Meteorology 1014

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Chapter 11 Hurricanes
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Hurricanes

• Hurricanes are large, tropical storm systems that
  form and develop over the warm waters near the
  equator.
• They are responsible for weather that can
  devastate entire communities
• Heavy rain -- Flooding
• Strong Winds
• Very Large Waves and Storm Surge
• Possibly Tornadoes

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Hurricane Elaina
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Typical conditions in the tropics.

• The sun remains high in the sky all year
• Little variation in temperature with season.
• The strong sun heats the water and enhances the
  evaporation.
• The general flow of air near the equator is out
  of the east -- Trade Winds.

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Intertropical Convergence Zone ITCZ

• The trade winds blow from the northeast in the
  Northern Hemisphere and from the southeast in the
  Southern Hemisphere.
• A region of convergence creates a band of
  thunderstorms near the equator.

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General Circulation
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Tropical Wave

• Since pressure gradients are small near the
  equator, we look at the flow of wind to find
  trough regions.
• A trough or ripple in the easterly flow is known
  as a tropical wave.
• Surface convergence occurs on the east side of
  this wave and surface divergence occurs on the
  west side.
• Thunderstorms tend to form on the east side of
  the tropical wave.

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Tropical Wave in the Easterlies
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Conditions for Tropical Wave Development

• The wave must be north or south of the equator.
• Coriolis force is zero at the equator.
• Conditional Instability (humidity)
• Weak vertical shear
• Warm sea-surface temperatures (SST)
• Typically SSTs are about 80oF or higher

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Hurricane Development

• Convergence at the surface leads to uplift and
  thunderstorms.
• The thunderstorms release latent heat which
  intensifies the uplift.
• The weak shear allows the storm to remain
  vertical and allows for the latent heat released
  to enhance the surface low.

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Hurricane Development
H
The energy for the growth of the storm comes
from the ocean (evaporation). Low shear will
keep the heating in the core to remain above the
surface convergence. Strong shear would rip
the storm apart.
Heating
L
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Hurricane Development
H
L
Strong Heating
As the winds increase, the ocean surface becomes
rougher and friction is added to the balance of
forces. This friction enhances
surface convergence.
Strong Convergence
L
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Hurricane Structure
This feedback mechanism continues as long as the
favorable conditions for hurricane growth
continue to exist.
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Wind Speed Increases Toward Eye
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Profile of a Hurricane
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The Eye

• is the central region of the hurricane.
• It is often cloud free and has relatively calm
  winds.
• The eye is associated with subsidence that, in
  strong storms, keeps the eye cloud-free.

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Birthplaces of Hurricanes
Too cold
Too cold
Hurricane birthplaces are near the equator but
between 5-15 degrees latitude away from the
equator. The paths tend to be easterly as
the hurricanes develop and grow.
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Hurricane Seasons
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Hurricane Names
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Tropical Development

• Tropical Disturbance
• A collection of thunderstorms with a slight
  circulation.
• Tropical Depression
• Closed circulation
• Wind speeds between 20-34 knots.
• Tropical Storm
• Closed circulation
• Wind speeds between 35-64 knots.
• The storm is named.

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Tropical Development

• Hurricane
• Closed circulation
• Sustained wind speeds in excess of 64 kts (74
  mph).
• Saffir-Simpson Scale
• A numerical scale (1-5) that describes the damage
  potential of a hurricane.
• A quick and easy description of the strength of a
  hurricane.

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Tropical Wave Development
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Hurricane Path
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Hurricane path
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Hurricane Hazards

• Strong Winds
• Hurricane sustained wind speeds are in excess of
  74 mph.
• Occasionally can get as high as 155 kts.
• Winds are typically stronger in Pacific storms --
  storms have more time to grow in the larger
  Pacific ocean.
• Wind damage can be significant especially to
  weakly built houses.

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Hurricane Winds
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Hurricane Winds

• Hurricane winds are typically the strongest on
  the right side of the storm.
• The forward motion of the storm is added to the
  wind speeds on the right side of the storm to
  enhance the surface winds.

Strongest winds on the right side of the storm.
Weaker winds
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Hurricane Wind Damage
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High winds
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Hurricane Hazards

• Inland Flooding
• As the hurricane moves slowly inland, heavy rains
  can cause substantial flooding.
• Camille (1969)
• Inland Flooding in Virginia and Mississippi
• Agnes (1972)
• Inland flooding in Florida ? Pennsylvania
• 6.3 Billion in damage along the East Coast
• Tropical storm (1994)
• Flooding in Alberto

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Flooding in Richmond, VA
Hurricane Camille -- 19 August 1969
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Flooding in Wilkes-Barre, PA
Hurricane Agnes -- 19-20 June 1972
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Hurricane Mitch - flooding


Hurricane Mitch - Category 5 hurricane and one of
the most destructive ever recorded in the Western
Hemisphere - struck Central America on October
27, 1998. Honduras, Guatemala, El Salvador, and
Nicaragua suffered tremendous damage. In its
wake, Mitch left nearly 10,000 dead, thousands
more missing, and tens of thousands without homes
or possessions. Infrastructure was devastated,
crops and plantations were destroyed, and entire
villages were washed away by torrential rains.
Those rains also caused horrendous mudslides
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Storm Surge

• The abnormal rise in the ocean level associated
  with the hurricane landfall.
• As the hurricane approaches the coast, it
  pushes a large mass of water in front of it.
• When this pile of water reaches the coast, the
  water levels can rise as much as 7 meters (22
  feet).

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Storm Surge
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Storm Surge

• Usually 80 - 160 km wide.
• Not a tidal wave or tsunami.
• The dramatic rise in the sea level can cause
  catastrophic damage.
• The greatest storm surge is associated with
• Stronger hurricanes
• High tide
• Shape of the shore
• Watch video, Storm Surge, and fill out worksheet.

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Before the Hurricane
Richelieu Apartments -- Pass Christian,
MS Hurricane Camille -- 17 Aug 1969
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After the Hurricane
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Camille Storm Surge
Pass Christian, MS Storm Surge 7.4 m Hurricane
Camille -- 17 Aug 1969
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Hurricane Ike - Texas2008
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Satellite view
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Data Buoy
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Hurricane Detection Tracking

• The National Weather Service broadcasts severe
  weather conditions on radio, TV, or NOAA Weather
  Radio. 
• A hurricane WATCH indicates that a hurricane is
  near enough that everybody in the area covered by
  the "Watch" should listen for subsequent
  advisories.  Watches are usually issued 24-36
  hours in advance of anticipated landfall. 
• A hurricane WARNING indicates that a hurricane is
  expected in a specific coastal area in 24 hours
  or less.  If the hurricane's path is unusual or
  erratic, the warnings may be issued only a few
  hours before the beginning of hurricane
  conditions. 

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Property damage vs loss of life
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Hurricane Modification
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Discussion ??