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43 What determines the movement of tropical cyclones?




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This article is from the Storms FAQ, by Chris Landsea landsea@aoml.noaa.gov with numerous contributions by others.

43 What determines the movement of tropical cyclones?

Tropical cyclones - to a first approximation - can be thought of as
being steered by the surrounding environmental flow throughout the depth
of the troposphere (from the surface to about 12 km or 8 mi). Dr. Neil
Frank, former director of the U.S. National Hurricane Center, used the
analogy that the movement of hurricanes is like a leaf being steered by
the currents in the stream, except that for a hurricane the stream has no
set boundaries.

In the tropical latitudes (typically equatorward of 20-25 N or S),
tropical cyclones usually move toward the west with a slight poleward
component. This is because there exists an axis of high pressure called
the subtropical ridge that extends east-west poleward of the storm. On
the equatorward side of the subtropical ridge, general easterly winds
prevail. However, if the subtropical ridge is weak - oftentimes due to
a trough in the jet stream - the tropical cyclone may turn poleward and
then recurve back toward the east. On the poleward side of the
subtropical ridge, westerly winds prevail thus steering the tropical
cyclone back to the east. These westerly winds are the same ones that
typically bring extratropical cyclones with their cold and warm fronts
from west to east.

Many times it is difficult to tell whether a trough will allow the
tropical cyclone to recurve back out to sea (for those folks on the
eastern edges of continents) or whether the tropical cyclone will
continue straight ahead and make landfall.

For more non-technical information on the movement of tropical cyclones,
see Pielke's _The Hurricane_. For a more detailed, technical summary
on the controls on tropical cyclone motion, see Elsberry's chapter in
_Global Perspectives on Tropical Cyclones_. Both books are detailed in
Part II of the FAQ.

 

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