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Hurricane Basics
Tornadoes
Hurricans vs. Tornadoes vs. You
Hurricane Basics
The
practice of naming hurricanes began early in the 20th century when an Australian weather forecaster decided to insult politicians
he didn't like by naming devastating tropical storms after them.
According to the National Hurricane Center, the word
"hurricane" comes from the name "Hurican," the Caribbean god of evil.
Hurricanes are formed from simple thunderstorms. However, these thunderstorms
can only grow to hurricane strength with cooperation from both the ocean and the atmosphere. Hurricanes are born over tropical
oceans when the water is warmer than about 80 degrees. The heat and moisture from this warm water is ultimately the source
of energy for hurricanes. The winds from these storms exceed 74 mph and blow counter clockwise about their centers in the
northern hemisphere and clockwise in the southern hemisphere. Howling winds around the hurricane's eye push water along, tending
to pile it up. In the deep ocean, this dome of water, called a storm surge, sinks and harmlessly flows away. But as a storm
nears land, the rising sea floor blocks the building water's escape and it comes ashore as a deadly storm surge. An
intense hurricane can send a dome of water more than 18 feet deep ashore as a storm hits land.
Hurricanes will weaken
rapidly when they travel over land or colder ocean waters -- locations where their heat and/or moisture sources do not exist.
A
hurricane watch is issued when hurricane conditions are possible within 24 to 36 hours. A hurricane warning is issued when
hurricane conditions (winds of 74 mph or greater, or dangerously high water and rough seas) are expected in 24 hours or less.
Why
do they name hurricanes?
Tropical storms and hurricanes are given names to avoid confusion when more than one
storm is being followed at the same time. A storm is named when it reaches tropical storm strength with winds of 39 mph.
Forecasters began using names in 1950. In that year and in 1951, names were from the international phonetic alphabet in use
at the time - Able, Baker, Charlie, etc. Female, English-language names were used beginning in 1953.
What are the main parts of a hurricane?
Once a hurricane
forms, it has three main parts: Eye - the low pressure, calm center of circulation. Eye wall - area around the eye with the
fastest, most violent winds. Rain bands - bands of thunderstorms circulating outward from the eye that are part of the evaporation/condensation
cycle that feeds the storm
How large is a hurricane?
Hurricanes vary widely in physical size. Some
storms are very compact and have only a few trailing bands of wind and rain behind them. Other storms are looser, so the bands
of wind and rain spread out over hundreds or thousands of miles. Hurricane Floyd, which hit the eastern United States in September
1999, was felt from the Caribbean islands to New England.
Is one side of a hurricane more dangerous than the
other?
Absolutely -- The right side of a hurricane packs more punch because the wind speed and the hurricane speed-of-motion
are complimentary there. On the left side, the hurricane's speed of motion subtracts from the wind speed.
Are
you generally safer from a hurricane if you're inland?
Not necessarily -- While the combination of winds, rain
and flooding can level a coastal town, they can also cause significant damage to cities far from the coast. In 1996, Hurricane
Fran swept 150 miles (241 km) inland to hit Raleigh, N.C. Tens of thousands of homes were damaged or destroyed, millions of
trees fell, power was out for weeks in some areas and the total damage was measured in the billions of dollars.
What is the difference between a tropical storm and hurricane?
Tropical
storms are classified into four categories according to their degree of organization and maximum sustained wind speed.
Tropical
disturbance, tropical wave -- Unorganized mass of thunderstorms, very little, if any, organized wind circulation.
Tropical
depression -- Has evidence of closed wind circulation around a center with sustained winds from 20-34 knots (23-39 mph).
Tropical
storm -- Maximum sustained winds are from 35-64 knots (40-74 mph). The storm is named once it reaches tropical storm strength.
Hurricane
-- maximum sustained winds exceed 64 knots (74 mph).
Tornadoes
How do these meteorological monsters form? Even the experts aren't sure
of every detail, but they do understand some of the basics.
Tornadoes typically form when a mass of cold, dry air blows
in over a mass of warm, wet air near the ground (a fairly common occurrence on the American plains as cold, dry air moves
in over the Rockies and warm, wet air comes up from the Gulf).
Sometimes an intervening layer of hot, dry air keeps the
two air masses separate--with one over the other, like a big air sandwich, but separate all the same. Yet if this "cap" gets
disturbed or weakens, sunny days are over.
The air near the ground, because it's warmer than the air
around it, can then rise in an "updraft," like a hot-air balloon. And as the warm air rises and cools, the moisture in it
can condense into a storm. In fact, condensation releases latent heat, which can make all that cooling warm air warm again
and cause it to rise even higher and more quickly. A particularly powerful updraft can give birth to a towering 50,000-foot
thunderstorm in just minutes.
Many storms pretty much live by updraft alone. But the
worst and longest lived of the lot also manage to hitch their wagons to "wind shear." Wind shear happens when winds change
speed or direction over a short space. For example, the wind at ground level might be a lot slower than the wind just a few
thousand feet up. Or, it might blow from the southeast, while the winds above blow from the southwest.
