A natural way to think of it would be analogous to the saffir-simpson hurricane scale that is based on maximum sustained wind speed.
At the time this was taken, Igor was centered in the Atlantic Ocean and slowly moving west-northwest with maximum sustained winds of 213kph.
Category one hurricanes have maximum sustained winds of at least 74 miles per hour. They usually won't cause any real damage to buildings.
The U.S. National Hurricane Center (NHC) reported that Irene had maximum sustained winds of 80 mph (130 kph), with higher gusts.
Over Fiji, Tropical Cyclone Tomas had maximum sustained winds of 115 knots (215 km/hr, 132 mph) and gusts up to 140 knots (260 km/hr, 160 mph).
Late Thursday, "Danny" was centered 485 miles from Cape Hatteras, North Carolina. Maximum sustained winds of 45 miles an hour.
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