An atmospheric closed circulation rotating counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

The relatively calm center of the tropical cyclone that is more than one half surrounded by wall cloud. This clear, calm area is the result of sinking air in the center of a tropical cyclone.

An organized band of cumuliform clouds immediately surrounding the center of a tropical cyclone. Eye wall and wall cloud are used synonymously. The eye wall typically contains the strongest winds and most violent weather within a tropical system.

A term used in advisories and tropical summaries to indicate that a cyclone has lost its "tropical" characteristics. This usually happens once a system moves from mid latitudes to high latitudes and changes from a "warm core" to a "cold core" system.

An interaction where tropical cyclones within a certain distance (300 - 750 nautical miles, depending on the sizes of the cyclones) of each other begin to rotate about a common midpoint. Typically, one of the cyclones becomes dominant while the other weakens.

A warning of 1-minute sustained winds in the range of 34-47 knots (39-54 mph). The warning can be issued either for predicted winds in this range or winds that are already occurring. It is not necessarily associated with tropical cyclones.

A high wind warning is defined as 1-minute average surface winds of 35 knots or greater (40 mph or greater) lasting for 1 hour or longer, or winds gusting to 50 knots or greater (58 mph or greater) regardless of duration that are either expected or observed over land.

A warm-core tropical cyclone in which the maximum sustained surface wind is 64 knots or greater (74 mph or greater). The term hurricane is used for Northern Hemisphere cyclones east of the International Dateline to the Greenwich Meridian. The term typhoon is used for Pacific cyclones north of the Equator, west of the International Dateline.

A public release prepared by local National Weather Service offices in or near a threatened area giving specific details for its county/parish warning area on (1) weather conditions, (2) evacuation decisions made by local officials, and (3) other precautions necessary to protect life and property.

The portion of the year having a relatively high incidence of hurricanes. The hurricane season in the Atlantic, Caribbean, and Gulf of Mexico runs from June 1 to November 30. The hurricane season in the Eastern Pacific basin runs from May 15 to November 30. The hurricane season in the Central Pacific basin runs from June 1 to November 30.