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October 2012

Sandy Blasting Jamaica as a Hurricane, will be a Big Problem from Bahamas to Canada

   Posted by Levi at 4:43pm on October 24, 2012

Sandy has now strengthened rapidly into a hurricane, acquiring heavy wrapped banding that has allowed an eyewall to form, causing a tightening of the wind field. Sandy will make landfall on the eastern end of Jamaica later today, and then quickly move over eastern Cuba. This should slow down Sandy’s strengthening, but should only be a speedbump, and Sandy will likely continue strengthening over the Bahamas. The environment is fairly conducive for strengthening, with a strong divergent flow aloft that will be enhanced by a digging upper trough over the eastern Gulf of Mexico over the next 3 days, and a healthy pressure gradient to the north of the storm that is aiding the rising motion of the air in the Caribbean right now. Dry air will eventually wrap into Sandy from the west and south, but if she continues to deepen, she should be able to maintain some sort of a central core while in the Bahamas. Her NW quadrant is likely to become the strongest part of the storm, and thus the northern Bahamas will likely receive the worst conditions, and the eastern part of Florida will likely see tropical storm conditions.

The long-term track of Sandy remains a bit uncertain, as her potential interactions with New England are still about 6 days away, but my forecast track continues to call for a NW turn into the mid-latitude trough that will be digging strongly into the northeast U.S. during that time. The GFS through the 06z run, which was used when I recorded the video above, still let Sandy escape out to sea, along with the CMC model. However, the 12z GFS has now come around to the idea that Sandy should phase with the trough to the west and curve back into New England. With this new shift from the GFS, the confidence in the forecast track below is reinforced even more. Sandy will be deepening constantly as she phases with the mid-latitude trough, but her wind field will be expanding as she loses tropical characteristics, and thus her maximum wind speed may remain roughly constant as she moves northward. It is hard to say exactly how strong the winds of this hybrid system will be once it nears New England. It will depend on how strong Sandy gets and what her hybrid structure is like. Regardless, this would be one of the strongest autumn storms to ever hit the northeast U.S., and the impacts would be severe. The forecast track lies east of the ECMWF operational and more in line with the ECMWF ensemble mean, given that the ECMWF is likely overdeepening the system and moving it a bit too far west. With 6 days or so to go before New England potentially the wrath of Sandy, there is still plenty of opportunity for the forecast to change, but if the 12z GFS is the start of the models agreeing on this general track forecast, then New England should expect that this will indeed go down as the great Halloween storm of 2012.

We shall see what happens!