SEVERE STORMS: HURRICANES

The Most Powerful Storms on Earth

Hurricanes: Get the FactsThe term Hurricane comes from Huracan, a god of evil recognized by the Tainos, an ancient aboriginal tribe from Central AmericaIn other areas hurricanes are known by other names including typhoons, cyclones and baguiosSustained winds of 155 mph or higherIntense rainfallStorm surgesThey can expend as much energy as 10,000 nuclear bombs in their lifetime

The Right Conditions for Formation

Warm ocean water (>80°F)Converging winds force air

upWhen they reach the top of

the storm, winds flow out Warm moist air rises to

make the clouds in the storm

Outside wind steer the hurricane and allow it to grow

Tropical DisturbanceHurricanes begin as clusters of clouds and thunderstorms

called tropical disturbances

Tropical Disturbances have: low-pressure areas and little or no rotation.

Most of these disturbances die out, but a few persevere down the path to hurricane status:

Latent heat released which warms the disturbanceThe air density then dropsWind speed increases as cooler air rushes in under

he less dense warm airThe Coriolis Effect causes the disturbance to

rotateThe incoming winds bring more moisture with

them, producing cloud activity which releases latent heat (feeds the storm)

The Tropical Disturbance requires wind and warm moist air to continue growing, this is like it’s “food”. As a Tropical storm builds and develops it goes through three distinct stages:

Tropical depression: wind speeds of less than 38 mph

Tropical storm: wind speeds of 39 to 73 mph

Hurricane: wind speeds greater than 74 mph

Anatomy of a Hurricane:

Eye: A hurricane's low-pressure center of relative calm

Eye Wall: The area surrounding the eye where the storm's most violent winds occur Rainbands: The bands of thunderstorms that circulate outward from the eye. These storms play a key role in the evaporation/condensation cycle that feeds the hurricane

Anatomy of a Hurricane

Death of a Hurricane

A hurricane dies when the storm encounters conditions that deny it the warm, moist air it requires

When it moves to cooler waters at a higher latitude, gradient pressure decreases, winds slow, and the entire storm is tamed, and it peters out in days.

When a hurricane hits land the important supply of warm, moist air also vanishes. Condensation and the release of latent heat diminishes, and the friction of an uneven landscape decreases wind speeds.

Hurricane Categories

Where They HappenMost Hurricanes form between 5 and 20 degrees N and S latitude

The North Pacific gets the most hurricanes each year with an average of 20 per year

The U.S. gets an average of 5 Hurricanes per year?