WHAT YOU NEED TO KNOW ABOUT HURRICANES & TROPICAL CYCLONES

AUG 19, 2009

TROPICAL CYCLONES Marvin Bennett and Ken Tobin (CEES/TAMIU)

OVERVIEW

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DEFINITIONS, CLIMATOLOGY, & HISTORY

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HURRICANE HAZARDS

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FORECAST PROCESS

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HURRICANE PREPAREDNESS & RESPONSE

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

Tropical Cyclones are further categorized by the difference in their wind speeds.

Tropical Cyclogenesis (Formation)

To become a tropical cyclone several ingredients are needed:     

Tropical Disturbance with thunderstorms Distance of at least 300 miles from the equator Ocean temperatures at 80 ºF or warmer Abundant moisture - low and middle part of atmosphere Weak vertical wind shear

TROPICAL CYCLONES

BIRTH : 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 25 o 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

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

Remember that Tropical Cyclones are categorized by differences in their wind speeds:     Tropical Depression = < 39 mph Tropical Storm = 39 mph – 74 mph Hurricane = > 74 mph Major Hurricane = > 110 mph (Cat 3 or greater)

Tropical Cyclone Evolution Tropical Depression = < 39 mph

Tropical Cyclone Evolution Tropical Storm = 39 mph - 74 mph

Tropical Cyclone Evolution Hurricane = > 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: – Rainbands – Eye – Eyewall.

• 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

Points of Origin -- June

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Storms favor the Gulf of Mexico & Western Caribbean

Tropical Climatology

Points of Origin -- July

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Continued Gulf activity, increasing danger - Greater Antilles

Tropical Climatology

Points of Origin -- August

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Atlantic more active, long-track hurricane danger increases.

Tropical Climatology

Points of Origin -- September

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Most active month of the hurricane season.

Tropical Climatology

Points of Origin - October

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Caribbean and Western Atlantic is most active.

Tropical Climatology

Points of Origin -- November

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Caribbean & Western Atlantic most active. Elsewhere, storms can be strong, although conditions are less favorable.

Texas Hurricanes - Galveston LOUISIANA

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Sep 8-9, 1900 8000+ killed $30M damage 20’ surge Max 135 mph Cat 4 TEXAS * Galveston Points of Origin -- September MEXICO

Texas Hurricanes - Beulah

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Sep 20-21, 1967

LOUISIANA

TEXAS

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10 killed

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$200M damage

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Cat 4 (landfall)

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Max 165 mph MEXICO *Brownsville

Texas Tropical Storm Allison

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Jun 5-10, 2001

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41 killed

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$5.0B damage

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Max 60 mph TEXAS LOUISIANA *Houston MEXICO

Texas Hurricane Dolly

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July 22-24, 2008 TEXAS

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1 killed

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$+1.0B damage

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Max 100 mph Tropical Storm MEXICO LOUISIANA *Houston Hurricane Tropical Storm

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.

STORM SURGE

Tropical Cyclone Impacts Cameron County Storm Surge From SLOSH Model

Tropical Cyclone Impacts Cameron County Storm Surge From HAZUS Model

Tropical Storm/ Hurricane Impacts

Heavy rains create million.

inland flooding

that results in fatalities and/or loss of property. An example is Hurricane Carla

where i

n Jefferson County, 180 miles from the land falling storm, $17.5 million in damage occurred, with $14 million of it water damage. Rain totaled 19" at Votan. Three to four feet of water flooded Port Arthur. Total damages from Carla estimated near $400

Tropical Cyclone Impacts Cameron County 100 Year FEMA Floodplains (Zone A)

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

Tropical Cyclone Impacts Cameron County Tornados Since 1950 From NCDC

Forecast Process NWS Internet Site

www.srh.noaa.gov

• 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

Forecast Process

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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.

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TROPICAL STORM WARNING -

24 hours or less.

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

Forecast Process

•

HURRICANE WATCH -

within 36 hours.

A hurricane watch is issued for a specified coastal area for which a hurricane or a hurricane-related hazard is a possible threat •

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 Product

Note that the center line indicates the “average” of the forecast track.

Storm can end up any where in the cone & affect areas outside of the cone The size of the cone increases as the forecast period becomes greater

Tropical Cyclone Preparedness

• While official watches and warnings are issued on a time frame of 24 or 36 hrs EM professional need much more lead time to prepare.

• H Hour: The time in hours before Tropical Storm Force winds touch the coast.

• For Atlantic storms the countdown starts at H-120 • Storms that form off the coast of Texas can have as little as 24 hours from the formation to landfall.

Tropical Cyclone Preparedness Considerations

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When to Evacuate.

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How to Go.

Why Go?

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Where to Go.

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Sheltering.

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When is it Safe to Return ?

Tropical Cyclone Preparedness When to Evacuate?

• H-72 The timeframe on Atlantic formed storms when the County Judge will make the decision to implement the Special Need Evacuation process. Bus loading will start at H-60 closest to 6 a.m.

• H-48 to H-36 Mandatory Evacuation orders for All Coastal Zip Zones in for a Catastrophic Hurricane Approaching the coast

Tropical Cyclone Preparedness - How to Go?

Tropical Cyclone Preparedness Why go?

Hypothetical Hurricane “Carly” Brownsville Landfall

Source: UT Space Science Center

Tropical Cyclone Preparedness Why go?

.

Source: UT Space Science Center

Brownsville Brownsville / South Padre I.

Mean Sea Level

Source: UT Space Science Center

Brownsville Hurricane Carly 9/11 at 1500 CDT MEOW NW at 8 MPH Surge: 17.3 Feet

Source: UT Space Science Center

Tropical Cyclone Preparedness When to Return?

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Contact your Local Emergency Management Agency for information

.