Geoscience Reference
In-Depth Information
storms, and hurricanes. These will assist in prompting actions needed to protect
lives and the public before, during, and after tropical cyclone events.
Tropical Storm Watch—Issued when tropical storm conditions (sustained
winds of 39 mph to 73 mph) are possible within the specified coastal area
within 48 hours.
Tropical Storm Warning—Issued when tropical storm conditions (sustained
winds of 39 mph to 73 mph) are expected somewhere within the specified
coastal area within 36 hours.
Hurricane Watch—Issued when hurricane conditions (sustained winds of 74
mph or higher) are possible within the specified coastal area. Because hurri-
cane preparedness activities become difficult once winds reach tropical storm
force, the hurricane watch is issued 48 hours in advance of the anticipated
onset of tropical-storm-force winds.
Hurricane Warning—An announcement that hurricane conditions (sus-
tained winds of 74 mph or higher) are expected somewhere within the speci-
fied coastal area. Because hurricane preparedness activities become difficult
once winds reach tropical storm force, the hurricane warning is issued 36
hours in advance of the anticipated onset of tropical-storm-force winds.
Unlike many hazards, hurricanes typically have a warning period that can last
several days. However, it is imperative that the Emergency Manager not wait until
there is a threat of a landfalling tropical storm or hurricane before preparing his or
her organization and the public. Tropical storms and hurricanes have two primary
facets (although not the only facets), both of which can contribute to extensive
damage and loss of life:
Storm Surge and Storm Tide
Storm surge is the rise of water that results from the wind pushing water
ashore. This surge of water can be much larger than the predicted astronomi-
cal tides. Storm tide is the combination of the astronomical tide with the
storm surge (Figure 5.3). These phenomena are typically coupled with batter-
ing waves, which exacerbate damages onset by the storm surge or storm tide.
There are several variables that influence the maximum potential storm
surge that can be received at a particular location. Slight deviations in these
variables can vastly change the amount of storm surge received onshore.
These variables include storm intensity, storm size (radius of winds), forward
speed, angle of approach to the coast, the shape of the coastal geography (bays
and estuaries can cause a buildup of water), and the width and depth of the
continental shelf (shallow areas in the continental shelf can cause quicker
build up of storm surge).
To determine a location's vulnerability, the Emergency Manager can refer
to the Sea Lake and Overland Surges from Hurricanes (SLOSH) model. This
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