Tropical Cyclones

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Tropical Cyclones

• Dr. Benjamin R. Lintner
• 12/08/09

Hurricane Epsilon photographed on 12/03/05 from
the ISS (NASA)
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What is a tropical cyclone?

• A storm system originating in the Tropics with a
  large low-pressure center and thunderstorms
  producing strong winds and rainfall
• The most intense tropical cyclones are called
  different names regionally
• Hurricane North America
• Typhoon Eastern Asia
• Severe Tropical Cyclone India/Australia
• Also willy-willy Australia, bagyo/baguio
  Philippines

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Etymology of Hurricane

• Taino in Caribbean juracán
• Maya huracan or hurakan

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Hurricane Size and Strength

• Extratropical cyclones 1,000-10,000 km
• Tornadoes 1/4 km
• Hurricanes 800-1,000 km
• While hurricanes are neither the largest storms
  nor the strongest, for their size and strength
  they are the most destructive

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Hurricane Development

• Tropical disturbance cluster of thunderstorms
  with organized circulation
• Tropical depression winds between 20-34 knots
  system is numbered
• Tropical storm winds between 35-64 knots system
  is named
• Hurricane winds greater than 64 knots
• Saffir-Sampson Intensity Scale 5 categories,
  with 1 weakest and 5 strongest major hurricane
  status category 3

Termed cyclogenesis
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Katrinas evolution

• 08/23/05 TD12 over SE Bahamas interaction of
  tropical wave with remnants of TD10
• 08/24 Upgraded to TS and named Katrina
• 08/25 Upgraded to H 2 hours before landfall on
  the east coast of Florida
• 08/25-08/26 Weakening over land followed by
  restrengthening upon entry into the southeastern
  Gulf of Mexico
• 08/27 Category 3 (major hurricane)
• 08/28 Category 5
• 08/29 Second landfall (Cat 3) near
  Buras-Triumph, LA hurricane force winds
  extending out 190 km maintained hurricane
  strength 240 km inland
• 08/31 last distinguishable presentation near
  Great Lakes on 08/31 when absorbed by a passing
  midlatitude front

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Hurricane Anatomy
Hurricane Dean on 08/20/07

• The low-pressure center is called the eye, which
  has calm winds and relatively clear skies
• Immediately surrounding the eye is the eye wall,
  the area of strongest winds and most intense
  rainfall
• Arcs of thunderstorms extending outward are call
  spiral bands

eye and eye wall
spiral bands
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Hurricane Cross-Section
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Inside Katrinas eye!
Category 5, w/ sustained winds 265 km/hr
gusts to 305 km/hr) Minimum central pressure of
902 mb (4th most powerful Atlantic hurricane at
the time)
Taken on 08/28/05 by a crewperson on the NOAA P3
Hurricane Hunter
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Recipe for a hurricane
Lisa Gardner/Windows to the Universe
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Where when are they born?
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Where are they likely to go?
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Atlantic Cyclone Tracks (00-08)
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Hurricane Wind Impacts

• Category 1 64-82 knots/119-153 km/hr
• Damaging winds expected some damage (minor) to
  buildings, snapped branches or uprooted trees
  local power outages
• Category 2 83-95 knots/154-177 km/hr
• Strong winds produce widespread damage damage to
  buildings, glass window breakage in high rises
  widespread power outages for days
• Category 3 96-113 knots/178-209 km/hr
• Dangerous winds cause extensive damage
  structural damage to buildings and older mobile
  homes destroyed many trees snapped or uprooted
  total power loss for days to weeks
• Category 4 114-135 knots/210-249 km/hr
• Extremely dangerous winds cause extensive damage
  some wall and roof failures all signs blown
  down most trees snapped or uprooted power loss
  for weeks
• Category 5 gt135 knots/250 km/hr
• Catastrophic damage many buildings completely
  destroyed nearly all trees snapped/uprooted
  power loss for months

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Storm surge

• Onshore, wind-induced flow of water
• Responsible (along with flooding) for 90 of
  hurricane-related mortality

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Global warming and hurricanes

• As sea surface temperature rise, more fuelfor
  hurricanes?
• Would this change frequency of storms, their
  intensity, or both?
• And what about changes to other factors?
• Difficult to assess from currently-available
  measurements
• Atlantic and northeast Pacific are well
  instrumented, but other regions less so
• Issues with integrating historical
  (pre-satellite) observations