by Jeff Masters, Wunderblog, September 2, 2010
Hurricane Earl strengthened significantly overnight, and its Category 4, 140-mph winds make it the third strongest Atlantic hurricane on record so far north in U.S. coastal waters. Only Hurricane Esther of 1961 and Hurricane Connie of 1955 made it farther north in U.S. coastal waters at a higher strength. Both storms had winds 5 mph stronger than Earl -- 145 mph. One other Atlantic hurricane was stronger than Esther and Connie at a more northerly latitude--the second storm of 1922, which had winds of 150 mph. However, this hurricane was far out at sea, north of Bermuda.
Earl has made its turn to the north, and is headed for a close brush with North Carolina's Outer Banks. Rain bands from the hurricane are now visible on long-range Cape Hatteras radar, and these rain bands will begin to spread over coastal North Carolina this afternoon. Recent satellite imagery shows an extremely impressive major hurricane, that will be resistant to sudden changes in intensity.
Figure 1. MODIS image of Earl taken at 2pm EDT September 1, 2010, by NASA's Aqua satellite. Image credit: NASA.
Forecast for Earl
The latest set of model runs from 2am EDT (6Z) this morning show little change to Earl's track. The latest SHIPS model forecastshows wind shear will remain moderate, 10-15 knots, through Friday morning. This should allow Earl to maintain major hurricane status as it passes North Carolina early Friday morning. By Friday night, as Earl gets caught in the jet stream and accelerates to the northeast, wind shear will rise to 20-30 knots and ocean temperatures will plunge to 20 °C, resulting in considerable weakening. Earl will still probably be a Category 2 hurricane early Saturday morning, when it will make its closest approach to New England. Earl is more likely to be a Category 1 hurricane early Saturday afternoon, when it is expected to make landfall in Nova Scotia, Canada.
Figure 2. Wind field analysis of Hurricane Earl from 9:30am EDT Thursday, September 2, 2010. Note the asymmetry in Earl's wind field, caused by the storm's forward motion of 18 mph to the north-northwest at the time. The highest contour has top winds of 110 kt (130 mph) surrounding the "X" on the NNE side of Earl -- the strong right front quadrant of the storm. However, winds in the left front quadrant (on the SSW side) were just 80-85 knots (92-97 mph.) Image credit: NOAA/AOML/Hurricane Research Division.
Earl is a large hurricane, which gives it a higher potential for storm surge damage than a smaller hurricane with the same top winds. One measure of a storm's power, useful for gauging storm surge threat, is to measure the speed of the winds and multiply by the area over which those winds blow. This total is called the Integrated Kinetic Energy (IKE). Based on the storm's IKE, one can come up with a scale from 0-6 rating the storm's destructive power from its storm surge. A separate rating can be given to the destructive potential of the storm's winds. The IKE value of 99 Terrajoules for Earl, at 9:30 a.m. EDT today, gives its storm surge a destructive power of 4.9 on a scale of 0-6. Earl's winds have a similar destructive power, 4.9 on a scale of 0-6. Let's hope the right front quadrant of Earl, where the main storm surge would occur, stays offshore! For comparison, the small Category 5 Hurricane Camille of 1969 had an IKE of 80 Terrajoules, and the very large Category 2 Hurricane Ike of 2008 had an IKE of 116 Terrajoules, higher than Category 4 Earl's.
Impact of Earl on North Carolina
Earl's eye is expected to stay offshore of North Carolina. However, much of coastal North Carolina will experience tropical storm-force winds of 39+ mph for a period of 12-18 hours beginning this afternoon or early this evening. Earl's expected radius of hurricane-force winds of 90 miles to the west may bring hurricane conditions to the Outer Banks, but probably not to mainland 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. Storm surge will likely be less than two feet along the North Carolina coast west of Cape Hatteras facing the open ocean, since winds will be offshore. However, a significant storm surge of 3-5 feet can be expected on the south side of Pamlico Sound, due to strong northerly winds. A 3-5 foot storm surge is also likely along the Outer Banks from Cape Hatteras northward 50 miles to Nags Head. NHC is giving a 10% chance that the storm surge will reach 7-9 feet along the coast near Nags Head. It is possible that Coastal Highway 12 out of the Outer Banks will be blocked by sand and debris, or washed out, resulting in a multi-day period where everyone on the Outer Banks will be stranded. Since Earl's forward speed will be about 20 mph as it passes Cape Hatteras, the winds on the hurricane's west side will be about 40 mph less than on the east side (Figure 2). (I regret that I misstated this yesterday. To think about this, imagine a stationary hurricane with 120 mph winds on all sides. Now, put the hurricane in motion. The winds are still 120 mph on all sides, relative to a frame of reference that moves with the storm, but an observer on the ground will see 140-mph winds in the right front quadrant, and 100 mph on the left side.) The NHC wind probability forecast is calling for a 13% chance of hurricane-force winds on Cape Hatteras, 1% for Morehead City, and no chance for Norfolk, Virginia.
