Hurricane Isabel Summary

Storm Summary

Hurricane Isabel formed in the central Atlantic Ocean on September 6th, 2003. Isabel first moved on a west-northwest track and eventually westward north of the Caribbean and Bahamas. During that period the hurricane maintained the most severe category 5 status on two separate occasions and was at least a category 4 storm for several days from September 9th to the 15th. The storm produced fascinating eye and eyewall features during its most intense phase. Such features included multi-vortex structures leading to spoked patterns in the cloud within the eye. Isabel slowed down after turning toward the northwest on the 14th. There was also a breakdown of the core into concentric eyewalls that lead to weakening. The slower motion also churned up cooler waters that prevented Isabel from any further intensification. In fact, the hurricane continued to weaken as it headed toward the North Carolina coast. Isabel made landfall as a category 2 storm with maximum sustained winds near 85 knots around 17 UTC at Ocracoke Island between Cape Hatteras and Cape Lookout. The storm continued to push inland, wreaking havoc in North Carolina, Virginia, Maryland, Washington and areas north.

Isabel crossed Lake Erie as a tropical storm around midday on Friday, September 19th. The weakened tropical storm brought sustained winds of 35 knots (gusts to 45 knots) over Lake Erie and Lake Ontario. Within a couple hours after arriving on the Ontario side of Lake Erie (just west of Long Point), winds dropped below 35 knots and Isabel became extratropical as a short-wave trough approached from the west. An associated surface cold front later merged with the remnants of Isabel and the combined system underwent moderate deepening and moved into northern Ontario and Quebec.

Impact in Ontario

There was no question that weather in southwestern Ontario took on the nature of a tropical storm. In Toronto, there were heavy rains accompanied by gusty winds during the morning hours of Friday September 19th. The worst of the weather at Pearson International was just before 10:00 am with torrential rain and wind gust of 72 km/h.

Such was the scene across southwestern Ontario from Toronto to Windsor. There were many reports of power outages from large limbs falling onto lines. There were spotty reports of downed trees and flooding. Also with a tropical storm airmass came warm and muggy conditions. Within the heavy rain and wind area, temperatures and dew points were near 19 or 20°C. Over eastern sections, temperatures rose to the mid-twenties under partly sunny skies.

The strong pressure gradient that was set up between the north side of Isabel and a large high over eastern Canada created strong easterly winds across Lake Ontario and eastern Lake Erie. Waves built to near 4 metres (13 feet) at the western end of Lake Ontario. Waves were seen crashing onto the shore and over seawalls near Hamilton. Spray from these waves was flying through the air onto streets thanks to sustained winds of 30 knots (55 km/h) gusting to 40 knots (73 km/h). The storm prompted several weather warnings including gale force wind warnings for Lake Ontario and Lake Erie as well as Lake Huron/Georgian Bay. Wind warnings were in effect for parts of the lakeshores and heavy rainfall warnings were in place over southwestern Ontario near and just west of the storm track for amounts of 30 to 50 mm.

Convair research flight

Participating in research flights is critical in helping meteorologist understand more about the behaviour of transitioning system, which in turn will lead to improving forecast techniques and timely warnings.

Given that Isabel was expected to undergo extratropical transition, a group of Canadian researchers organized a flight into tropical storm Isabel over southern Ontario on Friday September 19th (between 1600 and 1930 UTC). This was the first over-land extratropical transition the team had flown, but the goals were similar to other (oceanic) extratropical transition missions (Michael, October 2000 and Karen, October 2001), which was to diagnose the structure of the storm undergoing extratropical transition by collecting data from radar and dropsondes (weather sensors).

The Convair-580 aircraft departed from its home base at the National Research Council hangar in Ottawa at 11:45 am EDT on Friday. The flight lasted about 3.5 hours and covered Lake Ontario and Lake Erie, flying just south of the surface centre position. There was moderate icing on the aircraft while flying through the heaviest area of precipitation (eastern Lake Erie) which built up to an inch on the leading edge of wing-mounted probes. Ice had accumulated on the propellers forcing the pilot to drop to the freezing level which was around 15 000'. One large chunk of ice was shed from the propeller on the right side of the aircraft and took a couple segments of paint off the side of the fuselage.

In addition to the flight crew and research scientists there was also a camera crew gathering footage aboard the aircraft for a documentary under production on extratropical transition storms. In conjunction with the Convair flight, a series of extra radiosondes were released from various stations across southern Ontario including Maniwaki and Montreal, Quebec. Ron McTaggart-Cowan (McGill University) was releasing sondes from Trenton and also providing numerical weather prediction output for the flight and forecast operations.

Date modified:

2017-07-25