Topic 13Hurricanes

GEOL 2503

Introduction to Oceanography

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Garden City, South Carolina after Hurricane Hugo (1989)3

North coast of Puerto Rico after Hurricane Hugo (1989)4

US Hurricanes

• Galveston 1900 deadliest–6000 dead

• Strongest hurricanes-1935 Florida Keys-1969 Camille (Gulf coast, MS)

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Deadliest (Deaths)

1900 Galveston (8000)

1928 SE Florida (2500)

2005 Katrina (1500)

1893 LA (1100-1400)

1893 SC/GA Sea Islands (1000-2000)

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Years of maximum and minimum tropical storm, hurricane, and major hurricane activity in the Atlantic basin 1851-2006.

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Years of maximum United States hurricane and major hurricane strikes 1851-2006

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Hurricanes

• Rotating air• Winds exceed 64 knots (74 mi/hr) • Rotate counter-clockwise in the Northern

Hemisphere (clockwise in the Southern Hemisphere).

• Visit the National Hurricane Center web page at http://www.nhc.noaa.gov/

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What is a cyclone?

• In meteorology, a cyclone refers to an area of closed, circular fluid motion rotating in the same direction as the Earth

• Usually characterized by inward spiraling winds

• Rotate counter clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere of the Earth.

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Cyclones

• Tropical cyclones—generated in the tropics

• Extratropical cyclones—generated outside of the tropics

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Hurricane Formation

• Formed from thunderstorms • Ocean water itself must be warmer than

26.5 degrees Celsius (81°F)• Hurricanes weaken rapidly when they travel

over land or colder ocean waters

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ITCZ—birthplace of hurricanes

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Summer Sea Surface Temperatures

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Why no hurricanes here?

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Tropical cyclones

• Tropical depression– Winds less than 38 mph

• Tropical storm– Winds 39-73 mph

• Hurricane– Winds 74 + mph

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The warm water is one of the most important keys as it is water that powers the tropical cyclone. As water vapor rises, it cools. This cooling causes the water vapor to condense into a liquid we see as clouds. Condensation releases heat, which warms the atmosphere, making the air lighter still which then continues to rise into the atmosphere. As it does, more air moves in near the surface to take its place which is the strong wind we feel from these storms.

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The main parts of a tropical cyclone are the rainbands, the eye, and the eyewall. Air spirals in toward the center in a counter-clockwise pattern in the northern hemisphere (clockwise in the southern hemisphere), and out the top in the opposite direction. In the very center of the storm, air sinks, forming an "eye" that is mostly cloud-free. 19

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Given that sea surface temperatures need to be at least 80°F (27°C) for tropical cyclones form, it is natural that they form near the equator. However, with only the rarest of occasions, these storms do not form within 5° latitude of the equator. This is due to the lack of sufficient Coriolis Force.

Typhoon

Cyclone

HurricaneHurricane

Cyclone

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Progression of Tropical Systems

Classic “Cape Verde” hurricane track

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Tropical Disturbance

• A discrete tropical weather system of apparently organized convection originating in the tropics or subtropics, maintaining its identity for 24 hours or more.

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Tropical Depression

• A tropical cyclone in which the maximum sustained wind speed is 33 kt (38 mph, 17 m/s).

• Depressions have a closed circulation.

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Tropical Storm

• A tropical cyclone in which the maximum sustained surface wind speed ranges from 34 kt (39 mph,17.5 m/s) to 63 kt (73 mph, 32.5 m/s).

• The convection in tropical storms is usually more concentrated near the center with outer rainfall organizing into distinct bands.

• Tropical storms receive a name

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Hurricanes

• A tropical cyclone with winds equal to or exceeding 64 kt (74 mph, 33 m/s)

• Hurricanes are further designated by categories on the Saffir-Simpson scale.

• Hurricanes in categories 3, 4, 5 are known as Major Hurricanes or Intense Hurricanes.

