If there is so much uncertainty in forecasting the path of a disturbance
at sea, how much more uncertain must it be on land? Elaborate statistics
of the average daily movement of various types of storms have been
officially published. The average speed of storms (not wind speeds)
across the United States is 11 metres per second or 25 miles an hour.
Storms travel more rapidly in winter than in summer, about half again as
fast; that is, summer storms travel 20 miles, and winter storms 30
miles, an hour.
[Illustration: FIG. 7. LIPS--THE SOUTHWEST WIND]
The paths vary widely; from the Gulf storms moving northeast and West
Indian hurricanes recurving on the southern coast, to the storms from
Alberta and the west which move south and east. Ten types of storms,
classified according to the place of origin, are recognized by the
official forecasters of the United States. These are North Pacific,
Alberta, Northern Rocky Mountain, Colorado, Central, South Pacific,
Texas, East Gulf, South Atlantic and West Indian Hurricanes. A better
nomenclature would be (1) Alberta, (2) Washington, (3) Kootenay, (4)
Utah, (5) Kansas, (6) California, (7) Texas, (8) Louisiana, (9)
Florida, and (10) Hurricanes.
HURRICANES
Type 10 is the general class of tropical storms occurring chiefly in the
summer and fall which, drifting west, slowly work northward. Similar
storms are the typhoons and baguios of the East Indian and China Seas.
The path and point of recurvature will be determined by the position of
the Bermuda Hyperbar, that is, the seasonal anticyclone of the Atlantic.
This accounts for the swinging east and north of these tracks as the
season progresses; for the hyperbar is slowly displaced east, the
maximum displacement occurring in September.
[Illustration: BASE MAP BY GOODE
FIG. 8. ALL STORMS LEAD TO NEW ENGLAND]
Individual anticyclones also influence individual hurricanes. Thus a
hurricane passing west over Havana, will go farther west if a vigorous
"high" is spreading southeast over the Gulf States. And when this "high"
passes seaward, the hurricane will work around the southwest quadrant of
the "high," recurving and moving northeast.
STORM RENDEZVOUS
Altho storms originate or are first detected in nine different sections,
it is a fact worth mentioning that they all leave the United States in
the vicinity of New England or Nova Scotia. Some of the southern
depressions starting near the coast, pass to sea south of New York, but
in general an observer standing on Plymouth Rock can virtually encompass
within a radius of 500 kilometres, 300 miles, the paths of ninety per
cent of the storms that traverse the country.
Thus a storm that originates in Texas (7) will probably pass close to
Cape Cod. Likewise, types (3) and (5); while the other types may pass a
little to the north or south. See Chart, Paths of Storms.
STORM PATHS
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