barometric/windspeed intensity as well as in rainfall.
Current water vapor imagery of Western North Atlantic Region. This image refreshes itself. Notice the continuing convection (Hispanola, Puerto Rico, Jamaica, and even extending to South America and the Lesser Antilles), stream of moisture extending NE from the Yucatan across Florida and the south-of-Carolinas low toward Bermuda and into the open Atlantic, and the area of dry air digging south from Virginia to the NE Gulf which will hit Irene after the first cold front.
NHC 5 pm
As of 5 pm August 24, Irene was a category 3 hurricane, predicted to track into Cape Hatteras as a major hurricane, into Long Island as a hurricane and into Maine as an extratropical storm.