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.