WHAT YOU NEED TO KNOW ABOUT HURRICANES & TROPICAL

CYCLONES

WHAT YOU NEED TO KNOW ABOUT HURRICANES & TROPICAL

CYCLONES

AUG 19, 2009

TROPICAL CYCLONES

Marvin Bennett and Ken Tobin

(CEES/TAMIU)

OVERVIEW

DEFINITIONS, CLIMATOLOGY, & HISTORY

HURRICANE HAZARDS

FORECAST PROCESS

HURRICANE PREPAREDNESS

Tropical Cyclone Definitions

Tropical Cyclone is a generic term for a warm-core low pressure system that forms in the tropics or subtropics.

Tropical Systems are further categorized by a difference in their wind speed.

Tropical Cyclogenesis (Formation)

Tropical Disturbance with thunderstorms

Distance of at least 300 miles from the equator

Ocean temperatures at 80ºF or warmer

Abundant moisture - low and middle part of atmosphere

Weak vertical wind shear

To become a tropical cyclone several ingredients are needed:

TROPICAL CYCLONESBIRTH : Nearly all tropical storms/hurricanes start out as a tropical disturbance - an area of unsettled weather in the tropics.

Tropical Storm Cyclogenesis (Formation)

The conditions on the previous slide only occur close to the tropics (generally within 25o latitude) & during specific times of year!

Hence hurricane season in the Atlantic Basin is defined between June 1 and November 30.

The peak in hurricane season is around September 10th, which corresponds to the time when ocean water in the tropics reaches its maximum temperature.

Tropical Cyclone Definitions

Tropical Depression = < 39 mph

Tropical Storm = 39 mph – 73 mph

Hurricane = > 74 mph

Major Hurricane = > 110 mph (Cat 3 or greater)

Once a distributed area becomes organized this system becomes a Tropical Cyclone.

Tropical Cyclones are categorized by difference in their wind speed:

Tropical Cyclone EvolutionTropical Depression = < 39 mph

Tropical Cyclone Evolution

Tropical Storm = 39 mph - 74 mph

Tropical Cyclone EvolutionHurricane = > 74 mph

Hurricane Isabel’s power initially focused attention on the storm, but its size, not power, ensured it would be destructive.   Surfers loved the big waves rolling into Ocean City, N.J., on Monday, but when Isabel hit on Thursday, much larger waves were hitting much of the East Coast.  

Tropical Cyclone Structure• Doppler radar showing

hurricane main parts:

– Eye

– Eyewall

– Rainbands.

• Counter-clockwise rotation.

• In very center of the storm, air sinks, forming an "eye" that is mostly cloud-free.

FAMILY OF TROPICAL CYCLONES

INFRARED SATELLITE PHOTOGRAPH … AUGUST 28, 1996

Tropical Climatology

• Storms favor the Gulf of Mexico & Western Caribbean

Points of Origin -- June

Tropical Climatology

• Most active month of the hurricane season.

Points of Origin -- September

Texas Hurricanes - Galveston

• Sep 8-9, 1900• 8000+ killed• $30M damage• 20 ft. surge• Max 135 mph• Cat 4

LOUISIANA

MEXICO

TEXAS

* Galveston

Points of Origin -- September

Tropical Cyclone Hazards

• Storm Surge

• High Winds

• Inland Flooding

• Tornados

Tropical Storm/ Hurricane Impacts

• Storm Surge - simply water that is pushed toward the shore by the force of the winds swirling around the storm.

• Advancing surge combines with normal tides to create the hurricane storm tide - can increase the average water level 15 feet or more.

Tropical Cyclone ImpactsCameron County

Storm SurgeFrom SLOSHModel

Tropical Storm/ Hurricane Impacts

Heavy rains create inland flooding that results in fatalities and/or loss of property. An example is Hurricane Carla where in Jefferson County, 180 miles from the land falling storm, $17.5 million in damage occurred, with $14 million of it water damage. Rain totaled up to 19". Three to four feet of water flooded Port Arthur. Total damages from Carla estimated near $400 million.

Tropical Storm/ Hurricane Impacts• Tornadoes

– Hurricane Carla had its greatest impact in Texas.

– Twenty-six tornadoes were spawned

– one tore apart 120 buildings and killed 6 in Galveston

Hurricane Beulah spawned over 100 tornadoes

Forecast Process

• Forecasts obtained by either postal zip code, city/state search, or by point & click maps

• Weather Information in clear, concise format

• Emphasizes local weather expertise

NWS Internet Site www.srh.noaa.gov

Forecast Process

• TROPICAL STORM WATCH - A tropical storm watch is issued when tropical storm conditions, including winds from 39 to 73 miles per hour (mph), pose a possible threat to a specified coastal area within 36 hours.

• TROPICAL STORM WARNING - A tropical storm warning is issued when tropical storm conditions, including winds from 39 to 73 mph, are expected in a specified coastal area within 24 hours or less.

Forecast Process

• HURRICANE WATCH - A hurricane watch is issued for a specified coastal area for which a hurricane or a hurricane-related hazard is a possible threat within 36 hours.

• HURRICANE WARNING - A hurricane warning is issued when a hurricane with sustained winds of 74 mph or higher is expected in a specified coastal area in 24 hours or less. A hurricane warning can remain in effect when dangerously high water or a combination of dangerously high water and exceptionally high waves continues, even though the winds may have subsided below hurricane intensity.

Forecast Process - Graphic ProductNote that thecenter line indicates the “average” of the forecast track.

Storm can endup any where in the cone & affect areas outside of the cone

The size of the coneincreases as the forecast periodbecomes greater

Tropical Cyclone Preparedness

Hypothetical Hurricane “Carly”

Brownsville Landfall Source: UT Space Science Center

Tropical Cyclone Preparedness

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Source: UT Space Science Center

Brownsville / South Padre I.Mean Sea Level

Brownsville

Source: UT Space Science Center

Brownsville

Hurricane Carly9/11 at 1500 CDT

MEOW NW at 8 MPHSurge: 17.3 Feet

Source: UT Space Science Center