These differences can create a horizontal vortex in the
air beneath a storm cloud, with winds that spiral like corkscrews as they advance. And if these horizontal corkscrew winds
enter an updraft, they can get tilted up into it. Pretty soon, the updraft takes on their rotation and becomes a vortex, too--a
vertical corkscrew of rising air starting a few thousand feet up and spanning across miles. Meteorologists call this rotating
updraft a "mesocyclone" and a storm that has one a "supercell." Supercells are maternity wards for tornadoes.
Not every supercell spawns tornadoes, but those that do
typically spawn them below their mesocyclone--often near a cool downdraft full of rain or hail. Scientists know that these
downdrafts play a role in bringing the upward spinning mesocyclone closer to the ground.
But, unfortunately, that's where sure and certain tornado
knowledge ends. Why a huge vertical vortex swirling overhead across miles of sky sometimes gives rise to the pinpoint power
of a tight twister in contact with the ground is still shrouded in the dust and debris of the tornado, waiting for science
and stormchasers to find.
--Michael Himick
KnowledgeNews is brought to you by Every Learner, Inc., an independent
small business dedicated to supporting lifelong learners. Copyright © 2008, Every Learner, Inc. All rights reserved.
Hurricanes vs. Tornadoes vs. You
Nature has a thousand ways to kill you. Wind, earthquake,
volcano, drought, flood, fire--you name the place and choose the form of destruction, and nature has an unequivocal way to
show who's boss.
In North America, warm weather brings disaster by air--by hurricane
and tornado. Tornadoes can strike anytime, but occur most frequently in spring and early summer. Hurricane season picks up
where tornadoes leave off, running June through November. Both are awesome forms of windpower that represent nature at its
fiercest.
But which is meaner? Which is deadlier? Which is the baddest
atmospheric force on Earth? We've matched these two forces head-to-head and broken them down with some scientific facts to
see which is the true king of disaster in the sky.
WIND SPEED
| Tornadoes - Packed into tight,
swirling spirals, the winds of the most powerful (F5) tornadoes can reach speeds approaching 320 miles (515 km) per hour--the
most violent winds on Earth. Just how fast is 320 miles per hour? It's faster than a Formula One race car, faster than many
airplanes can fly, and almost half the speed of sound. At that speed, wind can fling cars across football fields and reduce
the sturdiest house to rubble. The majority of tornadoes, however, rage at less than 200 miles (322 km) per hour. That's still
fast enough to uproot trees and destroy your average mobile home. |
Hurricanes - A stiff breeze
of, say, 30 miles (48 km) per hour will blow your trusty umbrella inside out, sweep the hat off your head, and make it hard
to walk upwind. Now triple that speed, and you've got a hurricane on your hands--a weak one. If you wanted a strong hurricane,
you'd have to whip up sustained winds of over 150 miles (241 km) per hour, with gusts that top 200 miles (322 km) per hour.
At hurricane wind speeds, loose debris becomes a barrage of flying missiles. Even if you could stand up straight in
a hurricane wind, it wouldn't be a good idea. |
Advantage: Tornadoes.
It's all in the numbers. Even
the most severe hurricanes make it only halfway up the tornado intensity scale. There's no wind on Earth stronger than the
wind inside a tornado.
SIZE
| Tornadoes - Tornadoes are relatively
small as atmospheric phenomena go. Funnel width at ground-point usually ranges from a few dozen to several hundred yards across.
Some tornadoes reach more impressive widths--more than a mile (1.6 km) at ground-point. Yet because tornadoes move rapidly
along the ground, they can cause damage over a larger area than their size might suggest. Larger, longer-lived tornadoes can
cut a swath of destruction hundreds of miles long. |
Hurricanes - Hurricanes are
huge; they can cover entire states. One look at a hurricane through a satellite photo shows just how big they can be. The
average hurricane is 200 to 300 miles (322 to 483 km) in diameter, and massive hurricanes can span 700 miles (1,127 km) or
more. The size of a hurricane, however, is not directly related to its wind speed or destructive force. Relatively small ones
can pack an incredible punch, while much larger ones can be relatively mild. |
Advantage: Hurricanes.
Tornadoes may dominate the sky,
but hurricanes swallow it whole.
FREQUENCY AND RANGE
|
Tornadoes - Tornadoes tend to occur over flat terrain,
but can travel across mountains and form over water. In 1997, a tornado even passed through the heart of downtown Miami. Although
they're found in places like India, Europe, and Australia, tornadoes are most common--and most powerful--in the United States.
Tornadoes can form year-round, but most occur in a "tornado season" of March through May and through the summer in more northern
states. A typical year will see close to 800 tornado reports in the U.S. and a higher number worldwide.
Advantage: Tornadoes.
What they lack in size, they more
than Take up for in frequency, with some years Having 100 times as many reported tornadoes as hurricanes. And they can get
around the country, too. |
Hurricanes - Because they require
the tropical ocean to maintain their intensity, hurricanes quickly lose their strength when they make landfall or move into
cooler climates. This greatly limits the number of places they can strike. The same factors that spawn hurricanes also limit
their frequency. Like tornadoes, hurricanes tend to strike in season, which in the Atlantic is from June through November.
