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

102 HURRICANES: THEIR NATURE AND IMPACT ON SOCIETY
storm. The winds representing the steering current are easterly in the absence
of the isl<strong>and</strong>. With the isl<strong>and</strong> present to block the flow (even without a
hurricane present) the winds would turn southerly to the east of the isl<strong>and</strong>.
With the hurricane present as shown, the circulation around the storm,
interacting with the simulated terrain, resulted in the path plotted in the figure,
which is to the right of the steering current in the absence of the storm. In the
absence of the isl<strong>and</strong>, the hurricane would have moved on a general westward
track. In the Atlantic region, terrain effects of this type occur associated with
the larger isl<strong>and</strong>s of the Caribbean (Cuba, Hispafiola). Flatter l<strong>and</strong>scape, such
as the Yucatan Peninsula <strong>and</strong> Florida, <strong>and</strong> the smaller isl<strong>and</strong>s of the
Caribbean <strong>and</strong> Atlantic have much less of an effect on cyclone tracks.
4.4 INTERNAL F1..0W
Even when the steering current is relatively uniform <strong>and</strong> steady, however,
hurricane motion is often somewhat irregular. For example, Figure 4.6 illustrates
the oscillation of the movement of the eye of Hurricane Dora (1964) as
it progressed on a general track westward towards the upper east coast of
Florida. This oscillation is primarily due to forces within the hurricane. In
Hurricane Anita (1977), the eye <strong>and</strong> eye wall were observed by aircraft to
have an oscillation around the mean track with an amplitude of 3 miles (5
km) <strong>and</strong> a period of 6 hours (Willoughby 1979). This small-scale irregular
behavior of the center of the storm has been attributed to the thunderstorms
<strong>and</strong> strong winds in the eye wall region, which causes the center to deviate
short distances to the left or right of its track, similar to the motion of a
spinning top. The larger circulation envelope of the hurricane, with its much
greater inertia, more closely follows the steering current <strong>and</strong> tends to force the
eye wall back towards the center of the larger circulation.
4.5 TROPICAL CYCLONE TRACK, INTENSITY, AND
SEASONAL FORECASTING
Hurricane predictions in the United States are prepared at the National
Hurricane Center in Miami, Florida for tropical cyclones in the Gulf of
Mexico, the Caribbean <strong>and</strong> the Atlantic Ocean <strong>and</strong> the eastern Pacific (Figure
4.7). Other regions of responsibility are shown in Appendix D.
4.5.1 Tropical cyclone track predictions
The National Hurricane Center utilizes a suite of models to forecast tropical
cyclone tracks (DeMaria 1995; Aberson <strong>and</strong> DeMaria 1994). They include
one based on climatology <strong>and</strong> persistence (CLIPER), a statistical model which