Earl spares North Carolina, heads for New England

Hurricane Earl sideswiped North Carolina's Outer Banks early this morning, passing just 75 miles east of Cape Hatteras. Special weather statements indicate that the only road out of the barrier island chain, Highway 12, is closed. Pounding waves over 15 feet high, on top of a storm surge of 2 - 3 feet, pushed water over the highway in multiple locations. Earl's winds also piled up huge waves offshore--waves peaked at 28 feet at the Diamond Shoals buoy, and at 31 feet at a buoy 150 nm offshore of Cape Hatteras. Peak wind gusts from Earl were 74 mph at 12:30am at Oregon Inlet, and 70 mph at Nags Head and Manteo. Sustained winds of 47 mph were recorded at Oregon Inlet, but sustained winds at Cape Hatteras never reached tropical storm force--top winds there were just 36 mph, with gusts to 62 mph. Radar estimated rainfall (Figure 2) for Earl from the Cape Hatteras, North Carolina radar shows that 3 - 4 inches of rain fell across much of the Outer Banks. Overall, aside from some significant beach erosion, Earl spared North Carolina.


Figure 1. MODIS image of Earl taken at 11:29am EDT September 2, 2010, by NASA's Terra satellite. At the time, Earl was a Category 3 hurricane with top winds of 125 mph. The storm had a somewhat lopsided shape, due to wind shear from the southwest affecting the storm. Image credit: NASA.

Earl is now headed to the north-northeast at 18 mph. Conditions will steadily improve today over North Carolina, but deteriorate over New England. Earl's outer rain bands have now reached New York's Long Island, as seen on long range Dover radar. Satellite imagery shows that Earl is no longer the impressive hurricane it once was. The eye is no longer visible, and the hurricane appears lopsided, due upper level winds out of the southwest that are creating a moderate 10 - 20 knots of wind shear. The latest 10:02am EDT eye report from the Hurricane Hunters showed that Earl continues to weaken, with a central pressure up to 961 mb. Top surface winds measured via their SFMR instrument were just 76 mph--barely Category 1 strength.


Figure 2. Radar estimated rainfall for Earl from the Cape Hatteras, North Carolina radar shows that 3 - 4 inches of rain fell across much of the Outer Banks.

Forecast for Earl
The latest set of model runs from 2am EDT (6Z) this morning show little change to Earl's track. Earl is expected to pass 20 - 50 miles southeast of Nantucket and Cape Cod, Massachusetts, at about 2am Saturday. The latest SHIPS model forecast of wind shear also shows no surprises. Wind shear will remain moderate, 10 - 20 knots today, then increase to the high range, 20 - 30 knots, on Saturday. Ocean temperatures will plunge to 20°C early Saturday morning, resulting in considerable weakening. Earl will still probably be a weak Category 1 hurricane early Saturday morning, when it will make its closest approach to New England. Earl is more likely to be a strong tropical storm early Saturday afternoon, when it is expected to make landfall in Nova Scotia or New Brunswick, Canada.


Figure 3. Wind field analysis of Hurricane Earl from 9:30am EDT Friday, September 3, 2010. Note the 15 mph asymmetry in Earl's wind field, caused by the storm's forward motion of 18 mph to the north-northeast at the time. The highest contour had top winds of 75 kt (87 mph) surrounding the "+" on the east side of Earl--the strong right front quadrant of the storm. However, winds on the left (west) side were just 65 knots (74 mph.) The asymmetry was greater--about 20 mph--at 6:30 am EDT this morning. Image credit: NOAA/AOML/Hurricane Research Division.

