GEOS 110
NATURAL DISASTERS
 
Coastal Hazards-III
 
web sites: 1) coastal.er.usgs.gov/hurricanes 2) cirrus.sprl.umich.edu/wxnet/tropical.html
 
Tropical Cyclones
 - massive tropical storms (up to 600 miles in diameter) with rotary winds >74 mph.   One of Earth's mechanisms of redistributing solar energy.
 - called hurricanes in Atlantic and E. Pacific, typhoons in the W. Pacific, and    cyclones in the Indian Ocean and southern hemisphere.
 - occur in the late summer and fall when sea surface temperatures are maximum
 
 1) How a Hurricane Works
  - Three key requirements for development
   • seawater temperature of ?80°F in the upper 200 ft of the ocean
   • air must be both warm and humid
   • upper level winds are weak and blowing in the same direction as storm
  - development begins with a low-pressure zone of the the coast of W. Africa.    Cyclonic rotation, convergence and upward core spiral. Intensity depends    on the "efficiency" of the inflow, upward spiral, and outflow. The eye is    produced by a central column of cool air that sinks. Maximum winds are    found in the eye wall (10-25 miles wide). Rain bands.
 
 2) Hurricane Intensity
  - measured by the Saffir-Simpson scale; based on wind speed, air pressure,    and storm surge height. Category 1 to 5
 
 - Notable Hurricanes
  1900 Galveston, TX (~6,000 to 7,000 deaths; worst disaster in US history)
  1938 Long Island & New England (600 deaths)
  1992 Andrew (strong 4; >$25 billion in damages)
 
  only three category 5 events make landfall in N. America
   - 1935 Florida Keys (wiped out railroad; ~400 deaths)
   - 1969 Camille (~250 deaths)
   - 1988 Gilbert (hit Mexico, most intense storm ever recorded, lowest P [26.2 in]     and highest wind speed [+200 mph]; developed an inner and outer eye).
Prof. Gorring         Apr. 30, 1998
GEOS 110
NATURAL DISASTERS
 
Coastal Hazards-IV
 
Hurricane Hazards
 - high winds, river flooding, tornadoes, storm surge
 
  storm surge: large mound of seawater that builds up beneath the eye. Bulge of    water with large waves on top. Most dangerous; Causes 90% of deaths.
   - Three processes contribute to storm surge:
    • the very low air pressure allows water to "rise"
    • converging surface winds push water up beneath the eye
    • large, wind-driven waves that transports water landward
   - Magnified by coincidence with high tide or depending on the shape of     coastline and the slope of the seafloor near coast. Concave      shorelines and shallow, narrowing bays are vulnerable.
   - When hurricane makes landfall perpendicular to coast, winds and      storm surge are more intense on the "right side" of storm.    - Surge levels can now be calculated by computer models
    (SLOSH) Sea, Lake, and Overland Surges from Hurricanes
 

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College of Science and Mathematics - Montclair State University
This page was last modified on August 05, 1998 05:14