Atlantic Canada is affected by two main types of storms: the tropical cyclone (e.g. hurricanes) and the extratropical cyclone (e.g. Nor’easters).
Tropical cyclones develop in southern latitudes in the warmer months of June to November. These storms can track northward along the eastern North American seaboard where they usually weaken, but from time to time they affect Atlantic Canada as hurricanes, tropical storms or post-tropical storms. Hurricane Juan is an example of one storm which struck Nova Scotia in September 2003.
According to the IPCC Fourth Assessment Report (2007) it is likely that future tropical cyclones (i.e. hurricanes) will become more intense, with larger peak wind speeds and more heavy precipitation associated with ongoing increases of tropical sea surface temperatures. Analyses of model simulations suggest that for each 1°C increase in tropical sea surface temperatures, hurricane surface wind speeds will increase by 1 to 8% and core rainfall rates by 6 to 18 % according toWeather and Climate Extremes in a Changing Climate, Regions of Focus: North America, Hawaii, Caribbean, and U.S. Pacific Islands.
Extratropical cyclones (ETC) develop in mid-northern latitudes,between approximately 30°N-60°N,along a boundary between warm and cold air masses. These storms aremost frequent and intense between October and March. Over land or near populous coastlines, strong or extreme ETC events generate some of the most devastating impacts associated with extreme weather and climate, and have the potential to affect large areas and dense population centers. Over the ocean, strong ETCs generate high waves that can cause extensive coastal erosion when combined with storm surge as they reach the shore, resulting in significant economic impact. Rising sea level extends the zone of impact from storm surge and waves farther inland, and will likely result in increasingly greater coastal erosion and damage from storms of equal intensity.
According to the US Climate Change Science Program in their 2008 Synthesis and Assessment Product Weather and Climate Extremes in a Changing Climate, Regions of Focus: North America, Hawaii, Caribbean, and U.S. Pacific Islands,the balance of evidence suggests that there has been a northward shift in the tracks of strong low pressure systems (storms) in the North Atlantic basin and that over most regions, precipitation is likely to be less frequent but more intense, and precipitation extremes are very likely to increase. There are likely to be more frequent deep low-pressure systems (strong storms) outside the tropics, with stronger winds and more extreme wave heights.
Famous examples of this type of storm are the Groundhog Day storm of February 1976, the Halloween Storm of 1991 and the "Storm of the Century" in March 1993.
For examples of storm impact in Atlantic Canada visit: