Local weather forecast by
"City, St" or zip code |
|
Search by city or zip code. Press enter or select the go button to submit request
|
|
You are at NWS Houston/Galveston »
Tropical Weather» Tropical Cyclone Threats
Tropical Cyclone Threats
Storm Surge
Storm surge is a large dome of water often 50 to 100 miles wide that sweeps across the
coastline near where a hurricane makes landfall. Storm surge can range from 4 to 6 feet
for a minimal hurricane to greater than 20 feet for the stronger ones. The surge of high
water topped by waves is devastating. The stronger the hurricane and the shallower
the offshore water, the higher the surge will be. Along the immediate coast, storm surge
is the greatest threat to life and property, even more so than the high winds!
--Over 8000 people were killed in the Galveston Hurricane of 1900, most by storm surge.
--Hurricane Camille produced a 25-foot storm surge in Mississippi.
--Hurricane Hugo in 1989 generated a 20-foot storm tide in South Carolina.
Rainfall and Flooding
Hurricanes are capable of producing copious amounts of flash flooding rainfall. During landfall,
a hurricane rainfall of 10 to 15 inches or more is common. Obviously, if the storm is large and
moving slowly--less than 10 mph--the rainfall amounts from a well- organized storm are likely
to be even more excessive. To get a generic estimate of the rainfall amount (in inches) that
can be expected, divide the storm's forward motion into 100.
Fact: Tropical Storm Claudette (1979) brought 45 inches of rain to an area near Alvin, Texas,
contributing to more than 600 million in damage.
Tornadoes
Hurricanes also produce tornadoes, which add to the hurricanes destructive power. Typically,
the more intense a hurricane is, the greater the tornado threat. When a hurricane brings its
winds inland, the fast-moving air hits terrain and structures, causing a frictional convergence
which enhances lifting. Frictional convergence may be at least a contributing factor to
tornado formation in hurricanes. The greatest concentration of tornadoes occur in right
front quadrant of the hurricane.
Hurricane Winds
Hurricane winds are a force to be reckoned with by coastal communities deciding how
strong their structures should be. As winds increase, pressure against objects is added
at a disproportionate rate. Pressure against a wall mounts with the square of windspeed
so that a threefold increase in windspeed gives a ninefold increase in pressure. Thus,
a 25 mph wind causes about 1.6 pounds of pressure per square foot. A four by eight
sheet of plywood will be pushed by a weight of 50 pounds. In 75 mph winds, that
force becomes 450 pounds, and in 125 mph winds, it becomes 1250 pounds. For
some structures, this force is enough to cause failure.
|
|
weather.gov 
National Weather Service Forecast Office
