Hurricanes cont.

HURRICANES CONTINUED...

The final stage is the hurricane stage!

Stage 4: Hurricane

Hurricanes have sustained one-minute winds of at least 74 mph, at an elevation of 10 meters. Winds in most hurricanes can become much stronger.

Hurricanes are categorized on a scale of 1 to 5 based on their wind speed, a scale known as the Saffir-Simpson hurricane wind scale, named after its originators, Herbert Saffir and Dr. Robert Simpson.

In developing tropical cyclones, strong thunderstorms occur. Air pressure drops at the surface of these storms. This low pressure attracts warm moist air from the ocean's surface. The Coriolis force causes the resulting low-level winds to spiral in a counterclockwise direction around the center of the low in the Northern Hemisphere, whereas winds swirl clockwise in the Southern Hemisphere.

Typically, an "eye" forms when the tropical cyclone reaches hurricane strength, but an eye is not necessary for a tropical cyclone to become a hurricane.

Another way to think of a hurricane is as a large heat engine. The fuel is moisture from warm ocean water. The moisture is converted to heat in the thunderstorms that form. Spiral rain bands that surround the tropical cyclone's core help feed the circulation more heat energy.

As air nears the center, it rises rapidly and condenses into clouds and rain. The condensation releases tremendous amounts of heat into the atmosphere. The result is lower surface pressure and strengthening winds.

In this way, the tropical cyclone's engine refuels itself, concentrating its power in a donut-shaped area, called the eye wall, surrounding the center. The eye wall typically contains the strongest surface winds.

Sinking air at the center clears the tropical cyclone of clouds and forms the "eye." Falling surface pressure can occur only if air mass is removed from the circulation center. This is accomplished by wind flowing away from the circulation in the upper atmosphere.

Thankfully with technology today, we have learned so much about hurricanes!

http://www.weather.com/