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

TROPICAL CYCLONES ON PLANET EARTH
3.13, although the region of most destruction potential is concentrated close to
the center of the storm in the region of the eye wall.
The largest radius of tropical storm winds (greater than 39 mph) was 680
miles (1100 kilometers) in Typhoon Tip in the western Pacific in October 1979
(Holl<strong>and</strong> 1993a). The smallest was Tropical Cyclone Tracy which made
l<strong>and</strong>fall in Darwin, Australia in December 1974 with a radius of tropical
storm winds of 31 miles (50 kilometers). The relative sizes of these storms,
along with the 1995 Labor Day Hurricane which crossed the Florida Keys,
the New Engl<strong>and</strong> Hurricane of 1938, Camille (1969), Gilbert (1988) which
made l<strong>and</strong>fall in Mexico, <strong>and</strong> Andrew (1992) are shown in Figure 3.15. The
most intense tropical cyclone on record, as measured by its central pressure,
was also Typhoon Tip (870 mb). In the Atlantic Basin, it was Gilbert in 1988
with 888 mb (Lawrence <strong>and</strong> Gross, 1989; Willoughby, Masters <strong>and</strong> L<strong>and</strong>sea
1989). The longest lived tropical cyclone on record was John, which lasted for
31 days (August-September 1994) in the Pa~c Ocean. In the Atlantic Ocean
Basin, it was was Hurricane Ginger in 197.1. which lasted for 30 days.
3.3.3 Tropical cyclones in the Atlantic Ocean Basin
At latitudes around 30oN in the Atlantic Ocean, two large relatively stationary
high pressure systems, which extend upward throughout the lower atmosphere
(i.e. the troposphere) commonly exist throughout the year. High pressure
systems exhibit a clockwise wind flow around their center. These pressure
systems are popularly known as the Azores High <strong>and</strong> the Bermuda High since
their centers of highest pressure are often located near those isl<strong>and</strong>s. In the
Northern Hemisphere, south of these high pressure regions, trade winds blow
from east to west. These are called trade winds because they were used by
sailing vessels to travel between Europe <strong>and</strong> the New World prior to the
1800s.
The latitude of the highest pressure of the Azores <strong>and</strong> Bermuda Highs moves
north <strong>and</strong> south with the seasons, with its northernmost location ocCurring
around August. A lag of about two months with respect to the June solstice
(which is when solar radiation is greatest in the Northern Hemisphere) is
associated with the time of maximum ocean surface temperatures. This lag
occurs because the ocean <strong>and</strong> the atmosphere take time to warm, analogous to
the observation that our warmest temperatures during the day occur after noon
(<strong>and</strong> similarly the warmest temperatures at most locations in the Northern
Hemisphere occur in July <strong>and</strong> August). Thus in the western Atlantic, the ocean
is warmest in August <strong>and</strong> early September.
Tropical storms <strong>and</strong> hurricanes frequently develop from surface low
pressure systems that move westward off the west Mrican coast, called
tropical waves (e.g. see Pasch <strong>and</strong> Avila 1994; Avila <strong>and</strong> Pasch 1995). The
systems move west in the trade wind region. Often such low pressure systems
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