HURRICANES
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Hurricane
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Intense storm of tropical origin
Winds >64 knots (74mph)
Forms:
 Warm Northern Atlantic
 Eastern North Pacific Oceans
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Eye
Eye Wall
Spiral Rain bands
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Eye:
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Calm
As move into eye:
 Air temperature: Increases
 Wind speeds: Slow or Slacken
 Rainfall: Ceases or Stops
 Sky appearance: Sky brightens
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Eye Wall:
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Adjacent to the eye
Thunderstorms
Whirl around the center and upward (15km or
49,000)
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Spiral Rain bands:
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Surface winds:
 Increase in speed
 Blow counterclockwise (Northern Hemisphere)
 Inward toward its center
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Hurricanes form:
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Over warm tropical waters
Light winds converge
Humidity is high in a deep layer
WINDS ALOFT ARE WEAK
Driving Force: latent heat
Hurricane strength:
Grow in strength
 Decrease in strength
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Hurricanes mostly form over tropical oceans
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EXCEPT: Southern Atlantic & Eastern South Pacific
North Pacific and North Atlantic
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Steered by EASTERLY winds and move WEST
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Hurricane Path:
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Swing north around the subtropical high
 Caught in the westerly flow
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Actual path:
 Determined: storm structure and interaction with the
environment
 Eastern North Pacific: normally westward away from
the coast
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The Hawaiian Islands:
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Direct path of many eastern Pacific hurricanes and
tropic storms
Weaken before hits islands
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Question:
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Northward moving hurricane over the Atlantic
survives longer than its counterpart at the same
latitude over the Eastern Pacific
 The surface water over the Atlantic is much warmer
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When on approach from the east:
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Highest winds are usually on its north (poleward)
 Winds propelling storm push added with winds on the
north side and subtract from the winds on the south
(equator) side.
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Gloria 9/27/1985
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Moving northward but the net transport of water
directed eastward toward the coast
 Ekman Spiral and Coriolis
 North wind caused a net transport of water toward the
shore
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Swells
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Large waves (10-15m or 33-49ft)
Move outward away from the storm
Damage
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Wind
Waves
High Seas
Flooding
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Flooding (Most destructive)
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Aided by the low pressure of the storm
Low pressure regions ocean level rise ½ meter
Storm Surge
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High water + high winds and the net transport of
water toward the coast
Storm Surge- abnormal rise of several meters in the
ocean level, which engulfs low-lying areas
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Storm Surge
Before
During
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Other Damage
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Tornadoes
 ~ ¼ US hurricanes tornadoes
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Why?
 Not quite known.
 Surface topography may play a role by initiating the
convergence and so the rising of surface air.
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Hurricane Watch
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Poses a direct threat to an area
24-48 hours before the storm arrives
 National Hurricane Center (Florida)
 Pacific Hurricane Center (Hawaii)
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Hurricane Warning
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Appears to strike an area within 24 hours
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Saffir-Simpson Scale
“Tropical Depression”
“Tropical Storm” (given name)
Ranked from 1-5
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Category 1- Lowest rank
Category 3- Major hurricane
Category 5- Severe damage
Scale
Central Pressure
mb
in.
1
≥980
2
965-979
3
945-964
4
920-944
5
< 920
Winds
mi/hr
knots
Storm Surge
ft
m
Damage
Damage mainly to trees, shrubbery,
and unanchored mobile homes
≥28.94
74-95
64-82
4-5
~1.5
Some trees blown down; major
damage to exposed mobile homes,
28.5-28.91 96-110 83-95
6-8 ~2.0-2.5 some damage to roofs of buildings
Foliage removed from trees; large
trees blown down; mobile homes
destroyed; some structural damage
27.91-28.47 111-130 96-113 9-12 ~2.5-4.0
to small buildings
All signs blown down; extensive
damage to roofs, windows, and
doors; complete destruction of mobile
homes; flooding inland as far as
10km (6mi); major damage to lower
27.17-27.88 131-155 114-135 13-18 ~4.0-5.5
floors of structures near shore.
Severe damage to windows and
doors, extensive damage to roofs of
homes and industrial buildings; small
buildings overturned and blown
away; major damage to lower floors
of all structures less than 4.5m (15ft)
above sea level within 500m of
< 27.17
>155
>135
>18
>5.5
shore.
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Assigned “tropical storm” strength
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Previous naming methods:
 Latitudes and longitudes
 Letters of the alphabet (WWII)
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By 1953
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Female names used using the alphabet
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1978
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1979
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Eastern Pacific used both male and female
North Atlantic began this alternating practice as well
Names retired
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Hurricanes are tropical cyclones with winds
that exceed 64 knots (74mph)
Consists of a mass organized thunderstorms
that spiral in toward the extreme low pressure
of the storm’s eye
Storms are given a name at the Tropical Storm
category
The energy source that drives hurricanes comes
from primarily a release of latent heat
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In the Northern Hemisphere Hurricanes blow
counterclockwise around the eye
In the eye the weather is calm, no rain, no
wind, sunny
Eye wall: Intense rain, wind, and
thunderstorm
Hurricanes develop in warm tropical waters
Hurricanes can spawn tornadoes
Weaken over cold water and land
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Hurricane damage
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Storm Surge, Wind, Flooding
Usually the most damage is caused by huge waves
and flooding with the storm surge causes the most
damage
Difference between hurricane and typhoon
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Location:
 western North Pacific areas- typhoon
 Australia and India- cyclones
• http://geology.com/hurricanes/named-hurricane-fran.gif
• http://ehsjournal.org/wp-content/uploads/2010/07/NOAA-Hurricane-Ivan09-15-2004-1515z.jpg
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• http://hurricanehazel.ca/test_hurricane_knowledge/eyewall.jpg
• http://www.nasa.gov/images/content/138612main_okelley_graph_lg.jpg
• http://worldlywise.pbworks.com/f/1271536572/cyclone_map.gif
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• http://cloud.graphicleftovers.com/24766/1020755/hurricane-warning-stopsign.jpg
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rale.svg/200px-Ekman_spirale.svg.png
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• http://ttnewsflash.com/wp-content/uploads/2012/10/Hurricane-names.jpg
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