Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Angela Fritz , 9:48 PM GMT on October 25, 2012
Hurricane Sandy is tracking north through the Bahamas this afternoon as a Category 2 hurricane. Maximum wind speeds in the hurricane are 105 mph, with a minimum central pressure of 963 mb. Sandy's center is moving through the eastern Bahamas, about 100 miles southeast of Nassau. The hurricane's eye is still not apparent on satellite nor was it clear in the data from today's Hurricane Hunter mission. Gusts in Nassau have reached 39 mph so far today as the hurricane approaches from the south. Buoys west of Nassau have been recording surface winds up to 39 mph, as well. On Abaco Island, just over an inch of rain has fallen today, and almost an inch of rain has fallen in Miami, where rain started last night.
Sandy's appearance on satellite is a bit ragged this afternoon as it approaches very high wind shear (40-50 knots). The hurricane is obviously already undergoing structural changes this afternoon, caused in part by an upper level low over western Cuba. This low is prohibiting Sandy's outflow on the west side, and as a result, the storm appears asymmetrical with a large area of outflow and circulation to the north, and only a tail of circulation on the southeast of the hurricane. Visually, Sandy is a huge storm. Based on clouds alone, Sandy stretches from Jacksonville, Florida, east to Bermuda, and south to the southern Caribbean Sea. Sandy's radius of outer closed isobar is 350 miles, though tropical storm-force winds only extend around 200 miles from the center.
Figure 1. High resolution MODIS visible satellite imagery of Hurricane Sandy early this morning.
Forecast For Hurricane Sandy
As Sandy moves north, it will grow larger and the hurricane's energy will spread out even more, which will lead to a slight decrease in maximum wind speed. Models agree on this steady decrease in intensity over the next few days, though beyond that, the intensity forecast is still in question since Sandy could begin to gain non-tropical energy as it transitions into a non-tropical storm. The track through Saturday evening remains well understood by the models: Sandy will move north with a slight turn to the west before being yanked north-northeast again by the approaching mid-latitude trough. It's at this point in the forecast that the models diverge, though all but the HWRF are forecasting the unfortunate turn back to the west and into the Northeast U.S. Furthest south along the East Coast is the ECMWF, which forecasts a turn into Maryland/North Carolina on Monday. The GFS forecast is a bit further north than the ECMWF, pushing Sandy onshore near Long Island late Tuesday night. However, this represents a large shift south from earlier GFS runs, and puts the Mid-Atlantic into play more than it was in earlier forecasts. The forecast from the National Hurricane Center appears to be a compromise between the ECMWF and the GFS. The Center is forecasting Sandy to approach the New Jersey coast on Tuesday afternoon.
There are many questions surrounding this hurricane and its forecast, but I find it important to convey that Sandy's impacts will be widespread, no matter the location of "landfall." Risk to the Mid-Atlantic seems higher this afternoon, and as Jeff noted in his morning blog, Sandy will be a very large and possibly non-tropical storm as it approaches the coast, with gale-force winds extending up to 300 miles from its center. This increases the probability of storm surge extending far from the center of the storm, which, combined with the timing of a full moon tide, is a big concern, along with freshwater and river flooding from heavy, extended periods of rain.
Figure 2. Today's "extra" 18Z (2pm EDT) weather balloon launched from the Peachtree City office of the National Weather Service. The National Weather Service is launching extra weather balloons all over the country to improve the quality of forecasts as Sandy approaches. Thanks to NWS Meteorologist Alex Gibbs for snapping this shot just before launch!
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