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Posted at 01:35 PM ET, 08/30/2010

Hurricane Earl could be close call for East Coast

As of now, storm likely to stay offshore, but not by much

* Our Full Forecast | Katrina lessons | Hurricane Tracking Center *

updated at 2:15 p.m. EDT

Hurricane Earl is a Category 3 storm with maximum sustained winds near 125 mph. Located about 140 miles east-northeast of San Juan, Puerto Rico, Earl is moving west-northwest at 15 mph and is spreading hurricane conditions across the northern Virgin Islands. Hurricane conditions may also threaten Puerto Rico this evening and tonight.

The official intensity forecast calls for Earl to strengthen to 145 mph (Category 4) by tomorrow afternoon. Given that the intensity forecasts for tropical cyclones, though improving, are still less than reliable at times, this expectation should be treated with caution.

Computer model track guidance continues to be moderately clustered around the idea that Earl will indeed recurve out to sea and miss the U.S. coastline, its center bypassing the eastern tip of the Outer Banks of North Carolina by roughly 150 miles at closest approach just after midnight Friday morning.

The ultimate track will be heavily influenced by the timing of an upper-level area of low pressure and associated dip in the jet stream heading eastward from the Northern Plains, and the resulting upper-level winds from the west and northwest over the East Coast. As shown in the forecast map for early Friday (at right), winds from the northwest at high altitudes should be in place across the Carolinas, enough so to deflect Earl back out to sea.

Although the weather models are in reasonably good agreement that the upper-level low will arrive in time to deny a direct hit, typical four-day forecast errors (for both tropical cyclones and upper-level lows) are large enough that residents along the East Coast from Jacksonville, Fla., to Cape Cod, Mass., should pay close attention to the situation.

Keep reading for more on Earl's future and its potential East Coast impacts...

Earl is a moderately large hurricane with sustained hurricane-force winds (74 mph and higher) extending roughly 30-40 miles to the west of its center, and sustained tropical storm-force winds (39 mph and higher) reaching out perhaps 120-140 miles west of center. So even if Earl follows the center line of the official track as currently predicted, tropical storm-force wind gusts and rain squalls could brush the Outer Banks.

Fortunately, the western sides of northward moving tropical cyclones that closely approach the continental U.S. are often dramatically weaker than their eastern sides. These systems, owing to their close proximity to land, often ingest a nontropical offshore flow that tends to weaken the western periphery perhaps more than is often expected.

As Earl moves northward later Friday, the storm is still expected to remain off the Northeast U.S. Coast. Fortunately, cooler ocean waters and strengthening winds aloft should begin to weaken Earl rapidly once it gets north of 40 degrees latitude (roughly the latitude of New York City), though gusty winds and rain squalls may brush Cape Cod.

Rough seas and dangerous rip currents, both from Hurricane Danielle which continues to move away from the U.S. and eventually from Hurricane Earl, are possible all along the Eastern Seaboard for the next several days into the holiday weekend.

By  |  01:35 PM ET, 08/30/2010

Categories:  Tropical Weather

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