Earl hits Nova Scotia but spares New England; Gaston still a threat

Tropical Storm Earl roared ashore over western Nova Scotia late this morning, bringing heavy rain and tropical storm force winds to much of the province. The capital of Halifax recorded sustained winds of 51 mph, gusting to 75 mph at 12:48pm AST this afternoon, and the power is out to tens of thousands of residents in Nova Scotia. Winds were stronger at McNabs Island, in Halifax Harbor, where sustained winds of 64 mph, gusting to 76 mph, occurred at noon AST.

Earl's center passed about 100 miles southeast of Nantucket, Massachusetts, at 1am EDT this morning, and the winds on the weak left side of the storm never reached sustained tropical storm strength (39 mph) at any New England land station. The peak wind gust in Massachusetts may have been the 58 mph gust recorded on Cape Cod 5 miles south-southeast of Barnstable early this morning. Earl did bring some very high waves to New England; waves at the buoy 60 miles southeast of Nantucket peaked at 27 feet early this morning. Heavy rain from Earl--over five inches in some locations--caused localized flooding and road closures on Cape Cod and on Marthas Vineyard.


Figure 1. Hurricane Earl as seen from the International Space Station on Thursday, September 2, 2010. Image credit: NASA astronaut Douglas Wheelock.


Figure 2. Radar estimated rainfall from Earl from the Cape Cod radar.

Gaston a threat to develop
Recent satellite imagery shows that Gaston's remains have developed a well-organized surface circulation, but not enough heavy thunderstorm activity to be considered a tropical depression. A large amount of dry air surrounds Gaston's remains on all sides, 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 four days, then fall to the low range. The winds creating the shear are coming from the east, where a tongue of dry air has intruded. These easterly winds will be able to drive the dry air into Gaston's core, disrupting it, unless the storm can find a moister environment. It is also possible that Gaston may be able to protect its core by wrapping moisture around to its east side; recent visible satellite imagery shows a band of moisture wrapping around along Gaston's south side. If this process is successful, Gaston may have a good chance of becoming a tropical depression on Sunday. I suspect there is too much dry air in Gaston's environment for Gaston to develop into a tropical depression today. The atmosphere is moister near the Lesser Antilles Islands, and Gaston has a better chance of developing on Monday when it finds this moister environment. NHC is giving Gaston a 70% chance of regenerating into a tropical depression by Monday. The models are in fairly good agreement bringing Gaston though the central or northern Lesser Antilles Islands on Tuesday. The storm should then slow down and head more to the west-northwest on Wednesday and Thursday, in response to a large trough of low pressure expected to move off the U.S. East Coast. Puerto Rico and the Dominican Republic might be at risk of a strike by a reborn Tropical Storm Gaston by Thursday, if the storm follows a more southerly track over the next few days.


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

Gulf of Mexico disturbance
A concentrated area of heavy thunderstorms has developed over the extreme southwestern Gulf of Mexico, in the Bay of Campeche. This disturbance is under a low 5 - 10 knots of wind shear, and has a 20% chance of developing into a tropical depression by Monday, according to NHC. The disturbance is headed northwest at 5 - 10 mph, but could turn more to the north-northwest and bring heavy rains to the Texas/Mexico border region on Monday, according to the latest run of the GFS model.

99L
A tropical wave (99L) near the Cape Verdes Islands off the coast of Africa is moving northwestward at about 10 mph. The wave has a bit of spin to it, but not much heavy thunderstorm activity. This system is under moderate wind shear, but is headed towards a region of high wind shear northwest of the Cape Verdes Islands. This shear will very likely destroy the disturbance by Tuesday. NHC is giving 99L a 20% chance of developing into a tropical depression by Monday afternoon.

Elsewhere in the tropics
The GFS and ECMWF models are predicting development 3 - 6 days from now of a tropical wave that hasn't emerged from the coast of Africa yet.

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

Jeff Masters