Understanding Hurricanes and Extratropical Cyclones

Cyclone

Area of low pressure with rotating winds.

Tropical Cyclones

Rotating thunderstorms over warm waters.

Extratropical Cyclones

Cyclones not formed over tropical waters.

Peak Wind Speed

257 km/h (160 mph) during Hurricane Katrina.

Barometric Pressure

902 mb peak; 920 mb at landfall.

Human Catastrophe

1,200 fatalities and $108 billion damage.

Levee Breach

Caused significant flooding in New Orleans.

Hurricane Katrina

One of the top five intense U.S. hurricanes.

Category 5

Highest hurricane classification before landfall.

Landfall Date

August 29, 2005, as a Category 3.

Storm Surges

Rise in sea level due to storms.

Tropical Depressions

Weakest form of tropical cyclones.

Hurricanes

Tropical cyclones in North America.

Typhoons

Tropical cyclones in Western Pacific.

Coriolis Effect

Apparent deflection due to Earth's rotation.

Typhoon

Chinese term for 'scary wind'.

Hurricane

Caribbean term for evil wind god.

Saffir-Simpson Scale

Classification system for hurricane intensity.

Tropical Disturbance

Initial stage of a hurricane with thunderstorms.

Tropical Depression

Winds increase, forming a low-pressure center.

Tropical Storm

Winds reach 63 kmph (~39 mph).

Eyewall

Central intense rain band of a hurricane.

Storm Surge

Local sea level rise due to storm winds.

Wind Speed

Measured in kmph; affects storm surge height.

Heavy Rains

Can cause extensive flooding during cyclones.

Cyclogenesis

Formation of cyclones from frontal systems.

Geographic Regions at Risk

Areas prone to tropical and extratropical cyclones.

High Winds

Destructive winds, can exceed 320 kmph.

Natural Service Functions

Cyclones provide precipitation and ecosystem benefits.

Forecasting Tools

Includes satellites, radar, and reconnaissance aircraft.

Hurricane Watch

Issued when storm likely to impact in 36 hours.

Hurricane Warning

Issued when storm likely to impact in 24 hours.

Doppler Radar

Measures rainfall, wind speed, and storm direction.

Computer Models

Predict hurricane changes using available data.

Storm Surge Predictions

Estimates of sea level rise during storms.

Historic High Winds Events

Notable hurricanes with extreme wind speeds.

Conditions for Upgrade

Factors for tropical disturbance to become a hurricane.

Easterly Waves

Weather patterns forming over western Africa.

Coastal Erosion

Increased by cyclonic storms impacting shorelines.

Anthropogenic Climate Change

Influences intensity and frequency of hurricanes.

Evacuation Plans

Strategies to move populations from harm's way.

Building Codes

Regulations to minimize cyclone damage.

Rainfall Impact

Factors influencing inland flooding during storms.

Trough

Elongated area of low pressure in cyclones.

Fetch

Area over which wind blows, affecting surge height.

Latent Heat

Energy released during condensation, fueling storms.

Occluded Front

Cold front catches warm front, blocking it.

Wind Shear

Change in wind speed and direction with height.

Coriolis effect

The apparent deflection that occurs as a result of the rotation of a body (earth); deflection to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

Cyclone Classification

All cyclones can be classified by their intensity based on max sustained wind speed (1 minute).

Warm Ocean Waters

Warm ocean waters release latent heat during condensation, fueling storms.

Mature Structure

A hurricane has a diameter of 500 km (~310 mi.), with max wind speeds over 119 kmph (~74 mph) limited to the interior of the storm.

Linkages with other Natural Hazards

Massive cyclonic storms are closely linked to other hazards such as coastal erosion, saltwater flooding, and landslides.

Human Interactions with Cyclones

Increase population and population density in coastal cities at risk of tropical cyclones; 53% of U.S. lives in coastal counties.

Minimizing the Effects of Cyclones

Focus on ways to reduce property damage and avoid loss of life through accurate forecasting and timely advisories.

Perceptions of Cyclones

Despite the threat of heavy losses, many don't take watches, warnings, and evacuations seriously.

Effects of Cyclones

Damage caused by both types of cyclones is enormous, including flooding, thunderstorms, tornadoes, snowstorms, and blizzards.

Historic High Winds Events of Note

Hurricanes with gusts over 320 kmph include Andrew (1992), Camille (1969), and Labor Day Hurricane (1935).

Factors Affecting Inland Flooding

Include storm's speed, changes in land elevation, interactions with other storms, and drainage patterns.