WHAT YOU NEED TO KNOW ABOUT HURRICANES

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WHAT YOU NEED TO KNOW ABOUT HURRICANES TROPICAL
CYCLONES
AUG 19, 2009
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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

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

• Tropical Depression lt 39 mph
• Tropical Storm 39 mph 73 mph
• Hurricane gt 74 mph
• Major Hurricane gt 110 mph (Cat 3 or greater)

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Tropical Cyclone Evolution
Tropical Depression lt 39 mph
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Tropical Cyclone Evolution
Tropical Storm 39 mph - 74 mph
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Tropical Cyclone Evolution
Hurricane gt 74 mph
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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.

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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 -- September

• Most active month of the hurricane season.

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Texas Hurricanes - Galveston
LOUISIANA

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

TEXAS
Galveston
MEXICO

Points of Origin -- September
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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 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.

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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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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

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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
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Tropical Cyclone Preparedness
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The End