Hurricanes

HurricanesHurricanes

Tropical CyclonesTropical Cyclones These are the greatest storms on Earth and are among

the most destructive of natural disasters.

They are know by several names, depending on where they form. Hurricane

• Used in the Atlantic and eastern and central Pacific and is derived from the Carib Indian word “huracan” for the Carib god of evil.

Typhoon• Used in the western Pacific

Cyclone• Indian Ocean term

Willy Willy• Used in Australia (also “tropical cyclone”)

Naming HurricanesNaming Hurricanes• Starting in 1953Starting in 1953

– NWS started using female names

• Prior to 1953Prior to 1953– Only the most severe hurricanes were given names– They were often named

• For the place they did the most damage . . . – Galveston Hurricane of 1900

• Or the time they hit . . .– Labor Day Hurricane of 1935– Hurricane of 1938 (Also called “The Long Island Express” or the New

England Hurricane of 1938

• Starting in 1979Starting in 1979 – Male and female names were included in lists for the Atlantic

and Gulf of Mexico

Tropical Storm and Hurricane Names for the Atlantic, Tropical Storm and Hurricane Names for the Atlantic, Gulf of Mexico, and Caribbean SeaGulf of Mexico, and Caribbean Sea

Letters Q, U, X, Y, and Z are not used because there are few common names starting with these letters

Six Separate ListsSix Separate Lists

• The names are used over again at the end of each six-year cycle.

• Each calendar year starts with the next list, even if all the names weren't used the previous year.

• One list is repeated every seventh year. – For example, in 2012 the 2006 list will be used again.

• The exception will be if any names have been retired. The names of storms which have been extremely deadly and costly aren't used again.

• The 2012 list will be the list used in 2006

More on Naming HurricanesMore on Naming Hurricanes

• If more than 21 named tropical cyclones If more than 21 named tropical cyclones occur in the Atlantic basin in a seasonoccur in the Atlantic basin in a season– Additional names are taken from the Greek alphabet

(Alpha, Beta, Gamma, Delta, Epsilon, Zeta, etc.)• If a storm forms in the off-seasonIf a storm forms in the off-season

– The name used is based on the calendar year• Retiring NamesRetiring Names

– Whenever a hurricane has had a major impact, any country affected by the storm can request that the name of the hurricane be “retired” by agreement of the World Meteorological Organization (WMO)

– This means it can’t be used for at least 10 years

Tropical Cyclone CharacteristicsTropical Cyclone Characteristics

• Form over tropical oceans between 5o and 20o latitude (except the South Atlantic and eastern south Pacific)

• By international agreement, a storm is classified a hurricane if wind speeds are 74 mph (119 km/hour) and has a rotary circulation.

• Mature hurricanes average about 600 km (372 miles) across but can be up to about 1500 km (930 miles).

• Pressure drops as much as 60 millibars from the outer edge to the center.• Steep pressure gradient generates rapidly spiraling winds which increase as

the center of the storm is approached (due to conservation of angular momentum).

• Duration: A week or more

Cuba

FL

Hurricane FranVisible Image 9/5/96

The Structure of a Hurricane:The Structure of a Hurricane:Convective Rain BandsConvective Rain Bands

Tropical moisture spiraling inward creates rain bands that pinwheel around the storm center

The Structure of a Hurricane: The Structure of a Hurricane: The Eye WallThe Eye Wall

Eye Wall

• As the inward rush of warm, moist surface air reaches the center of the storm it rises in a ring of cumulonimbus towers.• It’s a doughnut shaped wall of intense convective activity.

The Eye WallThe Eye Wall

Katrina Eye Wall - 2005

Hurricane Charley - 2002

Produces the most intense rainfall and greatest wind speeds

The Structure of a Hurricane:The Structure of a Hurricane:OutflowOutflow

Outflow prevents the convergent flow at lower levels from “filling in” the storm.

The Structure of a Hurricane:The Structure of a Hurricane:The EyeThe Eye

• A quasi-circular or quasi-oval region of light winds and skies that are clear to partly cloudy and free of rain. • Caused by descending air that heats by compression, making it the warmest region of the storm.

