Tropical Cyclones Hurricanes

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Tropical Cyclones (Hurricanes)

• Flight inside the eye of a hurricane

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• Strong tropical storms are called hurricanes in
  the Atlantic and Eastern Pacific, typhoons over
  the western Pacific, and cyclones near Australia
  and the Indian Ocean.
• Energy from a single hurricane exceeds the annual
  electrical consumption of north america
• Hurricanes depend on a large pool of warm water
  so dont form where those conditions dont exist

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• Hurricanes have sustained winds greater than 64
  knots (120 kmh) with central pressures from 950
  to 870 hPa
• They are about 600 km wide and last several days
• Most energy comes from latent heat release
• Since tropical oceans have greatest SSTs and
  evaporation rates in late summer and early fall,
  this is why they tend to occur in August and
  September in NH and January-March in the SH

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• Contain a large number of thunderstorms in spiral
  bands around the central Low
• There are no fronts associated with them
• They are warm core cyclones (mid-latitude
  cyclones are cold core)
• Due to hydrostatic law, the pressure decreases
  slowly with height over the low, so that the
  storm disappears with altitude and becomes a High
  with anticyclonic outflow

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• Hurricanes start as tropical disturbances
  disorganized groups of thunderstorms that move to
  the west
• They intensify into tropical depressions and
  then tropical storms if they encounter warm
  surface water

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Conditions for Hurricane Formation

• Ocean has a deep surface layer (10s of m) with
  SST above 27 degrees C. (equatorward of 20
  degrees latitude)
• Need some Coriolis force to prevent flow from H ?
  L filling in the Low (not between 0-5 degrees
  latitude)
• Unstable troposphere (no cold currents or
  upwelling)
• No strong wind shear (change in wind with height)
  which would disrupt convection

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Movement Dissipation

• Guided by trade winds, so migrate westward
• Once developed will be guided by upper winds so
  move poleward
• Weaken as encounter low SST or land (reduce
  latent heat)

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• Major threat is due to high winds, heavy
  precipitation, and especially storm surge
• Storm surge cause by wind pushing water on shore
  and by low pressure