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NOAA > NWS > CPHC Home Page > Hurricane Awareness Week > Hurricane Basics
Hurricane Awareness Week
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HISTORY HURRICANE HAZARDS FORECAST PREPARE ACT
Hurricane History
Hurricane History
Storm Surge
Storm Surge
High Winds & Tornadoes
High Winds & Tornadoes
Marine Safety
Marine Safety
Forecast Process
Forecast Process
Be Prepared
Be Prepared
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Sunday
26 May
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29 May
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31 May
Saturday
1 June

Hurricane Basics

The ingredients for a hurricane include a pre-existing weather disturbance, warm tropical oceans, moisture, and relatively light winds aloft. If the right conditions persist long enough, they can combine to produce the violent winds, incredible waves, torrential rains, and floods we associate with this phenomenon.

Each year, an average of 3-4 tropical cyclones will affect the Central Pacific. An average of ten tropical storms develop over the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico. Many of these remain over the ocean and never impact the U.S. coastline. Six of these storms become hurricanes each year. In an average 3-year period, roughly five hurricanes strike the US coastline, killing approximately 50 to 100 people anywhere from Texas to Maine. Of these, two are typically "major" or "intense" hurricanes (a category 3 or higher storm on the Saffir-Simpson Hurricane Scale).

What is a Hurricane?
A hurricane is a type of tropical cyclone, which is a generic term for a low pressure system that generally forms in the tropics. The cyclone is accompanied by thunderstorms and, in the Northern Hemisphere, a counterclockwise circulation of winds near the earth's surface. Tropical cyclones are classified as follows:

* Sustained winds
A 1-minute average wind measured at about 33 ft (10 meters) above the surface.

** 1 knot = 1 nautical mile per hour or 1.15 statute miles per hour. Abbreviated as "kt".

Tropical Depression
An organized system of clouds and thunderstorms with a defined surface circulation and maximum sustained winds* of 38 mph (33 kt**) or less

Tropical Storm
An organized system of strong thunderstorms with a defined surface circulation and maximum sustained winds of 39-73 mph (34-63 kt)

Hurricane
An intense tropical weather system of strong thunderstorms with a well-defined surface circulation and maximum sustained winds of 74 mph (64 kt) or higher

Hurricanes are categorized according to the strength of their winds using the Saffir-Simpson Hurricane Scale. A Category 1 storm has the lowest wind speeds, while a Category 5 hurricane has the strongest. These are relative terms, because lower category storms can sometimes inflict greater damage than higher category storms, depending on where they strike and the particular hazards they bring. In fact, tropical storms can also produce significant damage and loss of life, mainly due to flooding.

Hurricane Names

When the the winds from these storms reach 39 mph (34 kts), the cyclones are given names. Storm names are used to facilitate geographic referencing, for warning services, for legal issues, and to reduce confusion when two or more tropical cyclones occur at the same time. Through a vote of the World Meteorological Organization Region IV Subcommittee, cyclone names are retired usually when hurricanes result in substantial damage or death or for other special circumstances. You can see the names for storms originating in the Eastern, Central and Western Pacific here.



ADDITIONAL SAFETY INFORMATION

    Basic Hurricane Safety Actions
  • Know if you live in an evacuation area. Know your home's vulnerability to storm surge, flooding and wind. Have a written plan based on this knowledge.
  • At the beginning of hurricane season (June 1st), check the supplies for your disaster supply kit, replace batteries and use food stocks on a rotating basis.
  • During hurricane season, monitor the tropics.
  • Monitor NOAA Weather Radio. It is an excellent / official source for real-time weather information and warnings.
  • If a storm threatens, heed the advice from local authorities. Evacuate if ordered.
  • Execute your family plan
    WATCH vs. WARNING - KNOW THE DIFFERENCE
  • A HURRICANE WATCH issued for your part of the coast indicates the possibility that you could experience hurricane conditions within 36 hours.
    This watch should trigger your family's disaster plan, and protective measures should be initiated, especially those actions that require extra time such as securing a boat.
  • A HURRICANE WARNING issued for your area indicates that sustained winds of at least 74 mph are expected within 24 hours or less.
    Once this warning has been issued, your family should be in the process of completing protective actions and deciding the safest location to be during the storm.