Hurricanes are evaluated in a number of ways. Storms are assigned a category based on winds, storm surge and barometric pressure, using the Saffir-Simpson scale.
Category 1 storms have winds of 74-95 miles per hour, making them the weakest of hurricanes. Even these storms can generate a storm surge of 4 or 5 feet above normal high tide.
Category 2 storms have winds of up to 110 miles per hour, and can push a storm surge of 6 to 8 feet.
Category 3 storm winds can reach 130 miles per hour. This is the cutoff for "major" hurricanes, with commensurate storm surge potential of 9 to 12 feet.
Category 4 winds can be as high as 155 miles per hour, and such a storm brings a 13 to 18 foot storm surge.
Category 5 storms, with winds greater than 155 miles per hour, are very rare. These monsters can have storm surges of over 20 feet. Only 2 such hurricanes have hit the U.S. this century - Camille in 1969 and Labor Day Storm of 1935.