The National Oceanic and Atmospheric Administration defines a hurricane as "an intense tropical weather system with well-defined circulation and sustained winds of 74 mph (64 knots) or higher." In the western Pacific Ocean, hurricanes are called typhoons while similar storms in the Indian Ocean are called cyclones.
The 1-5 scale estimates potential property damage.
A Category 3 or higher is considered a major hurricane.
A hurricane warning indicates that tropical-storm-force winds of at least 74 mph are expected within 36 hours.
There are four stages of development: tropical disturbance, tropical depression, tropical storm, tropical cyclone (hurricane).
Tropical disturbance: Cloud columns develop into a cluster of thunderstorms.
Tropical depression: Thunderstorms intensify, with maximum sustained winds of 38 mph.
Tropical storm: Maximum sustained winds are between 39-73 mph. During this time, the storm becomes more circular in shape, with winds swirling around a calm center, known as the eye. This is when the storm is named.
Tropical cyclone (hurricane): Wind speeds reach 74 mph. The storm is at least 50,000 feet high and 125 miles across, rotating around an eye that spans 5-30 miles wide.
Category 1: Minimal hurricane
Winds 74-95 mph.
Storm surge 3-5 feet.
No significant damage to buildings. Damage primarily to unanchored homes, shrubbery and trees.
Some damage to poorly constructed signs and coastal road flooding with minor pier damage.
Category 2: Moderate hurricane
Winds 96-110 mph.
Storm surge 6-8 feet.
Some damage to buildings, mainly roofs, doors and windows. Considerable damage to shrubbery and trees with some trees blown down. Major damage to mobile homes. Extensive damage to poorly constructed signs and considerable damage to piers.
Small craft in unprotected anchorages may break moorings.
Power outages could last from several days to weeks.
Category 3: Extensive hurricane
Winds 111-130 mph.
Storm surge 9-12 feet.
Some structural damage to small buildings. Many large trees blown down. Rampant destruction of mobile homes in storms ranked category 3 or higher. Serious coastal flooding, damaging or destroying structures along the water.
Evacuation of low-lying residences within several blocks of the shoreline may be required.
Electricity and water may be unavailable for several days to a few weeks.
Category 4: Extreme hurricane
Winds 131-155 mph.
Storm surge 13-18 feet.
Extensive building damage to windows and doors as well as roof collapse in some small residences. Shrubs, trees and signs are blown down. Major damage to lower floors of buildings near coastline due to flooding, battering waves and floating debris. Major beach erosion.
Power outages could last from weeks to possibly months. Areas may be uninhabitable for weeks or months.
Category 5: Catastrophic hurricane
Winds greater than 155 mph.
Storm surge higher than 18 feet.
Complete roof failure on many residences and industrial buildings. Widespread destruction of structures less than 15 feet above sea level within 500 yards of shore. Low-lying evacuation routes cut off by rising water 3 to 5 hours before hurricane center arrives.
Advance evacuation of residential areas on low ground within 5-10 miles of the shoreline may be required.
Power outages could last for months. Area may remain uninhabitable for months.
There are ten regional lists of names worldwide: Atlantic, Eastern North Pacific, Central North Pacific, Western North Pacific/South China Sea, Australian Region, Nadi, Port Moresby, Jakarta, Southwest Indian Ocean and Northern Indian Ocean.
Using women's names for Atlantic storms was the practice until 1979, when male names were added to the mix.
Names associated with storms that have caused significant death and/or damage are retired from the list. After an active 2017 hurricane season, NOAA announced the names Harvey, Irma, Maria and Nate were being retired. Other names that have been removed include Camille (1969), Andrew (1992), Opal (1995), Floyd (1999), Ivan (2004), Katrina (2005), Ike (2008) and Sandy (2012). Once a name is removed, another name replaces it.