The Other Hurricane Season


(Ocean Weather Service) – Each year there are, on average, about 6 hurricanes in the North Atlantic, 8 in the Eastern North Pacific and 17 Typhoons in the western North Pacific. Few people (outside of Mariners) realize that there is another season of hurricane winds that occurs over both the North Atlantic and the North Pacific Ocean and runs from  September to May. These storms do not track through the tropics, but instead are associated with the extratropical cyclones of the mid-latitudes.

Roch19571, CC BY-SA 4.0 <>,Hurricane_Belle via Wikimedia Commons
Hurricane Belle via Wikimedia Commons

Extratropical Storms

An extratropical cyclone, also called a mid-latitude cyclone, is a storm system that gets its energy from horizontal temperature gradients and is most often associated with frontal zones. Tropical cyclones, in contrast, are generated by the energy released as clouds and rain form in warm, moist, tropical air masses. Extratropical cyclones occur throughout the year and can vary widely in size from under 100 NM to over 2,500 NM. On average, extra-tropical cyclones last about 5 days, however, hurricane-force wind events when associated with these systems typically last 24hr or less.

Hurricane Force Storms

It had been long known that extratropical cyclones can sometimes produce hurricane force winds but not until the deployment of modern satellite technology did meteorologists discover that hurricane wind events were much more frequent than previously thought. The risk for a winter hurricane wind event begins to increase in September and October, peaks in December and January, then tapers off sharply in April and May, although quite infrequently we have observed them in each month of the year in the North Atlantic.

Each winter season has, on average, about 37 non-tropical hurricane force wind events occur over the North Pacific and about 45 events over the North Atlantic.NOAA Ocean Prediction Center  issues a “Hurricane Force Wind Warning”