From: Florida's Hurricane History, second edition
By Jay Barnes
ISBN: 978-0-8078-3036-0, $39.95 hardcover; ISBN: 978-0-8078-5809-7, $24.95 paperback
University of North Carolina Press. Published May 2007
As old as the oceans themselves, hurricanes are born each year from the heat
of the Tropics. They begin as innocent thunderclouds and evolve into massive
storms with violent winds and torrential rains. They may live for days or for
weeks, and most die off harmlessly over cooler waters. Some track dangerously
close to land before veering away just beyond the shoreline. Occasionally these
storms make landfall with a violent blast of wind, rain, and tide. Other storm
systems may be larger and tornadoes sometimes pack more violent winds, but
nothing in our atmosphere can match the broad-scale destructive force of hurricanes.
These seasonal cyclones and their counterparts around the globe are
the greatest storms on earth, killing more people worldwide than all other
storms combined.
They are called hurricanes in the Western Hemisphere, a term probably derived
from “Hurukan,” the name of the Mayan storm god, and other similar
native Caribbean words translated as “evil spirit” or “big wind.” In the western
Pacific, they are known as typhoons, and in the Indian Ocean, they are called
cyclones. These terms all describe the same phenomena—cyclonic storms that
form in all tropical oceans except the South Atlantic and Southeast Pacific.
As the intense rays of the summer sun warm the ocean’s surface, evaporation
and conduction transfer enormous amounts of heat and moisture into the atmosphere,
fueling the birth of tropical cyclones. Warm vapors rise, cool, and
condense, forming billowing clouds, scattered showers, and thunderstorms.
Newborn thunderstorms grow and multiply, many produced in passing tropical
waves—low-pressure troughs that drift westward through equatorial waters.
Some waves become tropical depressions as thunderheads build, pressures drop,
and low-level circulation develops. If conditions are favorable, a depression can
intensify until sustained winds reach 39 mph, at which time it becomes a tropical
storm. Once the tropical storm’s rotation becomes well organized, its central
pressure falls, and sustained winds reach 74 mph, a hurricane is born.
Satellite images of fledgling tropical systems give meteorologists the opportunity
to watch these storms develop over a period of hours and days. Forecasters
look for signs of rotation and organized convection in emerging storms,
which indicate the potential for strengthening. The earth’s spin produces the
Coriolis effect, which causes winds within a tropical depression to spiral around
the central low pressure. These winds encounter surface friction that causes
them to spiral inward, helping to intensify the storm by bringing warm, moist
air to recharge the growing thunderstorms. Once the circulation completely
surrounds the center, a relatively calm eye sometimes develops, from which
massive rainbands spiral outward for many miles. The storm’s most intense
winds are found at the edge of the eye in the eyewall. It is usually here that the
hurricane delivers its greatest destruction.
In order for a tropical storm to develop and intensify, it must encounter
minimal vertical shear. Shearing winds, like those produced by upper-level lows,
sometimes blow the tops off developing storms, never allowing a convective
“chimney” to form. In the absence of strong shear, storms can more readily
strengthen. Once a storm becomes a well-developed hurricane, it may cover
thousands of square miles as it tracks across the ocean’s surface. Whether it
maintains its strength and direction or stalls and dissipates depends on the effects
of the atmosphere that surrounds it. Rivers of air push and steer the hurricane,
while nearby low-pressure troughs and high-pressure domes can either
draw or block the storm. High-altitude steering currents and low-level trade
winds influence the hurricane’s course, and the combination of these forces
can produce erratic storm tracks. Some hurricanes have been known to track in
a loop (like Hurricane Easy in September 1950). Others appear to wobble, much
like a child’s top spinning precariously across a table.
As long as they remain over warm water, tropical cyclones can strengthen. To
intensify, they need a good supply of fuel—the heat and moisture available in
the atmosphere at sea. As they move over relatively cooler waters or over land,
they lose their source of energy and begin to weaken. Nevertheless, hurricanes
and tropical storms can sometimes track deep inland before fully dissipating.
Some, like Opal in 1995 and Ivan in 2004, can cause extensive damage to areas
many miles from the coast. In Florida many hurricanes that make landfall on
one coast cross the peninsula only to reenter the warm waters on the other side,
where they sometimes regain their strength. Like Donna in 1960 and Andrew in
1992, many of Florida’s most infamous storms have swept the state from coast
to coast before eventually making landfall a second time in another state.
During the long, hot days of late summer, ocean temperatures reach their
peak, and tropical storm activity increases. August, September, and October
are the prime months for hurricanes in the Atlantic, but the official hurricane
season runs from June 1 through November 30. Hurricanes have been documented
in the Atlantic in the months before and after the official season, but
the majority of tropical cyclones occur from June through November. The earliest
hurricane ever to strike the U.S. coast was Alma, which hit the Florida
Panhandle as a minimal hurricane on June 9, 1966. The latest hurricane known
to make landfall in the United States, an unnamed storm on November 30,
1925, also struck Florida, near Tampa.
Although Andrew came in August, September is clearly the most dangerous
month for tropical cyclones in Florida. Over 60 percent of the major hurricanes
to strike the state in the twentieth century occurred during this month,
many within the first two weeks. Most of Florida’s worst hurricane disasters
occurred in September, including the great hurricanes of 1926, 1928, 1935, 1945,
and 1947, as well as Donna in 1960, Betsy in 1965, Eloise in 1975, and Ivan in
2004.
Early-season hurricanes that strike Florida most often make landfall on the
Gulf coast. In August and September, Cape Verde—type storms (born from African
waves near the Cape Verde Islands) form in the eastern Atlantic and track toward
the west. These hurricanes are often very severe and have battered Florida’s
Atlantic coast many times through the years. Hurricanes affecting Florida early
or late in the season often emerge from the western Caribbean and the Gulf
of Mexico and can strike either the Gulf or the southeastern coast. During the
winter months, severe and damaging storms called nor’easters sometimes brew
off Florida’s coasts, but these storms are not true hurricanes. They are known
to meteorologists as extratropical cyclones, and they lack the warm central air
mass and well-defined eye of a hurricane.
Even so, nor’easters have been known to cause major destruction. The Ash
Wednesday storm of March 1962 was perhaps the biggest Atlantic extratropical
storm of the twentieth century. For three long days, this nor’easter stalled off
the Atlantic coast, during a time of high spring tides and full moon, and battered
the coastline from Florida to New England. Florida experienced considerable
damage, but the storm’s worst floods and most concentrated destruction
occurred from North Carolina to New York. The Lincoln’s Birthday storm of
1973 and the March superstorm of 1993 are two other notable nor’easters of recent
years. Residents along Florida’s east coast regularly experience nor’easters
and other winter storms and sometimes endure coastal flooding and severe
beach erosion from them.
Each year, about sixty tropical waves form in the Atlantic, Caribbean, and
Gulf of Mexico. On average, only about ten reach tropical storm intensity, and
only about six become hurricanes. The U.S. coastline will be struck by an average
of more than three hurricanes every two years, anywhere from Texas to
Maine. Almost 40 percent of all U.S. hurricanes hit Florida. According to the
statistical averages, hurricanes battered Florida in about three out of every
five years during the twentieth century. But statistics can be misleading in any
attempt to determine what to expect in the future. And few hurricane seasons
seem average in Florida.