Transcript Hurricane Katrina

Hurricane Katrina
Presented by:
Meredith Aronson, Tyler Evans, Margaret Hunziker,
Karyn King and Rachel Frenkil
What Is A Hurricane?
 A hurricane is a strong tropical cyclone over the
Atlantic or Eastern Pacific Oceans in which
sustained winds speeds reach 64 knots.
 Western Pacific: typhoons
 Indian Ocean: cyclones
Classification of Tropical
Weather Systems
-Organized thunderstorm cluster,
no closed circulation.
-Identifiable pressure drop.
Tropical disturbance
Winds < 34 kts (39 MPH)
Tropical depression
34kts < wind < 64 kts (74MPH)
Tropical storm
64kts (74 MPH) < wind
Hurricane
Saffir Simpson Intensity
Scale
Rating
1: Mild
Pressure Winds
(mb)
(mph)
>980
74 - 95
2: Moderate
965-979
96-110
3: Extensive
945-964
111-130
4: Extreme
920-944
131-155
5:
Catastrophic
< 920
>155
Trigger Mechanisms for
Thunderstorms: Hadley Cells
Intertropical Convergence Zone
Trigger Mechanisms for
Thunderstorms: Easterly
Winds/ Mid-latitude Origin
Surface Conditions

Ocean water must be warmer
than 26.5 degrees C (81°F) and
the warm layer has to be at
least 60 m (200ft) deep.

Heat and moisture from warm
water is source of energy for
hurricanes.

Hurricanes weaken rapidly
over land or colder ocean
waters.

Strong surface winds
http://www.osdpd.noaa.gov/PSB/EPS/SST/data/global100.c.gif
Surface Conditions During Hurricane
Katrina

Average Sea surface
temperature in the Gulf Coast
exceeded 30°C.

Wind gusts in MS and LA
exceeded 120 mph.

At its peak, the storm’s sea
level pressure was 902 mb.

To put this into
perspective, the lowest
surface pressure ever
recorded is 870 mb
http://www.nasa.gov/centers/goddard/images/content/148071main_Katri
a_SSHeights.jpg
Hurricane Structure
Hurricane Structure: Eye
The calm, circular center of a
hurricane. Winds blow in a
counterclockwise spiral around the eye.
 About 20-40 miles wide
 Relatively calm
 Little to no rain
 Often has low-level clouds
called “scud clouds”
 Warmest part of the storm
(due to the descending air)
 Strongest winds are to the
right of the eye
Hurricane Structure: Eye
Wall
• A wall of
thunderstorms
surrounding the
eye
• Strongest winds
and most rain
• Changes in
structure of eye
and eyewall
influence the
storm’s severity
Hurricane Structure: Spiral
Rainbands
• Long bands of
rainclouds that appear
to spiral inward
toward the eye
• Outer rainbands can
extend hundreds of
miles from center
• Can be obscured by
higher level clouds,
making it difficult for
forecasters to monitor
the storm
Hurricane Structure: How a
Hurricane Travels
 Rotates
counterclockwise at
wind speeds of
at least 74 mph
 Travels across
land at a
slower pace,
10-25 mph
Development of a Hurricane:
Necessary Upper-Level
Conditions • 5 degrees north of
equator so Coriolis
force can be stronger
• Weak vertical wind
shear
• If warm air is
displaced, no eye
• Hurricanes’
energy and latent
heat
• Low vertical
wind shear
allows for
thunderstorms to
develop
Air Flow in a Hurricane
Air in the Lower Levels
 Surface winds move
heat and moisture
from the ocean to
the atmosphere
 Air above the
surface is
destabilized and
develops into
thunderstorms
 Strong surface
winds maintain this
process throughout
the storm
Air in Upper Levels: the
Eye


