Hurricanes 2010

Hurricanes  A tropical cyclone that occurs in the Atlantic.  Also a generic term for low pressure systems that develop in the tropics.  Starts as a tropical depression (winds less than 39mi/hr).  Becomes a tropical storm and is given a name when the winds exceed 39mi/hr.  Finally becomes a hurricane when the winds reach 74mi/hr.

How Hurricanes Form  Form in warm, tropical waters.  Water must be at least 80°F(27°C).  Needs warm, moist air and converging winds.  Has a large difference in air pressure.  Formed by the heat energy and as long as the water is warm are self-sustaining.  The moist, warm air circulates around a well defined center.  The lower the pressure at the center, the faster the winds will rush in to try to fill it.

Hurricane Formation

Parts Continued  Eye: center of the hurricane. Weather is calm, may be clear, and will have no rain.  Winds will come from the opposite direction after the eye passes.  Rain bands will move counter- clockwise around the eye. These bands with hurricane force winds can extend over 300 kilometers from the eye. So the storms can affect a wide area.

Parts of a hurricane

Hurricane Movement  Hurricanes are steered by the global winds.  So the storms in the tropics are steered to the west by the trade winds. When they get far enough north the westerlies take over and steer them east.  Once over land (or cold water), they lose strength as they no longer have a source of warm water to draw energy from.  Friction with the land can slow the winds down also. Hurricanes die out when over land or cold water as they have no energy to sustain them.

Saffir-Simpson Hurricane Scale  The Saffir-Simpson Hurricane Scale is a 1-5 rating based on the hurricane's present intensity (wind speed).  This is used to give an estimate of the potential property damage and flooding expected along the coast from a hurricane landfall.  Wind speed is the determining factor in the scale  Called Categories (Katrina was a Category 5 hurricane.)

Hurricane Damage  Hurricane can cause enormous damage when they come ashore.  While high winds do a lot of damage, flooding is more serious.  Heavy rains cause flooding, especially if the hurricane is slow moving.  Storm surge is even more serious. It is a dome of water caused by low pressure and high winds. If it coincides with the high tide, many coastal areas will be devastated.

Hurricane Names  Since at least 1945, the US Navy and later the Air Force started naming tropical cyclones.  At first they used exclusively English female names, but since 1978 have started to alternate male and female names (alphabetically).  Different areas of the world tend to use local names for their areas.

Hurricane Names  There is a six year list.  If they run out of names in a year they use the Greek alphabet.  Hurricanes that do significant damage will have their name retired.

Atlantic Hurricane Names

Typhoons and Cyclones

Tropical Storm Warnings  TROPICAL STORM WATCH - Tropical Storm conditions with sustained winds from mph are possible in your area within the next 36 hours.  TROPICAL STORM WARNING - Tropical Storm conditions are expected in your area within the next 24 hours.

Hurricane Warnings  HURRICANE WATCH - Hurricane conditions with sustained winds of 74 mph or greater are possible in your area within the next 36 hours. Time to think about evacuating!  HURRICANE WARNING - Hurricane conditions are expected in your area within 24 hours. Past time to evacuate!