Wednesday, September 1, 2010

Hurricane Watch: Big Earl's 'Cone of Uncertainty'

Such a refreshingly honest term compared to NOAA's standard boilerplate:
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From the Wunderblog:
 
And this morning's commentary:
 
...Impact of Earl on North Carolina
The latest set of computer models runs from 2am EDT (6Z) this morning are very similar to the previous set of runs. The NOGAPS model brings Earl closest to the coast, predicting the west eyewall of the the hurricane will hit the Outer Banks of North Carolina near 2am Friday. If this track verifies, a period of 40+ mph winds will affect coastal North Carolina for a period of 12 - 18 hours beginning at about 6pm EDT Thursday night. Earl's expected radius of hurricane-force winds of 60 miles to the west will bring hurricane conditions as far west as Morehead City and Elizabeth City in North Carolina. Earl's radius of tropical storm-force winds to the west, over land, will probably be about 150 miles, so locations from Wilmington to Norfolk could see sustained winds of 40 mph in this worst-case model scenario. Storm surge would not be significant along the North Carolina coast facing the open ocean, since winds would be offshore. However, a significant storm surge of 3 - 6 feet could occur in Pamlico Sound, due to strong west to north winds. Coastal Highway 12 out of the Outer Banks would likely be blocked by sand and debris or washed out, resulting in a multi-day period where everyone on the Outer Banks would be stranded. Is is possible that the NOGAPS scenario is not the worst case, and that Earl will strike farther west, resulting in the Outer Banks getting the fearsome maximum winds of the storm's right front quadrant. However, it is more likely that Earl will pass just offshore, resulting in North Carolina receiving the weaker west side winds. Since Earl's forward speed will be about 20 mph at that time, the winds on the hurricane's west side will be about 20 mph less than the right front quadrant on the east side. The NHC wind probability forecast is calling for a 23% chance of hurricane-force winds on Cape Hatteras, 7% for Morehead City, and 3% for Norfolk, Virginia.

Impact of Earl on New England

The NOGAPS model brings Earl closest to the coast of New England, predicting the west eyewall of the the hurricane will pass over Nantucket at about 2am Saturday morning, and the tip of Cape Cod a few hours later. If this track verifies, 40+ mph winds would affect southeastern Massachusetts for a period of 6 - 12 hours beginning at about 8pm EDT Friday night. Earl should be a weaker Category 1 or 2 hurricane then, with hurricane-force winds extending 30 miles to the left of its track. Hurricane conditions would then affect the eastern tip of Long Island, coastal Rhode Island, and Southeast Massachusetts. Earl's radius of tropical storm-force winds to the north, over land, will probably be about 150 miles, so locations from Central Long Island to southern Boston would experience sustained winds of 40 mph in this worst-case model scenario. A storm surge of 3 - 5 feet might occur in Long Island Sound, and 2 - 3 feet along the south coast of Long Island. A deviation to the left, with a direct hit on eastern Long Island and Providence, Rhode Island, would probably be a $10 billion disaster, as the hurricane would hit a heavily populated area and drive a drive a 5 - 10 foot storm surge up Buzzards Bay and Narragansett Bay. The odds of this occurring are around 5%, according to the latest NHC wind probability forecast. The forecast is calling for a 25% chance of hurricane-force winds on Nantucket, 8% in Providence, 6% in Boston, and 18% in Hyannis. Keep in mind that the average error in position for a 3-day NHC forecast is 185 miles, which is about how far offshore Earl is predicted to be from New England early Saturday morning....MORE