Severe weather

1. Severe weather Concept 1: hurricanes are large, whirling low-pressure systems that form over warm ocean water in the tropics Concept 2: tornadoes are violently rotating columns of air, in contact with the surface of the earth, visible as a rope-shaped or wedge-shaped cloud

2. Hurricanes • Are large, whirling low pressure systems that form over warm ocean water in the tropics; • They bring extremely high winds, thunder, lightening, large amounts of rain and tornadoes; • If north of the equator they spin in the counterclockwise direction due to the earth’s spin, called the Coriolis effect.

3. Hurricane Formation • Form in warm ocean water; • when a large mass of unstable warm air begins to rise and cool, clouds begin to form; • The rising mass of air starts to spin; • If the spinning winds increase in speed, the unstable mass becomes a tropical cyclone.

4. Hurricane categories • Wind speed are used to categorize hurricanes; • Category I: 74-95 mph, 119-153 kph; • Category II: 96-110 mph, 154-177 kph; • Category III: 111-130mph, 178-209 kph; • Category IV: 130-155 mph, 210-249 kph; • Category V: Most severe storm, +155mph, +249 kph.

5. Tornadoes • Are very destructive storms that form over land; • They cause great damage with winds that spin up to 300mph (480 kph); • Spring and summer seasons are the most active times for tornadoes; • Tornado Alley-those parts of the Great Plains and Midwest where sightings are frequent.

6. Tornado Formation • Occur in very severe thunderstorms where winds blow at different heights and at different speeds; • This causes a funnel cloud to form; • Tornado winds spiral, or spin in counterclock direction around the center or eye of a low pressure area;