WHAT YOU NEED TO KNOW ABOUT HURRICANES & TROPICAL CYCLONES
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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 & RESPONSE. Tropical Cyclone Definitions.

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TROPICAL CYCLONES

Marvin Bennett and Ken Tobin

(CEES/TAMIU)


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OVERVIEW

  • DEFINITIONS, CLIMATOLOGY, & HISTORY

  • HURRICANE HAZARDS

  • FORECAST PROCESS

  • HURRICANE PREPAREDNESS & RESPONSE


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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.


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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 80ºF or warmer

  • Abundant moisture - low and middle part of atmosphere

  • Weak vertical wind shear


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TROPICAL CYCLONES

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


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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.


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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)


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Tropical Cyclone Evolution

Tropical Depression = < 39 mph


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Tropical Cyclone Evolution

Tropical Storm = 39 mph - 74 mph


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Hurricane Isabel’spower 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 Evolution

Hurricane = > 74 mph


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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.


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FAMILY OF TROPICAL CYCLONES

INFRARED SATELLITE PHOTOGRAPH … AUGUST 28, 1996


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Tropical Climatology

Points of Origin -- June

  • Storms favor the Gulf of Mexico & Western Caribbean


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Tropical Climatology

Points of Origin -- July

  • Continued Gulf activity, increasing danger - Greater Antilles


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Tropical Climatology

Points of Origin -- August

  • Atlantic more active, long-track hurricane danger increases.


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Tropical Climatology

Points of Origin -- September

  • Most active month of the hurricane season.


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Tropical Climatology

Points of Origin --October

  • Caribbean and Western Atlantic is most active.


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Tropical Climatology

Points of Origin -- November

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


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Texas Hurricanes - Galveston

LOUISIANA

TEXAS

  • Sep 8-9, 1900

  • 8000+ killed

  • $30M damage

  • 20’ surge

  • Max 135 mph

  • Cat 4

* Galveston

MEXICO

Points of Origin -- September


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Texas Hurricanes - Beulah

LOUISIANA

TEXAS

  • Sep 20-21, 1967

  • 10 killed

  • $200M damage

  • Cat 4 (landfall)

  • Max 165 mph

*Brownsville

MEXICO


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Texas Tropical Storm Allison

TEXAS

LOUISIANA

  • Jun 5-10, 2001

  • 41 killed

  • $5.0B damage

  • Max 60 mph

*Houston

MEXICO


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Texas Hurricane Dolly

TEXAS

LOUISIANA

  • July 22-24, 2008

  • 1 killed

  • $+1.0B damage

  • Max 100 mph

*Houston

Tropical Storm

Hurricane

Tropical Storm

MEXICO


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Tropical Cyclone Hazards

  • Storm Surge

  • High Winds

  • Inland Flooding

  • Tornados


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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.



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Tropical Cyclone ImpactsCameron County

Storm Surge

From SLOSH

Model


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Tropical Cyclone ImpactsCameron County

Storm Surge

From HAZUS

Model


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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 19" at Votan. Three to four feet of water flooded Port Arthur. Total damages from Carla estimated near $400 million.


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Tropical Cyclone ImpactsCameron County

100 Year FEMA

Floodplains

(Zone A)


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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


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Tropical Cyclone ImpactsCameron County

Tornados

Since 1950

From NCDC


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Forecast Process

NWS Internet Site www.srh.noaa.gov

  • Forecasts obtained by eitherpostal zip code, city/state search, or bypoint & click maps

  • Weather Information in clear, concise format

  • Emphasizes local weather expertise


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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.


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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.


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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


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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.


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Tropical Cyclone Preparedness - Considerations

  • When to Evacuate.

  • How to Go.

  • Why Go?

  • Where to Go.

  • Sheltering.

  • When is it Safe to Return ?


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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





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Tropical Cyclone Preparedness -When to Return?

  • Contact your Local Emergency Management Agency for

    information.