Part 4. Disturbances

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Part 4. Disturbances

• Chapter 12
• Tropical Storms and Hurricanes

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Introduction

• Hurricanes are responsible for astonishing
  amounts of property damage and loss of life in
  many regions of the world

Propagation of Hurricane Andrew Andrew caused
major damage in Florida and Louisiana
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• Hurricanes around the globe
• Atlantic - hurricanes
• Western Pacific typhoons highest frequency
  region
• Indian Ocean and Australia cyclones
• South Atlantic - almost none

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Tropical cyclone genesis areas and related storm
tracks
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• The tropical setting where tropical storms
  usually form
• Subsidence (trade wind) inversion on the east
  side of the subtropical highs traps cooler, moist
  air (marine layer) at the ocean surface
• On the western sides of the ocean basins, the
  marine layer tends to be warmer and thicker due
  to higher ocean temperatures -- more hurricanes
  tend to develop here

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Tropical cyclone structure

• Hurricane characteristics
• Sustained winds greater than 120 km/hr (74 mph)
• Average diameter 600 km (350 mi)
• Central pressure 950 mb to 870 mb

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Vertical temperature profile across a hurricane
Hurricane eye -- average diameter 25 km (15
miles) -- area of descending air -- strongest
winds in eye wall (clouds just outside eye)
Hurricane eye
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Tropical cyclone air trajectories with height
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The double eye wall of Hurricane Emily
Hurricane with a double eye wall (occurs near
maximum strength)
eye walls
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Hot tower in Hurricane Rita
A hot tower is a part of the eye wall that rises
to great height (up to 36 km) it can indicate
hurricane strengthening
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• Hurricane Formation
• Steps in the formation of hurricanes
• Tropical disturbance associated with an easterly
  wave in the upper air winds
• Tropical depression -- at least one closed isobar
  
• Tropical storm -- winds greater than 37 mph
• Hurricane (typhoon, cyclone) -- winds greater
  than 74 mph

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An easterly wave
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• Conditions Necessary for Hurricane Formation
• Warm ocean water (gt 77oF)
• Latent heat release
• Most frequent in late summer and early autumn
• Formation equatorward of 5o
• Unstable atmosphere without vertical shear
• Once formed self-propagating system until it
  runs out of warm water

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Erratic hurricane path examples
Hurricane paths are controlled by trade winds,
upper air flow, air pressure systems and ocean
temperatures they can be quite erratic.
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After it came onshore, hurricane Camille merged
with a frontal cyclone along a stationary front,
causing massive loss of life and property damage
due to heavy rains and flooding.
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Predominant Atlantic hurricane paths
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• Hurricane Destruction and Fatalities are caused
  by several factors
• Wind
• Heavy rain
• Tornadoes
• Right front quadrant
• Storm surge
• Rise in water level associated with pressure drop
  

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Wind speed variations by quadrant
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Blown sand from Hurricane Katrina
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Average tornado locations relative to hurricane
storm center
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Atlantic hurricane frequencies
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End of Chapter 12 Understanding Weather and
Climate 4th EditionEdward Aguado and James E.
Burt