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Tuesday, September 21, 2010

TSR Storm Alert - Hurricane IGOR to strike Canada

Tropical Storm Risk is reporting a 100% likihood that Hurricane Igor will strike the Canadian maritime provinces as a Category 1 hurricane. Igor appears on track to scrape the eastern edge of Newfoundland and the eye may even pass over or very close to the city of St. John's. The forecast calls for Igor to remain at hurricane strength as it progresses north past Newfoundland into Baffin Bay potentially brushing against the southwestern coast of Greenland or making landfall in the far northern areas of Nunavut Province.

Graphic courtest of Weather Underground

It is very unusual for a storm to remain this strong so far north. The computer models show a fair amount of scatter in the potential paths of the storm but it appears that Igor will likely enter Baffin Bay and make landfall in northern Canada as a tropical storm. There is a slight chance that Igor will head into the Northern Atlantic but this appears to be slim.

Graphic courtesy of Spaghetti

Hurricane Igor heads north, all the way to Greenland?(Christian Science Monitor)
Between next Thursday morning and Friday morning, forecasters at the National Hurricane Center in Miami say they expect Igor to make landfall on the southern tip of Greenland, perhaps with tropical-storm-force winds, then to move into the interior as a "post-tropical" depression.

The label "post-tropical" refers to a shift in a storm's energy source. In Igor's case, its energy source is expected to shift by Tuesday morning.

As a tropical cyclone, Igor draws its energy from heat. That heat is released as water condenses from vapor to cloud droplets as the vapor rises higher into the atmosphere and cools, forming powerful thunderheads. As the storm moves north, it encounters cooler water and draws its energy from the difference in temperature between the storm itself and a cooler mass of air sweeping into the North Atlantic from middle and high latitudes. At that point, Igor earns the post-tropical tag.

These storms can still be dangerous, since they continue to pack gale-force winds. These winds typically blow at altitudes of from several hundred feet to a little over 1,000 feet. They can trigger significant wind damage if the storm encounters an environment that encourages mixing between air layers near the ground and the layers carrying the gale-force winds.

By the time Igor draws even with southern Newfoundland overnight Tuesday, it is expected to pack hurricane-force winds, although it will have become post-tropical. Igor's track is expected to come close enough to the Canadian province's southeastern tip, prompting the government to issue tropical-storm warnings for that area.

N Atlantic: Storm Alert issued at 21 Sep, 2010 9:00 GMT

Hurricane IGOR (AL11) is forecast to strike land to the following likelihood(s) at the given lead time(s):
Red Alert Country(s) or Province(s)
probability for CAT 1 or above is 100% within 9 hours
probability for TS is 100% currently
probability for CAT 1 or above is 35% in about 69 hours
probability for TS is 100% in about 33 hours
Red Alert City(s) and Town(s)
St John's (47.6 N, 52.7 W)
probability for CAT 1 or above is 100% within 9 hours
probability for TS is 100% within 9 hours

Yellow Alert Country(s) or Province(s)
St. Pierre and Miquelon
probability for TS is 100% currently
Yellow Alert City(s) and Town(s)
Grand Falls (48.6 N, 55.4 W)
probability for TS is 100% within 9 hours
Godthab (64.3 N, 51.6 W)
probability for CAT 1 or above is 10% in about 45 hours
probability for TS is 100% in about 45 hours

Note that
Red Alert (Severe) is CAT 1 or above to between 31% and 100% probability.
Yellow Alert (Elevated) is CAT 1 or above to between 10% and 30% probability, or TS to above 50% probability.
CAT 1 means Hurricane strength winds of at least 74 mph, 119 km/h or 64 knots 1-min sustained.
TS means Tropical Storm strength winds of at least 39 mph, 63 km/h or 34 knots 1-min sustained.

For graphical forecast information and further details please visit

This alert is provided by Tropical Storm Risk (TSR) which is sponsored by UCL, Aon Benfield, Royal & SunAlliance, Crawford & Company and Aon Benfield UCL Hazard Research Centre. TSR acknowledges the support of the UK Met Office.

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