Average Diameter is

20 to 30 miles (32 to 48 km)

Can you identify when the eye passed?Can you identify when the eye passed?

Wind speeds recorded by a data buoy in the eastern Gulf of Mexico during the passage of Hurricane Kate (1985)

Eye

Hurricane WilmaHurricane WilmaOctober 2005October 2005

The record for the lowest surface air pressure for an Atlantic Hurricane, 882.0 mb, was recorded in the eye on Oct. 18

Eye

Vertical Section and Associated Patterns of Vertical Section and Associated Patterns of Wind, Pressure, and RainWind, Pressure, and Rain

Hurricane Formation and DecayHurricane Formation and Decay

Cooperative Program for Operational Meteorology, Education and Training

Hurricanes are Huge Heat EnginesHurricanes are Huge Heat Engines

• Fueled by latent heat released when huge quantities of heat are released by condensation.

• Released heat warms the air making it buoyant (unstable).– Results in lower surface air pressure– Initiates a rapid inflow of air

• Requires a large quantity of heat to get started.– Develop most often in late summer– Ocean temperatures 27o C (80o F)

Hurricanes Form in the TropicsHurricanes Form in the Tropics

• Often form in the ITCZ.– Few form poleward of 20 degrees

latitude – Water isn’t warm enough

• Not within 5 degrees of the equator– Coriolis force is too weak to initiate

rotary motion

Tropical DisturbancesTropical Disturbances

• Originate in Africa as disorganized arrays of clouds and thunderstorms

• Weak pressure gradient and little or no rotation• Most die out but some will develop rotation

Africa

S. America

Disturbances Can Become Easterly WavesDisturbances Can Become Easterly Waves

• Streamlines (arrows) show low-level airflow.

• East of the axis– Winds turn slightly poleward

and converge forming clouds– Tropical Disturbances are

associated with this side of the wave

• West of the axis– Winds diverge– Clear skies

• Can develop into a tropical depression

Trade Wind InversionsTrade Wind InversionsPrevent Development into a Tropical DepressionPrevent Development into a Tropical Depression

• Subsiding air in a nearby subtropical high• Turbulence near the surface prevents lower level air from sinking

– An inversion develops between the lower zone and the subsiding warmer layers above

• This reduces the ability of the air to rise.

When Conditions Favor Hurricane When Conditions Favor Hurricane Development . . .Development . . .

• No inversion exists and upper-level winds are not too strong

• A Tropical Depression Forms– Pressure drops at center with a steep gradient– Surface winds strengthen and bring in additional

moisture– Condensation releases heat and air rises

• Further adiabatic cooling forms more clouds• Condensation releases more latent heat

– Higher pressure develops aloft resulting in outflow• These processes continue and the storm forms.

Hurricane DecayHurricane Decay

• Hurricanes diminish in intensity whenever – They are deprived of the warm moisture needed for the source of latent

heat by• Moving over land (roughness of surface also rapidly reduces wind speeds)• Moving over cooler ocean water

– Large-scale flow aloft is unfavorable

Hurricane Allen (1980) loses strength as it moves over land.

(1) (2) (3)

Storm Tracks For 2005 - 28 Named Storms!Storm Tracks For 2005 - 28 Named Storms!

• Influenced by– Trade Winds– Prevailing Southwesterlies– Jet Stream– Other Highs and Lows

Hurricane DestructionHurricane Destruction

• Depends on– Strength of the Storm– Size and population density of the area

affected– Nearshore bottom configuration

Wind DamageWind Damage

• The most obvious type of damage• Debris becomes flying missiles• Mobile homes are particularly vulnerable• High rise buildings, especially upper floors, areVulnerable• Tornadoes that are produced by some hurricanes contribute to the storms damage

Hurricane Andrew

Damage to the roof of the Superdomefrom Hurricane Katrina

Hurricane Wilma

Hurricane WindsHurricane Winds

Storm surge will be greatest along thecoastline hit by the right side of the hurricane

Storm SurgeStorm Surge

• The dome of water 65 to 80 km wide that sweeps across the coast near the landfall position of the eye

• The most devastating damage in the coastal zone• Responsible for 90% of hurricane-caused deaths• Cause:

