Tracking Canada's Deadly Storms

Tropical cyclones with winds that rotate at speeds of more than 103.6 kilometres per hour, hurricanes are devastatingly powerful storms that usually travel over a large area during their lifespan. As they make their way from Africa across the Atlantic Ocean to the east coast of North America and venture into the northern latitudes, they undergo significant behavioural changes--a phenomenon known as extra-tropical transition.

Meteorologists at the Canadian Hurricane Centre in Halifax, Nova Scotia, are on the leading edge of studies in extra-tropical transition, as well as in the danger that storm-induced waves and tides--known as "storm surges"--pose to coastal communities. They are using complex computer models and data from ships' logs, public archives and other historic records to diagnose these storms and better understand the physics that drives them. In January 1999, a scientist from China and a researcher from McGill University joined the team in Halifax to contribute their expertise to these studies for the next year.

What they have learned, so far, is that hurricanes move more like regular winter storms in northern latitudes than they do down south, where they tend to be more erratic. They also travel up to five times faster--a serious concern given the fact that a large number of small boats are on the water during the June-to-November hurricane season. While hurricane forecasting always requires extreme precision due to the concentrated impact of these storms, it is an even greater challenge in northern latitudes because effects vary from one side of a hurricane to the other--with stronger winds to the east and torrential rain to the west. It has also been found that, although hurricanes weaken as they pass over cooler waters, on rare occasions they interact with extra-tropical storm fronts and re-intensify. Hurricane Hazel, which caused 81 deaths and $100 million damage in southern Ontario in 1954, was such a hybrid.

Typical path of hurricanes off the coast of Africa; the storms gather energy as they cross the warm waters of the Atlantic Ocean.

Although few of the two or three hurricanes Canada's Atlantic provinces average per year make landfall, considerable damage has been caused in the past by torrential rains and high and forceful wind-driven waters that sweep the coastline where the eye of the storm approaches nearest. Pioneers in the study of storm surges, Environment Canada scientists have created the largest database on the subject on the Atlantic coast, using archival information and forecasts to identify areas that are most vulnerable to the effects of such a disaster. Water marks on buildings from the devastating Saxby Gale of 1869--the model of a worst-case scenario--indicate that ocean water levels reached two metres above the high tide mark. With sea levels rising and storms becoming more intense due to climate change, scientists estimate that such a storm today would cause sea levels to rise nearly a metre higher--causing widespread and intense flooding in heavily populated coastal areas and on low-lying farmland.

In addition to sharing information with the international hurricane community through the committees of the World Weather Research Program and World Meteorological Organization, Canada's Atlantic meteorologists are helping to ensure public safety at home by working closely with the National Hurricane Centre in Miami, Florida, issuing technical and public bulletins, and assisting emergency responders in contingency planning. By encouraging land-use planners to consider this information when developing flood plans, managing dikes and building coastal infrastructure, science is helping to mitigate the future impacts of these deadly storms.

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