Chapter 12 – Tropical and Hurricanes

Understanding Weather and Climate Aguado and Burt

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Hurricane Andrew

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1 Hurricanes?

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

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Where Hurricanes Occur

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2 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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3 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 ( 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 .

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4 In-Up-Out

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Warm–Core System

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5 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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6 Easterly Waves

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Hurricane Requirements

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

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7 Hurricane Movement

• Movement is erratic and difficult to predict.

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Hurricane Names

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8 Hurricane Damage

• Winds • • Inland and Coastal Flooding • Tornadoes

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Hurricane Winds

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9 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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10 Some Famous Hurricanes

• (1969) – Category 5 – impacted with 23 ft storm surge. • (1988) – Category 5 – lowest recorded pressure of 850 mb, affected , Cancun, • (1992) – Category 4 – affected south and • Galveston Hurricane (1900) – Category 4 – killed 6000 people in

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Hurricane Andrew

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11 Hurricane Andrew

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Hurricane Andrew

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12 Hurricane Gilbert

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Hurricane Gilbert

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