– Strong onshore winds push water towards the shore– Winds also create violent wave activity.– Low pressure on ocean surface is relatively insignificant

Storm Surge of the Galveston Storm Surge of the Galveston Hurricane of 1900Hurricane of 1900

An unexpected Category 4 storm

Galveston SeawallGalveston Seawall

25-Storm Surge From Hurricane Camille (1969)25-Storm Surge From Hurricane Camille (1969)

The Richelieu Apartments in Pass Chistian, MS

Before

After

Katrina Storm Surge and FloodingKatrina Storm Surge and Flooding

Katrina Flooded an Estimated 80% of Katrina Flooded an Estimated 80% of New Orleans in 2005New Orleans in 2005

New Orleans

New Orleans LeveesNew Orleans Levees

Long Island Flooding PotentialLong Island Flooding PotentialNo FloodingNo Flooding

Long Island Flooding PotentialLong Island Flooding PotentialCategory 1Category 1

Long Island Flooding PotentialLong Island Flooding PotentialCategory 4Category 4

Saffir-Simpson ScaleSaffir-Simpson Scale

• Based on study of past storms• Ranks the relative intensities of hurricanes• Established based on observed

conditions.• Scale of 1 to 5

– Category 1 is least severe– Category 5 is most severe

• Rare• Not likely in the northeast because water

temperatures are too cool.

Saffir-Simpson ScaleSaffir-Simpson Scale

Category OneCategory One

• Wind speed: – 74-95 mph (119-153 km/h)

• Storm surge: – 4-5 feet above normal

• Central Pressure: 980 mb• Damage:

– Damage primarily to unanchored mobile homes, shrubbery, and trees along with some coastal road flooding and minor pier damage

• Examples: – Allison, 1995; Danny, 1997

Category TwoCategory Two

• Wind speed: – 96-110 mph (154-177 km/h)

• Central Pressure:– 965-979 mb


• Damage: – Roofing, door and window

damage to buildings; Considerable damage to shrubbery and trees, mobile homes, poorly constructed signs, and piers

– Examples: • Bonnie, Georges, 1998

Category ThreeCategory Three• Wind speed:

– 111-130 mph (178-209 km/h)• Central Pressure:

– 945-964 mb• Storm surge:

– 9-12 feet above normal• Damage:

– Structural damage to small residences and utility buildings; foliage blown off trees and large trees blown down; mobile homes destroyed

• Examples: – Roxanne, 1995; Fran, 1996;

Rita, 2005.

Category FourCategory Four

• Wind speed: 131-155 mph (210-249 km/h)

• Central Pressure:– 920-944 mb


• Damage: – Extensive damage to doors,

windows and lower floors of shoreline houses; total roof failures on small residences; shrubs, trees, and all signs blown down; mobile homes completely destroyed

• Examples: – Hugo, 1989, Luis, Felix, Opal,

1995, Emily, Katrina, Wilma 2005.

Hurricane KatrinaHurricane Katrina

A Category 5 over the Gulf of MexicoAugust 18, 2005

Came ashore as a category 4 stormand 8 hrs later was still a Category 1

Category FiveCategory Five• Wind speed:

– Greater than 155 mph (249 km/h)• Central Pressure:

– <920 mb• Storm surge:

– generally greater than 18 feet above normal

• Damage: – Complete roof failure on many

buildings and some complete building failures with small utility buildings blown over or away; severe and extensive window and door damage; mobile homes completely destroyed

• Examples: – Camille, 1969; Gilbert, 1988;

Andrew, 1992; Mitch, 1998

Atlantic Hurricanes that made Landfall as Atlantic Hurricanes that made Landfall as

Category 5 StormsCategory 5 Storms Name Date Landfall location Fatalities

Dean Aug. 21, 2007 Near Majahual, Mexico

At least 13

Gilbert Sept. 1, 1988 Cancun, Mexico 327

Edith Sept. 9, 1971 Nicaragua 30

Camille Aug. 17, 1969 Mississippi, USA 256

Janet Sept 28, 1955 Chetumal, Mexico >600

Unnamed Sept. 16, 1947 Bahamas 54

Labor Day Hurricane Sept. 3, 1935 Florida Keys 408

Unnamed Sept 5, 1932 Bahamas No Records

San Felipe-Okeechobee Hurricane

Sept. 13, 1928 Puerto Rico 2,166

11

11 Since records began in 1886 Since records began in 1886

The 20 Deadliest U.S. Hurricanes The 20 Deadliest U.S. Hurricanes (1900 – 2005)(1900 – 2005)

1938 New England Hurricane – 1938 New England Hurricane – (The Long Island Express)(The Long Island Express)

• The storm was tracked as it moved west from Africa and toward the Bahamas Islands.

