Hurricane Lee, still at hurricane strength after nine days, is on its final approach to a landfall in southwestern Nova Scotia, expected to occur on Saturday. Lee is a large and powerful storm that will bring hazardous heavy rains, tree-felling winds, and coastal flooding to a large portion of Atlantic Canada and New England.
Lee battered Bermuda for much of the day Thursday, bringing pounding surf and sustained tropical-storm-force winds that caused widespread power outages. The upper-level clouds of Lee began spreading over New England and Atlantic Canada Friday morning, and rains from the hurricane should begin to affect eastern Massachusetts and Nova Scotia on Friday night.
Forecast for Lee
As of 11 a.m. EDT Friday, Lee was a Category 1 hurricane with top sustained winds of 80 mph and a central pressure of 962 mb, headed north-northeast at 18 mph. Satellite imagery showed that Lee was increasingly taking on the appearance of a nor’easter, becoming increasingly asymmetric: Most of its thunderstorm activity was on its north side as dry air wrapped around its south side. This process will continue as wind shear ramps up and the waters beneath the storm grow colder, though Lee’s large size will help keep the weakening process gradual rather than sudden. The National Hurricane Center predicts that Lee will come ashore in southwest Nova Scotia as a borderline Category 1 hurricane/tropical storm with 75 mph winds on Saturday afternoon, when it will likely be categorized as a post-tropical storm. The current and predicted structure of Lee on Saturday suggest that there will be little precipitation on the backside of the storm after landfall.
Lee’s rains will fall atop ground that is largely saturated after one of the region’s wettest summers on record, so localized flooding will be a definite risk, even well inland. The sodden ground will make it easier for Lee’s winds to bring down trees and power lines, and residents should be prepared for the possibility of significant power outages. Although some are comparing Lee’s future impact to that of a winter nor’easter, the trees have all their leaves at present and will be more prone to blowing down than in the winter.
Because of the high tidal range in this part of the world, coastal flooding impacts from Lee’s one to three-foot storm surge will mainly occur near the time of high tide. High tide at Boston is around 1 p.m. EDT Saturday; high tide at Eastport, Maine, on the Canadian border, is at 12:31 p.m. EDT Saturday and 12:48 a.m. EDT Sunday. Water levels in Massachusetts at Chatham on Cape Cod, Boston, and Nantucket were already about 0.5 feet above normal on Friday morning, and a live webcam on Cape Cod was showing some impressive surf.
Lee is a very large hurricane
Lee is very impressive in size, with hurricane-force winds that extend out up to 105 miles from the center and tropical-storm-force winds that extend out up to 320 miles. On Saturday, this large wind field will likely subject an unusually extensive stretch of the coast to tropical storm-force winds: from eastern Massachusetts to central Nova Scotia, including the coasts of New Hampshire, Maine, and New Brunswick (Figure 1 above).
Margot now a tropical storm
The least worrisome of Friday’s three tropical cyclones in the Atlantic is Tropical Storm Margot, still spinning in the remote central North Atlantic about 600 miles west of the Azores. Margot was downgraded from hurricane status on Friday morning, and its top sustained winds were down to 65 mph as of 11 a.m. Friday. Margot remained well organized, with distinct bands wrapping around its center and clusters of intense thunderstorms at its core, but the banding was increasingly skeletal as dry air infiltrates the system. Midlevel relative humidity will drop from around 45% to around 35% by this weekend, and northerly winds aloft will continue to exert strong wind shear and push more dry air into the storm. Sea surface temperatures beneath Margo should remain around 26-27 degrees Celsius (79-81°F), just warm enough to support Margo as a tropical storm.
Ensemble models agree that Margot will continue a compact clockwise loop over the weekend, circling the ridge that is helping to steer Lee, and then accelerate eastward early next week. Margot is predicted to remain a weakening tropical storm until it reaches cooler waters and becomes post-tropical sometime next week.
Tropical Depression 15 forms in the central tropical Atlantic
The disturbance known as 97L became Tropical Depression 15 at 11 a.m. Friday, in the waters of the tropical Atlantic midway between the Lesser Antilles and Cabo Verde Islands. Satellite images early Friday afternoon showed that TD 15 was steadily growing more organized, with intensifying curved bands of heavy thunderstorms wrapping around the surface circulation center.
As it moves west-northwest to northwest at 10-15 mph over the next several days, TD 15 will have favorable conditions for development: light to moderate wind shear (5-15 knots), sea surface temperatures of 29-30 degrees Celsius (84-86°F), and a moist atmosphere. The National Hurricane Center is predicting that TD 15 will become Tropical Storm Nigel by Friday night and Hurricane Nigel by Sunday night. The top models continue to be in strong agreement that steering currents will take TD 15 toward the northwest into the remote central Atlantic, likely making it a “fish” storm of concern only to marine interests. However, residents of Bermuda will want to monitor forecasts for TD 15, as the storm may come close to the island next week.
Next tropical wave
The GFS and European models are predicting that another tropical wave will emerge from the coast of Africa on Wednesday and then develop late next week in the central tropical Atlantic. This wave will potentially follow a more westerly course than 97L and will bear watching in case it threatens the Caribbean islands. In its 8 a.m. EDT Friday Tropical Weather Outlook, the National Hurricane Center gave this future system two-day and seven-day development odds of 0% and 20%, respectively. The next name on the Atlantic list of storms after Nigel is Ophelia.
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