Figure16.30: Ahypotheticalmid-latitudecycloneaffectingtheUnitedKingdom. Thearrows
indicate the wind direction and its relative temperature;Lsymbolizes the low pressure area.
Notice the warm, cold, and occluded fronts. ( 21 )
the Northern Hemisphere and clockwise in the Southern Hemisphere. Since the rising air is
moist, rain or snow falls.
Mid-latitude cyclones form in winter in the mid-latitudes and move eastward with the west-
erly winds. These two to five day storms can reach 1,000 to 2500 km (625 to 1,600 miles ) in
diameter and produce winds up to 125 km (75 miles) per hour. Like tropical cyclones, they
can cause extensive beach erosion and flooding.
Mid-latitude cyclones are especially fierce in the mid-Atlantic and New England states where
they are callednor’easters, because they come from the northeast. About 30 nor’easters
strike the region each year. Most do little harm, but some are deadly. The typical weather
pattern of a nor’easter is familiar to anyone who has lived in this region. First, heavy snow
and ice cover the ground. Then, air temperature warms and rain falls. The rain hits the
frozen ground and freezes, cloaking everything in ice (Figure16.31).
Hurricanes
Tropical cyclones have many names. They are calledhurricanesin the North Atlantic and
eastern Pacific oceans,typhoonsin the western Pacific Ocean,tropical cyclonesin the Indian
Ocean, andwilli-willi’sin the waters near Australia (Figure16.32). By any name, they are
the most damaging storms on Earth.
For a hurricane to form, sea surface temperature must be 28oC (82oF) or higher. Hurricanes