On average, only a dozen hurricanes a year are spawned there, and many of those never strike populated areas.
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DAMAGE
| Tornadoes - Tornadoes pack
quite a wallop, and when they strike near populated areas, the damage can be severe. Most damage is localized and random.
Tornadoes are notorious for destroying houses on one side of the street while leaving those on the other untouched. The biggest
tornado outbreak in the last century--the "Super Outbreak" of April 3-4, 1974--spawned 148 tornadoes across 13 states and
caused damage in excess of $600 million, $100 million of which resulted from a massive tornado that destroyed half the town
of Xenia, Ohio. |
Hurricanes
- Because of their longevity and immense size, hurricanes can wreak tremendous havoc. The combined effects of wind, rain,
and surf can destroy homes, erode seashores, and flood entire cities. Luckily, most hurricanes spend the majority of their
lives in the open ocean. How much damage a hurricane does is determined as much by when, where, and how it strikes coastal
areas as by the magnitude of the storm itself. When Hurricane Andrew struck both south Florida and Louisiana in 1992, it caused
total damage estimated at $36 billion. |
Advantage: Hurricanes.
Tornadoes pack a solid punch,
but hurricanes deliver a knockout combination of wind and water that tornadoes simply cannot match.
DEATHS
| Tornadoes
- Despite greatly improved weather tracking and warning systems, tornadoes still kill an average of 100 people in the United
States each year. Although they can lift humans into the air and hurl them long distances, flying debris and collapsing buildings
cause most deaths. The worst event on record is the Great Tri-State Tornado of March 18, 1925, a mile-wide monster that tore
across 219 miles (352 km) of Missouri, Illinois, and Indiana, killing 695 people, injuring 2,207, and destroying more than
15,000 homes. |
Hurricanes
- Improved weather tracking and warning systems have greatly reduced the number of deaths caused by hurricanes. The 1928 hurricane
that struck Lake Okeechobee in Florida killed 1,836 people. Estimates from earlier storms point to several that killed even
more. Even with modern satellite tracking and early evacuation plans, Hurricane Floyd caused 56 deaths in 1999. And not every
place has such modern tools. In 1991, a typhoon (as hurricanes are called in the western Pacific and Indian oceans) struck
low-lying sections of Bangladesh and killed almost 140,000 people. |
Advantage: Hurricanes.
Hurricanes kill more, especially
worldwide, even if they do it less often than tornadoes. (Yet neither storm comes close to nature's worst killers: flooding
and drought.)
POWER
| Tornadoes - Yard for yard,
tornadoes pack the most destructive force of any atmospheric phenomenon, possessing a pinpoint violence unmatched by any other
force of nature. In fact, a good-sized twister releases energy at a rate equal to that of two large nuclear reactors. Don't
be too impressed, though. The "supercell" thunderstorms that spawn tornadoes typically have a total energy output thousands
of times greater than that. |
Hurricanes
- The sheer size of a hurricane allows it to unleash massive amounts of destructive power on anything unfortunate enough to
be engulfed by it. And unlike tornadoes, which rarely last for more than an hour, a hurricane can rage for days. All of that
adds up to staggering energy levels. By some calculations, a typical hurricane generates power at a rate equal to that of
half of the electrical production of the entire world at any given time. |
Advantage: Hurricanes.
Even though tornadoes
produce an impressive display of ground-churning power, they lack hurricanes' size and stamina. If that's not enough to convince
you, consider this: Hurricanes are so powerful that they can spin off tornadoes of their own.
INTANGIBLES
| Tornadoes -
In spite of their destructiveness, tornadoes fascinate. Every year, hundreds of people go storm-chasing across the countryside
in an effort to measure, document, or simply witness tornadoes' breathtaking power. For whatever reason, the sight of a funnel
cloud in the sky often sends folks running for their cameras before they run for their lives. |
Hurricanes - Though they certainly
goose the Weather Channel's ratings, hurricanes don't have the cinematic, visual appeal of tornadoes, probably because they're
just too large to be seen in their entirety. It wasn't until humans could look down on these storms from space that their
magnitude could be appreciated. The experience of being in one, however, leaves little to the imagination. |
Advantage: Tornadoes.
They've got style, they're quirky,
and they're quite photogenic. All they need now is an agent. In fact, the movie Twister grabbed $242 million in box office
receipts in 1996 (though U.S. tornadoes caused more than $716 million in estimated damage the same year).
AND THE WINNER IS....HURRICANES
Both hurricanes and tornadoes are amazing, they're both deadly, and they're
both destructive. But in this case, size does matter. Tornadoes may be more visually spectacular, and evoke more popular excitement
and interest, but the sheer magnitude and power of the hurricane is unmatched among nature's skyborne forces.
Christopher Call
Copyright
2004, KnowledgeNews. All rights reserved.
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