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Chapter 12 – Tropical Storms and Hurricanes

Understanding Weather and ClimateAguado and Burt

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Hurricane Andrew

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Hurricanes?

• Hurricanes are also called Typhoons and Tropical Cyclones in other portions of the world.– Hurricanes – Atlantic and Eastern Pacific– Typhoon – Western Pacific– Tropical Cyclone – Indian Ocean and Australia

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Where Hurricanes Occur

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Where Hurricanes Occur

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Trade Wind Inversion

• Massive high pressure regions occupy the majority of the Atlantic and Pacific Oceans.– Upper level air sinks on the eastern periphery of the

high pressure creating a subsidence inversion (Trade Wind Inversion)

– Air below the inversion is relatively moist and cool.

• Farther west the inversion disappears allowing for convection and the development of hurricanes in the western portion of the ocean basins.

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Hurricane Characteristics

• Winds greater than or equal to 74 mph • Typical sea level pressures of ~950 mb• Typical size of ~350 miles across

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In-Up-Out

• Air spirals inward in the lowest levels towards the low pressure and acquires warmth and moisture from the ocean.

• Air moves upward in the thunderstorms (rainbands and eyewalls) and releases latent heat through condensation.

• This provides a warm core aloft and results in high pressure which moves air outward from the center of the storm.

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In-Up-Out

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Warm–Core System

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Eye and Eyewall

• Eye – Area of clear or mostly clear skies, calm winds and low pressure.– Contains descending air (warmer, drier)– Typical size of ~15 miles– Contracting eye is an indication of strengthening

• Eyewall – Thunderstorms which surround the eye containing the highest precipitation rates and wind wind speeds

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Hurricane Formation

• Tropical disturbance – small cluster of thunderstorms

• Tropical depression – storms contains a closed circulation

• Tropical Storm – wind speeds greater than 37 mph

• Hurricane - wind speeds greater than 74 mph

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Easterly Waves

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Hurricane Requirements

• Warm Surface Water (>81°F)• Coriolis Force• Unstable Conditions• Minimal Wind Shear

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Hurricane Movement

• Movement is erratic and difficult to predict.

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Hurricane Names

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Hurricane Damage

• Winds• Storm Surge• Inland and Coastal Flooding• Tornadoes

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Hurricane Winds

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Hurricane Watches and Warnings

• Hurricane Watch – Prediction that hurricane conditions will reach land in more than 24 hours.

• Hurricane Warning – Prediction that hurricane conditions will reach land within 24 hours.

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Hurricane Intensity

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Some Famous Hurricanes

• Hurricane Camille (1969) – Category 5 –impacted Mississippi with 23 ft storm surge.

• Hurricane Gilbert (1988) – Category 5 – lowest recorded pressure of 850 mb, affected Jamaica, Cancun, Monterrey

• Hurricane Andrew (1992) – Category 4 – affected south Florida and Louisiana

• Galveston Hurricane (1900) – Category 4 – killed 6000 people in Texas

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Hurricane Andrew

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Hurricane Andrew

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Hurricane Andrew

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Hurricane Gilbert

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Hurricane Gilbert