Hurricane Intensity & Terminology

Intensity Terms

Hurricanes are rated by wind intensities on a scale developed in the late 1960s by engineer Herbert S Saffir and meteorologist Robert H. Simpson. Known as the Saffir Simpson Scale, hurricanes are categorized depending on sustained winds.

  • 74 to 95 miles per hour (mph) winds Minimal Damage Expected
  • 96 to 110 mph winds Moderate Damage Expected
  • 111 to 130 mph winds Extensive Damage Expected
  • 131 to 155 mph winds Extreme Damage Expected
  • 150 mph winds and greater Catastrophic Damage Expected

Storm Surge

Winds are not the only danger during a hurricane - storm surge can also cause extreme danger to life and property. Storm surge is the abnormal rise of water generated by a storm. This surge is in addition to any normal tide range that occurs daily. The combination of normal tide and storm surge is known as Storm Tide.

  • Hurricane Camille in August 1969 produced a 24-foot storm tide along the Mississippi Coast.
  • Hurricane Katrina in 2005 produced a 27-foot storm tide also along the Mississippi Coast.

Watch & Warning Explanations 

Prior to any hurricane actually making landfall anywhere along a coast, these terms will be used by local emergency officials if your area could be impacted:

  1. Tropical Storm Watch - a watch is issued along a stretch of coastline when tropical storm conditions are POSSIBLE in the next 48 hours.
  2. Tropical Storm Warning - a warning is issued along a stretch of coastline when tropical storm conditions are EXPECTED in the next 36 hours.
  3. Hurricane Watch - a hurricane watch is issued for a stretch of coastline when hurricane conditions are POSSIBLE within the next 48 hours.
  4. Hurricane Warning - a warning is issued for a stretch of coastline when hurricane conditions are EXPECTED within the next 36 hours.

Hurricane Terminology

Easterly wave: A wavelike disturbance in the tropical easterly winds that usually moves from east to west. Such waves can grow into tropical depressions.

Extratropical cyclone: A storm that forms outside the tropics, sometimes as a tropical storm or hurricane changes. See table below for differences between extratropical and tropical cyclones.

Eye: The low-pressure center of a tropical cyclone. Winds are normally calm and sometimes the sky clears.

Eye wall: The ring of thunderstorms that surrounds a storm’s eye. The heaviest rain, strongest winds and worst turbulence are normally in the eye wall.

Hurricane: A tropical cyclone with winds of 74 mph or more. Normally applied to such storms in the Atlantic Basin and the Pacific Ocean east of the International Date Line.

Knot: A measure of speed. It is one nautical mile per hour. Never refer to "knots per hour" unless you want to describe acceleration. A nautical mile is one minute of one degree of latitude and is slightly longer than the ordinary, or statute, mile used in the United States. To convert nautical miles to miles or knots to miles per hour, multiply by 1.15. To convert miles to nautical miles or miles per hour to knots, divide by 1.15.

Millibar: A metric measurement of air pressure.

North Atlantic Basin (sometimes called just the "Atlantic Basin"): The Atlantic Ocean north of the equator, the Caribbean Sea and the Gulf of Mexico.

Subtropical Cyclone: A low pressure system that develops in subtropical waters (north of 20 north degrees latitude) and initially has non-tropical features, but does have some element of a tropical cyclone’s cloud structure (located close to the center rather than away from the center of circulation). Many of these systems are classified as "hybrid" storms.

Tropical Cyclone: A low-pressure weather system in which the central core is warmer than the surrounding atmosphere. See the table below for differences between tropical and extratropical cyclones. The term "tropical cyclone" is also used in the Indian Ocean and around the Coral Sea off northeastern Australia to describe storms called "hurricanes" and "typhoons" in other areas.

Tropical Depression (TD): A tropical cyclone with maximum sustained winds near the surface of less than 39 mph. Tropical Depressions are listed only with a number, not a name.

Tropical Storm: Tropical cyclone with winds of 39 to 74 mph. In most of the world, a storm is given a name when it reaches tropical storm intensity.

Tropical Disturbance: Often the earliest stages of a tropical cyclone. Normally an organized area of thunderstorms that form in the tropics and persists for more than 24 hours. Low pressure might form at the surface, but winds around remain below 30 mph.

Tropical Wave: An area of relatively low pressure moving westward through the trade wind easterlies. Generally, it is associated with extensive cloudiness and showers, and may be associated with possible tropical cyclone development.