Figure 3. NHC is giving a 10% chance that the storm surge will reach heights of 7-9 feet along the Outer Banks of North Carolina near Nags Head. Image credit: National Hurricane Center.
Impact of Earl on New England
Residents in Eastern Long Island, Rhode Island, and Southeast Massachusetts need to complete all of their hurricane preparations by early Friday morning. By Friday afternoon, winds will rise quickly. Earl's recent increase in strength means that New England will see a stronger hurricane than was expected. The latest track forecasts still keep the eye barely offshore, or have it passing over Nantucket and the extreme eastern tip of Cape Cod, Massachusetts. The 5 a.m. NHC intensity forecast calls for Earl to have top winds of 100 mph at 2am Saturday, when the storm is expected to be over or just offshore of the eastern tip of Cape Cod. Earl will be moving near 25 mph at that time, meaning that that top sustained winds on the north side of the eye, over land, will be 50 mph, and the winds will be 100 mph on the south side over water. NHC is giving a 10% chance that a storm surge of 3-5 feet will occur in Long Island Sound (Figure 4) and 2-3 feet along the south coast of Long Island. A small deviation in Earl's track to the left, resulting in 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 7-15 foot storm surge up Buzzards Bay and Narragansett Bay. The odds of this occurring are around 3%, according to the latest NHC wind probability forecast. The forecast is calling for a 28% chance of hurricane-force winds on Nantucket, 7% in Providence, 4% in Boston, 7% in Eastport, Maine, and 17% in Hyannis.
Figure 4. NHC is giving a 10% chance that the storm surge will reach heights of 3-5 feet from Long Island Sound to Southeast Massachusetts. Image credit: National Hurricane Center.
Impact of Earl on Canada
Winds will begin to rise on the southwest coast of Nova Scotia early Saturday morning, and all preparations need to be completed by Friday night. By late morning Saturday, Earl is expected to make landfall somewhere between the Maine/New Brunswick border and central Nova Scotia. At that time, Earl will probably be a Category 1 hurricane. Earl will be moving at a very rapid 25-30 mph when it arrives in Canada, and regions on the right side of the eye can expect winds 50-60 mph greater than on the left side, due to the fast forward motion of the hurricane. It is unlikely that Earl will be as damaging as Hurricane Juan, the 2003 Category 2 hurricane which made a direct hit on Halifax, Nova Scotia, causing over $200 million in damage. Earl's impact is likely to be greater than 2008's Hurricane Kyle, the last hurricane to hit Nova Scotia. Kyle hit near Yarmouth, Nova Scotia, as a Category 1 hurricane with 75-mph winds. Kyle produced a storm surge of 2.6 feet and did $9 million in damage to Canada. The NHC wind probability forecast is calling for a 14% chance of hurricane-force winds in Yarmouth, and 4% in Halifax.
Beach erosion
Regardless of Earl's exact track, the U.S. East Coast can expect a long period of high waves today and Friday. Significant beach erosion and dangerous rip currents will be the rule, due to waves that will reach 10-15 feet in offshore waters. Waves are expected to reach 25-30 feet along the Cape Hatteras, North Carolina, shore tonight. Beach erosion damage in the mid-Atlantic states will likely run into the millions, but will probably not be as bad as that suffered during Nor'easter Ida in November of 2009. That storm (the remains of Hurricane Ida that developed into a Nor'easter) remained off the coast for several days, resulting in a long-duration pounding of the shore that caused $300 million in damage -- $180 million in New Jersey alone.
Link: http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=1601
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