Glossary of Terms and Categories

A glossary of hurricane-related terms used by the National Weather Service and The National Hurricane Center:

Hurricane watch: Issued when there is a threat of hurricane conditions within 36 hours.

Hurricane warning: When sustained winds of 74 mph or more are expected in a specified area in 24 hours or less.

Gale warnings: When winds of 39 to 54 mph are expected.

Flash flood warning: A flash flood is imminent or occurring - take immediate action.

Knot: A measure of speed. It is one nautical mile per hour. One knot equals 1.15 miles per hour or 1.9 kilometers per hour.

Millibar: A metric measurement of air pressure.

Storm surge: A dome of water that builds up as a hurricane moves over water. As this water comes ashore with the storm, it causes flooding that is usually a hurricane’s biggest killer.

Storm tide: The actual level of the seawater resulting form the tide combined with the storm surge.

The Saffir-Simpson scale: Used to estimate the potential property damage and coastal flooding. The scale is determined by wind speed, since storm surge sizes depend on the slope of the continental shelf. It is measured in categories from 1, being the weakest to 5, which is strongest with potential for catastrophic damage.

Category 1: Winds 74-95 mph. Storm surge 4 to 5 feet above normal. Damage primarily to unanchored mobile homes, shrubbery and trees. Some damage to poorly constructed signs and piers.

Category 2: Winds 96-110 mph. Storm surge 6 to 8 feet above normal. Some roof, door and window damage of buildings. Considerable damage to mobile homes, small watercraft, trees, poorly constructed signs and piers. Flooding of coastal and low-lying areas.

Category 3: Winds 111-130 mph. Storm surge 9 to 12 feet above normal. Some structural damage to small residences. Mobile homes destroyed and large trees blown down. Coastal flooding destroys smaller structures and floating debris damages larger structures.

Category 4: Winds 131-155 mph. Storm surge 13 to 18 feet above normal. Wall failures and roof collapses on small residences, and extensive damage to doors and windows. Complete destruction of mobile homes. Major coastal flooding.

Category 5: Winds greater than 155 mph. Storm surge greater than 18 feet above normal. Complete roof failure on many residences and industrial buildings. Major damage to lower floors of all structures located less than 15 feet above sea level and within 500 yards of the shoreline.

Massive evacuation of residential areas on low ground within 5 to 10 miles inland may be required.