• Known as typhoons or cyclones in some ocean basins

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The Saffir-Simpson Scale

Category 1 2 3 4 5

Pressure (mb) >979 979-965 964-945 944-920 <920

Wind (mph) 74-95 96-110 111-130 131-154 >154

Storm surge (ft) 4-5 6-8 9-12 13-18 >18

Damage Minimal Moderate Extensive Extreme Catastrophic

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Tracks of systems that became major hurricanes after forming in Tropical Atlantic or Caribbean Sea

Active 24-Year Period 1955-1970, 1995-2002

67 Major Hurricanes

Inactive 24-Year Period 1971-1994

27 Major Hurricanes29

Storm Surge

• Local rise in sea level caused by storm processes – Wind– Waves– Low air pressure

• Not “STORM TIDE”

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Normal high tide here is 2 feet above sea level.The storm surge is an additional 15 feet.Giving a total water level of 17 feet.

High water level (+17 feet)

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stor

m s

urge

high water level

tide level

Observed (high water level) - Predicted (tides) = Storm Surge

Storm-surge levels along South Carolina coast (from FEMA). 32

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What would the wind history be at cities A, B, and C as the hurricane makes landfall?34

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Photo courtesy of the National Climate Data Center

Floyd vs Andrew

Andrew was much stronger, but Floyd was much larger36

Lake PontchartrainNew Orleans

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Katrina pushed water into Lake Pontchartrain

Water broke through flood

walls into N

ew O

rleans

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Which one is not an idiot?

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B(4) warm water vapor

C(1) cool dry air

A(2) eye of the hurricane

D(3) spiral rain bands

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GPS Dropsondes

• Deployed from aircraft to measure temperature, humidity, pressure, and winds between flight level and the surface

• As the sonde falls at 10 m/s (2000 ft/min) it is also pushed by the wind

• The wind can be determined from the Doppler shifts of the GPS signals.

• Readings are relayed to the airplane at half second intervals.

• Vertical resolution for all measurements is 5 m

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Dropsondes

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3 major hurricanes struckGA coast in the 1890’s

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Landfall near Brunswick as a Cat. 4 with max winds of 135 mph

180 dead; $56.5 million in damage (2004 dollars)

Max storm surge was 13-18 ft. in Darien

http://www.srh.noaa.gov/jax/research/hurricanes/history/1898/

Oct 1898 – Georgia Hurricane

3 major landfalls in the 1890’s (but none since 1900)

Potential for big storm surge owing to shallow shelf

Barrier islands at extra risk associated with sea level rise

Risks to Coastal Georgia

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Impacts of floods

Hurricane Frances (2004) caused $41M damageto Atlanta from flooding

Immediate impacts: property damage, injuries, death

Health issues: infectious diseases, exposure to toxins

Key water quality issues:

• Floodwater tainted with raw sewage, pesticides, agricultural waste, petroleum products, dead animals

• Flooding of animal waste retention pools from hog, cattle, dairy, poultry farms

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Case Study: Hurricane Ivan (2004) Category 3 hurricane that made landfall just west of Gulf Shores, AL

Produced 25 tornadoes in GA resulting in 2 deaths and 10 injuries.

Rainfall in excess of 5 to 10 in. and high winds destroyed 50% pecan and 15% cotton crop in GA.

Property damage in GA $68.8 M.

From National Climatic Data Center Satellite Archives

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While no major hurricane strikes since 1900, increases in # of Atlantic storms increases the probability of a GA landfall

Landfall on GA coast has potential for big storm surge owing to shallow shelf

Barrier islands at extra risk associated with sea level rise

Heavy rainfall associated with storms that make landfall in the Gulf; rainfall in hurricanes is expected to increase

Tornadoes likely to be spawned in GA by increasingly intense storms that make landfall in the Gulf

Hurricane Risks to Georgia

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Coastal ecosystems will eventually adapt, but hurricanes will cause short term damage to maritime forests, wetlandsmarshes, and wildlife disruptions

Human systems will face shoreline erosion, loss of beachesand dunes, damage to structures, economic losses. Adaptation strategies include:Land useCoastal engineeringBuilding codesWetlands preservationForest preservation

Adaptation Strategies

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Hurricane Tracking and Forecasting

• Track forecast cone, 3-day and 5-day• Watches and warnings• Wind speed probabilities• Surface wind field (measured)• Storm surge probabilities

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Tropical Cyclone Track Forecast Cone and Watches/Warnings

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