Hurricanes
Tropical 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 Hurricanes
• Starting in 1953
– NWS started using female names
• Prior 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 1979
– Male and female names were included in lists for the Atlantic and
Gulf of Mexico
Tropical Storm and Hurricane Names for the Atlantic,
Gulf 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 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 Hurricanes
• If more than 21 named tropical cyclones
occur 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-season
– The name used is based on the calendar year
• Retiring 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 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.
Hurricane Fran
Visible Image 9/5/96
FL
Cuba
•
•
•
•
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
The Structure of a Hurricane:
Convective Rain Bands
Tropical moisture spiraling inward creates rain bands that pinwheel around
the storm center
The Structure of a Hurricane:
The 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 Wall
Produces the most intense rainfall
and greatest wind speeds
Katrina Eye Wall - 2005
Hurricane Charley - 2002
The Structure of a Hurricane:
Outflow
Outflow prevents the convergent flow at lower levels from “filling in” the storm.
The Structure of a Hurricane:
The Eye
Average Diameter is
20 to 30 miles (32 to 48 km)
• 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.
Can you identify when the eye passed?
Eye
Wind speeds recorded by a data buoy in the eastern
Gulf of Mexico during the passage of Hurricane Kate (1985)
Hurricane Wilma
October 2005
Eye
The record for the lowest surface air pressure for an Atlantic Hurricane,
882.0 mb, was recorded in the eye on Oct. 18
Vertical Section and Associated Patterns of
Wind, Pressure, and Rain
Hurricane Formation and Decay
Cooperative Program for Operational Meteorology, Education and Training
Hurricanes 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 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 Disturbances
Africa
S. America
• 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
Disturbances Can Become Easterly Waves
•
•
•
•
Streamlines (arrows) show lowlevel 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 Inversions
Prevent 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
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 Decay
(1)
(2)
(3)
Hurricane Allen (1980) loses strength as it moves over land.
• 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
Storm Tracks For 2005 - 28 Named Storms!
•
Influenced by
– Trade Winds
– Prevailing Southwesterlies
– Jet Stream
– Other Highs and Lows
Hurricane Destruction
• Depends on
– Strength of the Storm
– Size and population density of the area
affected
– Nearshore bottom configuration
Wind Damage
Hurricane Andrew
•
•
•
•
•
Hurricane Wilma
The most obvious type of damage
Debris becomes flying missiles
Mobile homes are particularly vulnerable
High rise buildings, especially upper floors,
Damage to the roof of the Superdome
areVulnerable
from Hurricane Katrina
Tornadoes that are produced by some
hurricanes contribute to the storms damage
Hurricane Winds
Storm surge will be greatest along the
coastline hit by the right side of the hurricane
Storm 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
Hurricane of 1900
An unexpected Category 4 storm
Galveston Seawall
25-Storm Surge From Hurricane Camille (1969)
Before
The Richelieu Apartments
in Pass Chistian, MS
After
Katrina Storm Surge and Flooding
Katrina Flooded an Estimated 80% of
New Orleans in 2005
New Orleans
New Orleans Levees
Long Island Flooding Potential
No Flooding
Long Island Flooding Potential
Category 1
Long Island Flooding Potential
Category 4
Saffir-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 Scale
Category 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 Two
• Wind speed:
– 96-110 mph (154-177 km/h)
• Central Pressure:
– 965-979 mb
• Storm surge:
– 6-8 feet above normal
• 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 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 Four
•
•
Wind speed: 131-155 mph (210249 km/h)
Central Pressure:
– 920-944 mb
•
Storm surge:
– 13-18 feet above normal
•
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 Katrina
A Category 5 over the Gulf of Mexico
August 18, 2005
Came ashore as a category 4 storm
and 8 hrs later was still a Category 1
Category 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
1
Category 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 FelipeOkeechobee Hurricane
Sept. 13, 1928
Puerto Rico
2,166
1
Since records began in 1886
The 20 Deadliest U.S. Hurricanes
(1900 – 2005)
1938 New England Hurricane –
(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 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…
•
•
•
•
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. 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 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 Coastline
•
•
•
Creation of Shinnecock Inlet
Moriches Inlet was widened
Affects the flow of sand along the coastline (longshore currents)
– Depositional features
– Erosional features
Shinnecock Inlet
Moriches Inlet
NASA satellite image
Detecting and Tracking Hurricanes
Satellites
Aircraft Reconnaissance
“Hurricane Hunters”
WC-130 Hercules
ER-2
USAF
Gulfstream G-IV
NASA
WP-3D Oriion
National Oceanic and Atmospheric Admin. (NOAA)
RADAR
Hurricane Andrew (1992)
Data Buoys
Hurricane Prepardness