Impact of Earl on New England
The latest track forecasts still keep Earl's eye barely offshore of New England, with the center passing 20 - 60 miles southeast of Nantucket and the extreme eastern tip of Cape Cod, Massachusetts. The 11am NHC intensity forecast calls for Earl to have top winds of 75 mph at 2am Saturday, when the storm is expected to be at its closest to Massachusetts. Earl will be moving northeastward near 25 mph at that time, meaning that we will see a large difference in the winds between the weak and strong sides of this fast-moving hurricane. This difference is likely to be about 15 - 20 mph, based on the wind distribution around Earl's eye seen so far this morning. Winds analyzed on the experimental H*Wind product put out by NOAA's Hurricane Research Division at 9:30am this morning (Figure 3) showed that the winds on the weak left side of the storm were about 15 mph less than the winds in the powerful right front quadrant. Assuming Earl maintains this structure for the next day, we can expect the hurricane will have top winds of 75 mph on its strong southeast side over water when it whips by Southeast Massachusetts early Saturday morning, and winds of 55 - 60 mph in its northwest eyewall, closest to Massachusetts. If Cape Cod and Nantucket barely miss Earl's northwest eyewall, as currently forecast, top winds in those locations might only reach 45 - 50 mph. The latest NHC wind probability forecast from 11am this morning gives Nantucket a 12% chance of receiving sustained hurricane force winds of 74+ mph, and Hyannis on Cape Cod a 3% chance.

The highest storm surge from Earl is likely to be on the south side of Cape Cod Bay, due to the northeast winds that will be piling up water in the bay. NHC is giving a 10% chance that a storm surge of 3 - 5 feet will occur in Cape Cod Bay, but it is more likely that the surge will be 2 - 3 feet. The extreme western portion of Long Island Sound at New York City could see a storm surge bringing water levels 1 - 2 feet above ground level.


Figure 4. NHC is giving a 10% chance that the storm surge will reach heights of 3 - 5 feet in southern Cape Cod Bay. Image credit: National Hurricane Center.

Impact of Earl on Canada
Winds will begin to rise on the southwest coast of Nova Scotia late Friday night and early Saturday morning. 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 strong tropical storm with 55 - 60 mph winds. 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 15 - 20 mph greater than on the left side, due to the fast forward motion of the hurricane. Earl's impact is likely to be less 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 11am EDT NHC wind probability forecast is calling for a 15% chance of hurricane-force winds in Yarmouth, and 3% in Halifax.

Fiona
There is not much to Tropical Storm Fiona, which satellite loops show to be a naked swirl of low clouds with just one diminishing spot of heavy thunderstorms on the southwest side of the circulation. High wind shear from Earl should continue to affect Fiona over the next two days, and be able to destroy the storm by Saturday.


Figure 5. Morning satellite image of Gaston's remains (left) and the latest tropical wave to move off of Africa (right).

Gaston may regenerate
Tropical storm Gaston lost its battle with dry air yesterday, degenerating into a disorganized low pressure area. Recent satellite imagery shows that Gaston's remains have developed a broad surface circulation again, and a few heavy thunderstorms have begun to appear. The latest SHIPS model forecast predicts shear will remain low to moderate, 5 - 15 knots, for the next five days, so it is possible Gaston could regenerate. The large amount of dry air surrounding Gaston's remains seen on water vapor satellite loops will continue to be a major impediment to development. NHC is giving Gaston a 40% chance of regenerating into a tropical depression by Sunday. I'd put these odds a little higher, at 60%. The GFS model develops Gaston and predicts it will move though the Lesser Antilles on Wednesday. The NOGAPS and Canadian models also indicate Gaston will re-develop, but move the storm slower and show it near the northern Lesser Antilles seven days from now.

New tropical wave
A large tropical off the coast of Africa is moving westward at about 10 mph, and has the potential to develop into a tropical depression next week. NHC is giving the wave a 10% chance of developing by Sunday afternoon. Wind shear is currently too high, 20 - 30 knots, for the wave to develop. However, once the wave reaches a point a few hundred miles from the Cape Verdes Islands two days from now, wind shear will drop and development will be more likely.

Next post
I'll have an update late this afternoon.

Jeff Masters