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Hurricanes

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... scale (1-5) that describes the damage potential of a hurricane. ... Hurricane Andrew -- August 24, 1992. 42. Aircraft Detection of Hurricanes. WP-3 Aircraft ... – PowerPoint PPT presentation

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Title: Hurricanes


1
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

2
Hurricanes
  • To begin our study of hurricanes we must first
    look at the typical weather in the tropics.
  • The sun typically remains high in the sky all
    year -- little variation in temperature with
    seasons.
  • The strong sun heats the water and enhances the
    evaporation of the water.
  • The general flow of air near the equator is out
    of the east -- Trade Winds.

3
General Circulation
4
Hurricanes
  • The trade winds blow from the northeast in the
    Northern Hemisphere and from the southeast in the
    Southern Hemisphere.
  • A region of convergence (Intertropical
    Convergence Zone -- ITCZ) creates a band of
    thunderstorms near the equator.

5
General Circulation
6
Hurricanes
  • 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.

7
Tropical Wave in the Easterlies
8
Conditions for Tropical Wave Development
  • The wave must be north or south of the equator.
  • Coriolis force is zero at the equator.
  • Conditional Instability
  • Weak vertical shear
  • This is different from what we want in the
    mid-latitudes.
  • Warm sea-surface temperatures (SST)
  • Typically SSTs are greater than 26oC

9
Hurricane Development
  • Convergence at the surface leads to convergence
    of moisture.
  • The convection or thunderstorms that form release
    latent heat which intensifies the surface low.
  • The warm core column of air will create an upper
    level high pressure center.
  • The weak shear allows the storm to remain
    vertical and allows for the latent heat release
    to enhance the surface low.

10
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
11
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
12
Hurricane Structure
This feedback mechanism continues as long as the
favorable conditions for hurricane growth
continue to exist.
13
Hurricane Development
  • This feedback mechanism is called CISK
  • Conditional Instability of the Second Kind
  • 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
    the strongest storms, keeps the eye cloud-free.

14
Eye of the Storm
15
Birthplaces of Hurricanes
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.
16
Tropical Wave 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.

17
Tropical Wave 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.

18
Tropical Wave 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.

19
Tropical Wave Development
20
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 grow in the larger Pacific
    ocean.
  • Wind damage can be significant especially to
    weakly built houses.
  • Spin-up vortices can cause very strong and
    damaging wind gusts.

21
Hurricane Winds
22
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
23
Hurricane Wind Damage
24
Hurricane Hazards
  • Inland Flooding
  • Torrential rains can, especially if the hurricane
    moves slowly inland, can cause substantial
    flooding.
  • Camille (1969)
  • Inland in Mississippi
  • Flooding in Virginia
  • Agnes (1972)
  • Inland in Florida
  • 6.3 Billion in damage along the East Coast
  • Flooding in Pennsylvania
  • Alberto (1994)
  • Never a hurricane! (Tropical Storm)
  • Stalled over Georgia -- Americus, GA received 21

25
Flooding in Richmond, VA
Hurricane Camille -- 19 August 1969
26
Flooding in Wilkes-Barre, PA
Hurricane Agnes -- 19-20 June 1972
27
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).

28
Storm Surge
29
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

30
Before the Hurricane
Richelieu Apartments -- Pass Christian,
MS Hurricane Camille -- 17 Aug 1969
31
After the Hurricane
32
Camille Storm Surge
Pass Christian, MS Storm Surge 7.4 m Hurricane
Camille -- 17 Aug 1969
33
Before Hugo
Folly Beach, SC -- 22 September 1989
34
After Hugo
Folly Beach, SC -- 22 September 1989
35
Death of a Hurricane
  • Moves out of the warm, moist tropical air.
  • Moves over land.
  • Loss of moisture source
  • Increased surface friction
  • Temperature of the land is cooler than the warm
    ocean
  • Moved under unfavorable large scale flow.
  • High shear can rip a storm apart
  • Large scale subsidence can inhibit convection

36
Hurricane Warnings
  • Hurricane warnings are designed to protect human
    life and their property.
  • Possible Evacuations
  • Detection techniques
  • Satellites
  • Radar
  • Aircraft Reconnaissance
  • Data Buoys
  • Weather Channel Reporters!

37
Satellite Detection of Camille
NIMBUS III Satellite -- 21 August 1969
38
Satellite Tracking of Allen
Hurricane Allen -- August 1980
39
Satellite Tracking of Allen
Hurricane Allen -- August 1980
40
Satellite Tracking of Allen
Hurricane Allen -- August 1980
41
Radar Detection of Hurricanes
Hurricane Andrew -- August 24, 1992
42
Aircraft Detection of Hurricanes
WP-3 Aircraft
Dropsondes
43
Tropical Storm Warnings
  • Tropical Storm Watch
  • Possible tropical storm conditions expected in
    the next 36 hours.
  • Prepare to take appropriate action.
  • Tropical Storm Warning
  • Tropical storm conditions are expected in the
    next 24 hours.
  • Take action!

44
Hurricane Warnings
  • Hurricane Watch
  • Possible hurricane conditions expected in the
    next 36 hours.
  • Prepare to take appropriate action.
  • Hurricane Warning
  • Hurricane conditions are expected in the next 24
    hours.
  • Get out of Dodge!

45
Hurricane Warning!
46
Building for Disaster?
  • 45 million people now live along hurricane-prone
    regions in the U.S.
  • Gulf Coast population
  • 1960 -- 5.2 Million
  • 1990 -- 10.1 Million
  • Doubled in only 30 years.
  • Florida to Virginia
  • 1960 -- 4.4 Million
  • 1990 -- 9.2 Million

47
Can We Evacuate?
  • Hurricane evacuation times currently range from
    15 - 30 hours depending on the locale.
  • Current warnings are only valid for 24 hours.
  • Can the transportation infrastructure handle such
    a mass exodus quickly enough?

48
Building for Disaster?
  • We are constructing more and larger dwellings
    along our hurricane-prone coastlines.

49
Building for Disaster?
Miami, FL
50
Better Construction
  • Improved construction techniques may help
    alleviate some storm damage.
  • Reinforcing seawalls
  • Creating larger sand dunes and beaches
  • Building housing on stilts
  • Better tie-downs between the foundation and the
    walls and between the walls and the roof.
  • Not much will stop a 7 m storm surge.

51
Is This Better?
52
Prediction Difficulty
  • We still have difficulty predicting the precise
    landfall of most hurricanes.
  • Some hurricanes can loop.
  • What if we evacuate and the hurricane goes
    elsewhere -- the Cry Wolf problem.
  • False alarms are still high and many people
    become apathetic.
  • We see that here with tornado watches and
    warnings!

53
Prediction Difficulty
Hurricane Elena -- 28 August - 4 September 1985
54
Possible Solutions
  • Increased Research on Hurricane Prediction
  • Evacuation Studies
  • Emergency procedures in the event evacuation is
    not feasible
  • Population growth management
  • Hurricane education
  • Improved construction building codes
  • Wetland management
  • Hurricane Modification ????
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