Earl's rain bands move over New England; Gaston regenerating?

Hurricane Earl has remained roughly constant in intensity over the past six hours, as it heads north-northeast at 20 mph towards New England. The latest center fix from the Hurricane Hunters, at 1:14pm EDT, found the pressure had remained constant since late morning, at 961 mb. Long range radar out of Long Island shows that Earl's outermost spiral bands have already brought as much as one inch of rain to portions of Massachusetts and Rhode Island, with lesser amounts on Long Island and in Connecticut.


Figure 1. Afternoon radar image from the Long Island, New York radar.

Forecast for Earl
The latest set of model runs from 8am EDT (12Z) this morning show little change to Earl's track. Earl is still 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 continues to show that shear will 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 probably be a strong tropical storm with 70 mph winds early Saturday morning, when it will make its closest approach to New England, and have 65 mph winds on Saturday afternoon, when it is expected to make landfall in Nova Scotia or New Brunswick, Canada. I have no substantive changes to make to the impacts likely for New England and Canada that I discussed in this morning's post.


Figure 2. Wind field analysis of Hurricane Earl from 3:30pm EDT Friday, September 3, 2010. Note the 15 mph (13 kt) asymmetry in Earl's wind field, caused by the storm's forward motion of 20 mph to the north-northeast at the time. The highest contour had top winds of 65 kt (75 mph) surrounding the "+" on the east side of Earl--the strong right front quadrant of the storm. However, winds on the left (northwest) side were just 52 knots (60 mph.) The asymmetry was greater--about 20 mph--at 6:30 am EDT this morning. Image credit: NOAA/AOML/Hurricane Research Division.

Fiona
Tropical Storm Fiona has changed little this afternoon. Satellite loops continue to show that Fiona is 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 will probably destroy the storm on Saturday.


Figure 3. Afternoon satellite image of Gaston's remains.

Gaston may be regenerating
Recent satellite imagery continues to show that Gaston's remains are re-organizing. Gaston has a broad surface circulation, but not enough heavy thunderstorm activity to be considered a tropical depression. A large amount of dry air lies to the west and north of Gaston's remains, as seen on water vapor satellite loops. This dry air will continue to be a major impediment to development. The latest SHIPS model forecast predicts shear will remain moderate, 10 - 15 knots, for the next five days. The winds creating the shear are coming from the east, where the atmosphere is relatively moist, so this shear will be less harmful than usual for development. NHC is giving Gaston a 50% chance of regenerating into a tropical depression by Sunday; I put these odds higher, at 60%. The GFS, UKMET, and GFDL models develop Gaston and predict it will move though the Lesser Antilles on Wednesday. The NOGAPS and HWRF models also develop Gaston, but predict a slower motion, bringing the storm near the northern Lesser Antilles 6 - 7 days from now. Given the steady increase in organization of Gaston's remains today and high degree of model support for regeneration, I expect Gaston will be a tropical storm again, early next week.

99L
A tropical wave (99L) between the coast of Africa and the Cape Verdes Islands, is moving northwestward at about 10 mph. The wave has a bit of spin to it, and a modest amount of heavy thunderstorms. Wind shear has dropped to 20 - 25 knots, and will decrease to the moderate range, 10 - 20 knots, Saturday through Monday. The system will move over the Cape Verdes Islands over the weekend, bringing gusty winds and heavy rain squalls. NHC is giving the wave a 30% chance of developing by Sunday afternoon. Several models develop 99L into a tropical depression, but head it northwest into a region of very high wind shear that destroys the system by Wednesday.

Next post
I'll have an update Saturday by 1pm.

Jeff Masters