Hurricanes: Their Nature and Impacts on Society - Climate Science ...

HURRICANE Fa RECASTS
While the news media often attribute hurricanes "with a life of their own",
they are, of course, generally well-behaved natural phenomena <strong>and</strong>, to a large
extent, their movement can be explained by the steering currents alone, as
shown in the two examples discussed in the last two paragraphs. The difficulty
in forecasting their motion occurs when the steering currents are weak <strong>and</strong> illdefined
<strong>and</strong>/or when the future state of the steering currents is uncertain. In
addition, the need to forecast fairly precise points of l<strong>and</strong>fall to aid emergency
planning also contributes to the difficult task of hurricane forecasting.
Tropical cyclones occasionally undergo rapid acceleration in forward
motion. This happens when the storm becomes linked to a strong mid-latitude
weather system. In addition, tropical cyclones can become absorbed into
developing mid-latitude storms thereby infusing added moisture <strong>and</strong> wind
energy from the tropical cyclone <strong>and</strong> resulting in a more intense mid-latitude
storm than otherwise would occur.
An example of a storm that accelerated rapidly out of the tropics was the
New Engl<strong>and</strong> hurricane of 1938. The development of strong, southwesterly
winds to the west of this hurricane, associated with a developing mid-latitude
storm, resulted in its rapid acceleration to the north at a forward speed of
more than 60 mph (27 meters per second). The storm crossed Long Isl<strong>and</strong>,
New York with little warning, resulting in more than 600 deaths in New
Engl<strong>and</strong> (see Chapter 2).
In 1954, Hurricane Hazel also underwent a similar rapid acceleration to a
speed of 60 mph (27 meters per second), as strong south to southwesterly
winds developed to the west of the storm. Hazel crossed the North Carolina
coastline at 9:25 am on 15 October, <strong>and</strong> reached Toronto, Canada only 14
hours later where it resulted in 80 deaths (Joe et al. 1995). At that time, it was
the most destructive hurricane to reach the North Carolina coast. Every
fishing pier was destroyed over a distance of 170 miles (270 km) from Myrtle
Beach, South Carolina to Cedar Isl<strong>and</strong>, North Carolina. All traces of civilization
were practically annihilated at the immediate waterfront between Cape
Fear <strong>and</strong> the South Carolina state line. In 1989, Hurricane Hugo accelerated
onto the South Carolina coast at Charleston in association with southeasterly
winds caused by a low pressure area in the northeastern Gulf of Mexico, in
combination with the Bermuda High to the northeast.
4.3 INTERACnON OF nm STEERING CURRENT
AND nm HURRICANE
If the steering current in the immediate vicinity of the stonn was constant, its
influence on stonn motion would be relatively straightforward. Unfortunately,
this is generally not the case. The steering current speed <strong>and</strong> direction are
never constant <strong>and</strong> change both in location <strong>and</strong> time. If the steering current,
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