• The U.S. Weather Bureau (now called the NWS)– Knew it was a powerful storm

• It had reached category 5 strength on September 19

– It was believed the hurricane would curve out to sea before reaching the Northeast.

– The Bureau tracked the storm on the 21st as it was off the coast of Norfolk, V.A

• Now a category 3 storm.

A large area of high pressureA large area of high pressure

• Was located over the Atlantic Ocean just east of the coast

• Kept the storm close to the coast and moving northeastward.

• Charlie Pierce, a young research forecaster for the Bureau– Concluded that the storm would not continue to move northeast

and curve out to sea but would instead track due north. – He was overruled by more senior meteorologists– The official forecast was for cloudy skies and gusty conditions –

• but no hurricane

Instead of Curving Out to Sea…Instead of Curving Out to Sea…• The storm moved due north and

accelerated in forward speed to 70 mph.

• In the history of hurricanes, this is the fastest known forward speed recorded.

• The incredible forward speed of the storm was 70 mph

• Winds to the east of the eye are moving from south to north.

– The same direction as the forward speed

– Added to the already powerful winds. Eastern Long Island and New England would later be hit with wind speeds that exceeded 180 mph!

Landfall on LI on Sept. 21Landfall on LI on Sept. 21• The eye was about 50 miles across and the hurricane was about

500 miles wide.• 3:30 PM which was just a few hours before astronomical high tide.

– High tide was even higher than usual because of the new moon (spring tides).

• Storm tides of 14 to 18 feet across most of the Long Island and Connecticut coast, with 18 to 25 foot tides from New London east to Cape Cod.

– Caused enormous storm surge• High tides combined with winds gusting over 180 mph• Waves between 30 and 50 feet pounded the coastline with millions of tons of

sea water, sweeping entire homes and families into the sea. • The impact of the storm surge was so powerful that it was actually recorded

on the earthquake seismograph at Fordham University in New York City.• Downtown Providence, Rhode Island was submerged under a storm tide of

nearly 20 feet.• Downtown Westhampton Beach, a mile inland, was under 8 feet of water!• Sections of Falmouth and New Bedford, Massachusetts were also

submerged under as much as 8 feet of water. • Rainfall resulted in severe river flooding across sections of New

York, Massachusetts, and Connecticut

Total Estimated DamageTotal Estimated Damage• 700 deaths (50 on L.I.), 708

injured• 4,500 homes, cottages, farms

destroyed; 15,000 damaged• 26,000 destroyed automobiles• 20,000 miles of electrical power

and telephone lines downed• 1,700 livestock and up to 750,000

chickens killed• $2,610,000 worth of fishing boats,

equipment, docks, and shore plants damaged or destroyed

• Half the entire apple crop destroyed at a cost of $2 million

Long Island’s CoastlineLong Island’s Coastline

• Creation of Shinnecock Inlet• Moriches Inlet was widened• Affects the flow of sand along the coastline (longshore currents)

– Depositional features– Erosional features

Shinnecock InletShinnecock Inlet

Moriches InletMoriches Inlet

NASA satellite image

Detecting and Tracking HurricanesDetecting and Tracking HurricanesSatellitesSatellites

Aircraft ReconnaissanceAircraft Reconnaissance“Hurricane Hunters”“Hurricane Hunters”

WC-130 Hercules ER-2

National Oceanic and Atmospheric Admin. (NOAA)

WP-3D Oriion

USAF NASA

Gulfstream G-IV

RADARRADAR

Hurricane Andrew (1992)

Data BuoysData Buoys

Hurricane PrepardnessHurricane Prepardness

Documents

Hurricanes