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October 2012

Sandy Weaker in the NW Bahamas, Expected to Become Dangerous for NE US

   Posted by Levi at 3:40pm on October 26, 2012

Hurricane Sandy is now moving through the NW Bahamas, and has weakened since yesterday. The center is now exposed due to southwesterly wind shear imposed by the subtropical jet. This weakening was expected, but has occurred a bit sooner than anticipated. This is good news for the northern Bahamas and eastern Florida, which are not receiving as big of a lashing as they would have. Despite having an exposed center, Sandy remains a solid hurricane, and her central pressure is still below 980mb. As Sandy’s center passes through the subtropical jet core, some additional weakening may occur, but she will likely remain a hurricane. As Sandy begins to accelerate northeastward in 24 hours or so, upper winds over the storm will lighten a bit, and upper-level dynamics will continue to improve, with significant divergence in the 200mb wind field expected to develop in the path of the storm to the north and northwest. Thus, some restrengthening is expected in the maximum winds. The increase in wind will likely remain limited due to the ever-expanding nature of Sandy’s wind field, but her central pressure is expected to drop significantly due to baroclinic dynamics as she nears the Atlantic coast. As a result, an area of tropical storm force winds several hundred miles in diameter will affect the northeastern U.S., and hurricane force winds will likely affect the coastline where the storm moves ashore.

The track forecast philosophy for Sandy remains unchanged. An acceleration to the NE or NNE as the ridge to the north moves out of the way will occur during the next day or two, bringing Sandy up between Cape Hatteras and Bermuda. The storm’s structure has become weighted to the north and northwest as expected, and this will allow the storm to interact positively with a mid-latitude trough moving into the eastern United States. The resulting phasing will draw the storm towards the north and northwest, with a sharp left turn likely before an eventual landfall on the mid-Atlantic or New England coast. The forecast track has been shifted a bit southward Days 4-5, and remains in good agreement with the consistent ECMWF ensemble mean, but lies still north and east of the ECMWF operational.

Sandy has the potential to become a historic storm for the northeast U.S., and residents should be prepared for hurricane conditions along the coastline and tropical storm conditions well inland and well away from where the center of circulation comes ashore. Due to baroclinic enhancement, Sandy’s circulation continues to expand, and tropical storm force winds will extend over 300 miles from the center at landfall. Prolonged heavy rain and storm surge are likely to cause severe damage in some areas, and residents are urged to treat this as another Irene-type event.

We shall see what happens!