Air descends within
the eye from the
stratosphere to 1.5-2
km above the surface

Air within eye is
warmer

Hurricanes are
often called
“warm core
systems”
Boundary of eye (dry
air) & eye wall
(cloudy air) 
evaporative cooling,
air descends more
rapidly
Air in Upper Levels: Eye
Wall
Air ascends

from surface to
tropopause
 Enters eye
wall at base
and spirals
inward
toward the
eye
 Small
amounts
enter from
the eye
The path of a hurricane depends on the area that it originates in.
Hurricanes are greatly affected by the global wind pattern, the
global wind pattern is broken up into three wind belts in each
hemisphere.
WIND BELTS:
Polar Easterlies
Prevailing Westerlies
Tropical Easterlies
A hurricane originating in the eastern tropical Atlantic is driven
westward by easterly trade winds from the tropics. These storms turn
northwestward around subtropical high and move into higher
latitudes. For this reason, the Gulf of Mexico and the East Coast of
the United States have higher chances of experiencing hurricanes each
year.
AUG. 24TH, 2005 11:50 AM
AUG. 25TH, 2005 12:30 PM
Date
UTC
Wind
Speed
(kts)
Pressure
(mb)
8/23
18 Z
30
1008.0
8/24
00 Z
30
1007.0
8/24
06 Z
30
1007.0
8/24
12 Z
35
1006.0
8/24
18 Z
40
1003.0
8/25
00 Z
45
1000.0
8/25
06 Z
50
997.0
8/25
12 Z
55
994
8/25
18 Z
60
988
8/26
00 Z
70
983
8/26
06 Z
65
987
8/26
12 Z
75
979
8/26
18 Z
85
968
8/27
00 Z
90
959
8/27
06 Z
95
950
8/27
12 Z
100
942
KEY:
Tropical Depression
Tropical Storm
Category 1
Category 2
Category 3
Category 4
Category 5
Date
UTC
Wind
Speed
(kts)
Pressure
(mb)
8/27
18 Z
100
948
2/28
00 Z
100
941
8/28
06 Z
125
930
8/28
12 Z
145
909
8/28
18 Z
150
902
8/29
00 Z
140
905
8/29
06 Z
125
913
8/29
12 Z
110
923
8/29
18 Z
80
948
8/30
00 Z
50
961
8/30
06 Z
40
978
8/30
12 Z
30
985
8/30
18 Z
30
990
8/31
00 Z
30
994
8/31
06 Z
25
996
KEY:
Tropical Depression
Tropical Storm
Category 1
Category 2
Category 3
Category 4
Category 5
Storm Surge
 Abnormal rise in sea level
offshore when a hurricane
approaches the shore
 Low pressure and persistent
wind
 Most powerful over shallow
areas of water, near the
coast or in bays and inlets
 Occurs in front right
quadrant of cyclone
 Most destructive at high
tide

Mechanics of Storm
Surge
Wind
 Ekman Spiral
 Pressure
 In the eye of the
hurricane
 Waves
 Transport water near
the shore
Mechanics of Storm
Surge
 Rainfall
 Additional water in
estuaries
 Earth’s Rotation
 Coriolis Effect
Forecasting Storm Surge
 SLOSH (Sea, Lake, and
Overland Surges from
Hurricanes): model
used to simulate surges
from hurricanes.
 Uses pressure, size,
motion, track and
winds to forecast surges
 Accurate to within 20%
Measuring Storm Surge
 Measure the difference
between the forecasted
tide and the amount of
risen water observed
 Pressure transducers
along the coastline
record the height of
water overhead if
submerged
 Tidal predictions
Storm Surge Reporting
 After a flood, surveyors
map out High Water
Marks (HWM) using
photos and written
descriptions.
 If the water height cant be
broken down and the
water from the surge can
be defined, then it is
classified as a storm surge.
 If not, classified as a storm
tide.
Storm Tide
 Water level made higher by a storm surge as well as
the astrological tides.
 Occurs at the zenith of the storm surge
Storm Surge in Hurricane
Katrina
 Flooding from the storm surge caused:
 Beach erosion
 Obliterated the Chandeleur Islands
 Caused 53 levee breaches
 Submerged 80% of the city
Storm Surge Flooding
"I do not think anyone can tell you with confidence right
now whether the levees will be topped or not [by
storm surge] , but that's obviously a very, very great
concern.”
Katrina’s Destruction
 Katrina was not the deadliest hurricane because of
increases in technology and communication.
 The deadliest Atlantic hurricane occurred in 1780.
 However, it was the costliest hurricane in the US since
1900.
 Estimated damage costs for the US was
$81,200,000,000.