Weather and Climate Unit Investigative Science

* Normally peaceful, tropical oceans are capable of producing one of Earth’s most violent weather systems—tropical storms and Hurricanes!

* During summer and fall, the tropics experience conditions ideal for the formation of large, rotating, low-pressure tropical storms. * In different parts of the world, the largest of these storms are called hurricanes, typhoons, and cyclones.

* Favorable conditions for cyclone formation exist in all tropical oceans except the South Atlantic and the Pacific Ocean off the west coast of South America. The water in those two areas are cooler and have nearly permanently stable air. Click here for video: What are hurricanes, typhoons and cyclones?

This map shows where every hurricane (or cyclone) has tracked from across the Earth’s oceans. Click here for video: how hurricanes form

* Two conditions are needed to form a cyclone (or hurricane): * 1) An abundant supply of warm ocean water * 2) Some sort of mechanism to lift warm air and keep it rising * Cyclones thrive on the tremendous energy in warm, tropical oceans.

* Latent (stored) heat is stored in water vapor. This latent heat is later released when the air rises and the water vapor condenses. * This heat fuels the formation of larger and larger tropical storms and hurricanes.

* The air usually rises because of some sort of existing weather disturbance moving across the tropics. * Many of these disturbances originate along the equator. * Only a small percentage of tropical disturbances develop into cyclones.

Warm, humid air rises from the surface of the ocean, then cools at high altitudes an falls back to the surface. In the center of the storm, the rising column of air leaves a low pressure area (L) that is the eye of the storm.

* The first indication of a building tropical storm is a moving tropical disturbance. * A tropical disturbance is a large thunderstorm with sustained winds of km/hour. * The Coriolis Effect causes the moving air to turn and spiral.

* A tropical storm forms as winds increase to speeds of km/hour, strong thunderstorms develop and become well defined. Click here for Hurricane Animation: prod.cdn.s3.amazonaws.com/media/assets/wgbh/ess05/ess05_int_hurrlife/index.htmlhttp://pbs.panda- prod.cdn.s3.amazonaws.com/media/assets/wgbh/ess05/ess05_int_hurrlife/index.html

* With sustained winds of 118 km/hour, an intense tropical weather system with well- defined circulation is now a cyclone (hurricane). Click here for video: Hurricanes 101http://video.nationalgeographic.com/video/101- videos/hurricanes-101http://video.nationalgeographic.com/video/101- videos/hurricanes-101

* The storm develops around a calm center, called the eye. * The eye of the cyclone is a span of 30 to 60 km of calm weather and blue sky. * The strongest winds of the cyclone are concentrated in the eyewall—a tall band of winds that surround the eye. Click here for video of the eyewall of Hurricane Katrina:

* A cyclone will last until it can no longer produce enough energy to sustain itself. * This usually happens when the storm has moved over land or over colder water.

* There are many dangers associated with hurricanes: * Storm Surge * High Winds * Heavy Rains and Flooding * Tornadoes * Rip Tides

* Storm surge is water pushed towards the shore by the force of the winds surrounding a hurricane. * The storm surge can combine with normal tides and increase the water level by 30 feet or more. * Storm surge can cause extensive damage, flooding, and loss of life. * Click here for a video about storm surge:

* n 2005, the storm surge from Hurricane Katrina left some parts of New Orleans more than 20 feet under water. * Much of New Orleans was below sea level and protected by levees, massive earthen flood walls designed to keep high waters out of the city. * The surge overtopped the levees, destroying homes and killing hundreds of people. Engineers caution that Katrina wasn’t even a direct hit on New Orleans. They are working to protect the city from the next big storm surge. Click here for video: Hurricane Katrina, National Geographic: formation

* Strong winds are the most common means of destruction associated with hurricanes. Their sometimes continuous barrage can uproot trees, knock over buildings and homes, fling potentially deadly debris around, sink or ground boats, and flip cars.

Saffir- Simpson Scale of Wind Speed and Damage from Hurricanes