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Earl poised to rapidly intensify ; now pounding northern Lesser Antilles

By: Dr. Jeff Masters, 1:16 AM GMT on August 30, 2010

It's time to make final preparations and get ready to ride out the storm if you live in the northern Lesser Antilles Islands tonight, as Hurricane Earl is on your doorstep. Earl continues to intensify steadily, though not explosively. An Air Force Hurricane Hunter aircraft found a central pressure of 972 mb at 7:38 pm EDT. This is a significant drop of 13 mb in ten hours. As is usually the case, it takes six or so hours for a hurricane's winds to respond to a major pressure change, and Earl's winds are now beginning to ramp up. Top flight level winds at 10,000 feet seen by the Air Force were 106 mph. Using the usual rule of thumb that the surface winds are 90% of the 10,000 foot flight level winds gives one surface winds of 97 mph, which is right at the border of Cat 1/ Cat 2 strength. Top winds seen at the surface by the Air Force's SFMR instrument were lower, 78 mph, but a NOAA research P-3 in the storm recently saw surface winds of 88 mph. I expect that the Air Force will be measuring Cat 2 surface winds before their mission is over tonight. Martinique radar shows that Earl has a large, 35 mile wide eye. Earl initially formed a smaller eye, but this collapsed almost immediately, and the larger diameter eyewall took over--kind of an instant eyewall replacement cycle right as the eye initially formed, something I don't recall ever seeing before. The latest eye report from 7:38 pm EDT showed that the temperature difference from outside the eye to inside the eye had increased from 3°C to 8°C in just 1 1/2 hours. This is a huge spike in temperature, and indicates that Earl may be on the verge of a period of more rapid deepening, which will likely carry it to Category 3 or 4 strength by Monday night. Recent satellite imagery shows the storm is lopsided, with much more intense thunderstorm activity on the southern side. This is due to 10 knots of wind shear from strong northerly upper level winds, courtesy of the outflow from Hurricane Danielle. This shear has steadily decreased today, and will continue to decrease tonight and Monday.

Figure 1. Radar image of Earl taken at 8:45 pm AST. Image credit: Meteo France.

Track forecast for Earl
Latest radar animations out of Martinique and St. Maarten show that the eye of Earl is on track to pass just to the northeast of the islands of Barbuda, St. Barthelemy, Anguilla, and St. Maartin in the northernmost Lesser Antilles Islands tonight and Monday morning. Since the eye is so wide, it appears that portions of the southern eyewall will pass over these islands. The southern eyewall is where the NOAA aircraft just measured 88 mph winds, so Barbuda could well see sustained winds of 90 mph for a period of up to two hours, since the storm is moving near 14 mph and has a 35-mile wide eye. Since Earl will probably start intensifying rapidly in the next few hours, Anguilla, the last island in the path of Earl's southern eyewall, could see sustained winds near 95 - 105 mph between 7am - 9am AST. These are worst-case scenarios, and hopefully Earl's southern eyewall will barely miss these islands, bringing winds just below hurricane force.

The latest set of model runs (18Z, 2pm EDT) show Earl shooting the gap between Bermuda and the U.S. East Coast over the next five days, and none of the models take Earl ashore over the U.S. North Carolina is now outside the cone of uncertainty. Recall that the average error in a 5-day track forecast is about 300 miles, so it is still too early to be confident Earl will miss the U.S. The most likely landfall location, were Earl to hit the U.S., would be Cape Cod, Massachusetts. A more likely landfall location appears to be Nova Scotia or Newfoundland, but it is too early to say which province is most at risk.

Hurricane History for the northern Lesser Antilles
The last hurricane to pass through the northern Lesser Antilles Islands was Category 4 Hurricane Omar, on October 16, 2008. Omar's eyewall missed all of the islands, but the storm did $80 million in damage to the Caribbean, mainly on the islands of Antigua, Barbuda, Dominica, the SSS Islands (Saba, St. Eustatius, and St. Maarten), and the U.S. Virgin Islands. No direct deaths were attributed to Omar, and the name Omar was not retired from the 6-year rotating list of hurricane names.

Links to track Earl
Martinique radar
St. Maarten radar
Wundermap of the northern Lesser Antilles Islands
St. Maarten weather history for August 29
Long range radar out of San Juan, Puerto Rico (now back up!)
Visible rapid scan satellite loop

I'll have a full update in the morning.

Jeff Masters


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.