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8B – Slide 1 Topic 8B: Hurricanes Online Lecture: Hurricanes ○ What Causes Hurricanes? ○ Structure of a Hurricane ○ Death and Destruction Hurricanes Names from Around the World ○ Hurricanes go by many names: – name comes from Huracan (meso-american God of wind) – also called: ● Typhoon (East Asia) ● Cyclone (Indian Ocean) ● “Willy-Willy” (Australia) 8B – Slide 2 Hurricanes are tropical storms which have become very strong (75+ mph winds). 8B – Slide 3 Strong Winds & Rain of Hurricanes are Fueled by Very Warm Ocean Water ○ lots of evaporation of ocean water warms the air above the ocean Air rises quickly owing to its low density. LOTS of air rises, LOTS of water condenses = LOTS of Rain Winds Rising air contains a lot of water vapor. Ocean Hurricane “season” is from June to the end of November. Why can hurricanes form as late as November? Draw on the Board Isn’t the water too cold? 8B – Slide 4 Spiral Shape of a Hurricane Warm, Rising Air Warm, Rising Air Air tries to move towards the center, but it bends away because of the Coriolis effect: it cannot go in directly in, but must spiral in slowly Hurricane Structure 8B – Slide 5 As the air spirals in, it is (1) warmed & picks up moisture from the ocean surface, (2) rises, (3) cools & loses its water as rain, (4) sinks back down, and begins the process (steps #1-4) again – it goes through it several times Eye “Eye Wall” where the winds are strongest 8B – Slide 6 Coasts in Danger Why do most hurricanes strike the east & southern coasts of the United States? Equator Hint: Think about winds and/or currents. Equator Death & Destruction Caused by Hurricanes 8B – Slide 7 ○ Damage property and kill people in a variety of ways: – strong winds – lots of rain (flooding) – “storm surge”: What causes the most deaths and damage? FEMA & Flood Ins. ● sea level rises (20+ feet) beneath the hurricane, so the shoreline is flooded by ocean water, like a very high high tide, carrying huge waves inland 8B – Slide 8 What Causes Storm Surge? ○ Hurricanes are zones of low atmospheric pressure, because warm air spreads out (“expands”), so there is less air above each location pressing down. ○ The sea surface goes down in places where it is pushed down strongly, but it must rise elsewhere where the downward push is weaker to compensate (the water has to go somewhere). Low Pressure Land High Pressure Storm Surge & the Winds of Hurricanes 8B – Slide 9 The strong winds of the hurricane pushes the “hill” of water into shallow water and up against the land. The water cannot go forward quickly enough and the water cannot go down, so it rises upwards.