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 Pressure (mb)
Winds (mph)
1: Mild >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_Katrina_SSHeights.jpg
Hurricane Structure
Hurricane Structure: 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
The calm, circular center of a hurricane. Winds blow in a counterclockwise spiral around 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 counter-clockwise 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
Projected path Actual path
Tracking Hurricanes
Hurricane PathsThe 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.
GULF OF MEXICO
AUG. 25TH, 2005 12:30 PM
AUG. 24TH, 2005 11:50 AM
AUG. 27TH, 2005 10:42 AM AUG. 28TH, 2005 8:42 AM
AUG. 29TH, 2005 8:20 AM
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
DepressionTropical Storm
Category 1Category 2Category 3Category 4Category 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
DepressionTropical Storm
Category 1Category 2Category 3Category 4Category 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.
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