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Ask the Experts
About :
Hurricanes
Q: Which are more common, hurricanes or earthquakes?
A: The U.S. Geological Survey estimates that there are 500,000
detectable earthquakes in the world each year, with 100,000 of these
strong enough to be felt and 100 of them strong enough to cause damage.
These numbers dwarf the number of hurricanes in the world each year --
according to NASA, about 85 hurricanes, typhoons and tropical cyclones
occur worldwide each year.
It is important to note the differences between hurricanes and
earthquakes hurricanes are a meteorological phenomenon while
earthquakes are geological. Both hurricanes and earthquakes can produce
damage by flooding of coastal areas, but a hurricane's storm surge and a
tsunami associated with an earthquake are entirely different phenomena.
Check out these USA TODAY resource pages about tsunamis and storm surge.
(Answered by meteorologist Bob Swanson, USA TODAY's assistant weather
editor, December 3, 2006)
Q: How warm must ocean water temperatures be to produce a Category 5
hurricane?
A: Sea surface temperatures (SSTs) are only one factor in hurricane
development, so there is no set temperature by which ocean waters must
be to produce a Category 5 storm. Steve Lyons, tropical weather expert
at The Weather Channel, blogged about how SSTs are not all that
important in hurricane development.
One interesting point he makes is that nearly the entire tropical
Atlantic, Caribbean Sea, and Gulf of Mexico are warm enough to produce a
Category 5 hurricane during the peak months of the tropical
season-August, September, and the first half of October. In addition,
the intensification of hurricanes depends not only on SSTs, but on
temperatures up in the atmosphere as well. Air can heat up much more
quickly than water, and a slight increase in air temperature, just like
warmer water, can help strengthen a hurricane.
Finally, wind shear--changes in the atmosphere's winds with height--can
affect a hurricane's development. Less wind shear allows for more rising
air, which is favorable for hurricane development. More wind shear can
cut off a hurricane's top, breaking apart its core circulation.
Learn more about wind shear and how it can tear apart hurricanes on this
USA TODAY resource page.
(Answered by Greg Seroka of USA TODAYs weather staff, August 1, 2006)
Q: Can hurricanes form in the Southern Hemisphere?
A: Hurricanes can, and often do, form in the Southern Hemisphere, where
they're called cyclones. The factors that aid in tropical storm
development, including warm ocean water and low wind shear, are present
in both of the Earth's hemispheres.
Tropical cyclones in the Southern Hemisphere spin in a clockwise
direction, which is opposite to hurricanes in the Northern Hemisphere.
In addition, the Southern Hemisphere typically has about half the number
of hurricanes as the Northern Hemisphere each year.
Since the seasons are opposite in the Southern Hemisphere, the hurricane
season there lasts through the Northern Hemisphere's colder months --
late October through May. The Southern Hemisphere has three major basins
for tropical storm development: the Southwest Indian Ocean, the
Australian Region, and the South Pacific Ocean. The storms primarily
affect Australia and southeastern Africa.
Tropical storms rarely occur in the South Atlantic because of cooler
waters, high wind shear, and the absence of an Intertropical Convergence
Zone -- a constant area of low pressure and thunderstorm activity along
the Earth's equator. In fact, until two years ago, a hurricane-strength
storm had never been never reported in the South Atlantic. Cyclone
Catarina became the first recorded South Atlantic hurricane when it
formed on March 26, 2004.
Check out FAQ's about hurricane science on this USA TODAY resource page.
(Answered by Greg Seroka of USA TODAYs weather staff, June 12, 2006)
Q: How long does hurricane season last?
A: The Atlantic Ocean, Caribbean Sea and Gulf of Mexico hurricane season
runs from June 1 through Nov. 30, but, most hurricanes occur from around
the middle of August through the middle of October.
Q: Do hurricanes only occur near water?
A: Yes, hurricanes form over tropical oceans. They often move away from
the tropics to hit the U.S. and other non-tropical parts of the world.
But, once a hurricane moves over land or cold ocean water it begins to
weaken quickly and dies. A USA TODAY online graphic on why hurricanes
form over warm water explains why.
Q: What do red flags with black squares represent? They always put them
up when there is a hurricane, sometimes there are two or more flags.
A: These flags are usually seen during the hurricane season, especially
on news broadcasts, but most people do not know what they mean. The two
flags you're speaking of are square, red flags and usually measure 36" x
36" with a black square in the middle that measures 12" x 12". When one
of these red flags are hanging, that warns mariners that a storm warning
has been posted. A storm warning means winds between 48-63 knots (55-73
mph) are likely within 24 hours. When two flags are hoisted, one below
the other, this means a hurricane warning is in effect. A hurricane
warning means winds equal or greater than 64 knots (74 mph) are likely
within 24 hours.
Pennants are also used to indicate additional marine advisories. One
pennant indicates a small-craft advisory which alerts mariners that
weather, potentially dangerous to small crafts, is either occurring or
is forecast. Dangerous conditions include rough seas and winds of 18-33
knots (28-28 mph). When two pennants are hoisted, one below the other, a
gale warning is in effect and is issued when winds blow between 34 and
47 knots (39-54 mph).
Q: Do hurricane winds go clockwise or counterclockwise?
A: In the Northern Hemisphere, the winds flow in toward the storm's
center in a counterclockwise direction. The go clockwise in the Southern
Hemisphere. By the way, the storms themselves don't move clockwise or
counterclockwise, just their winds. The storms are pushed by the general
flow of upper-atmosphere winds and can move in any direction.
Q: Are the winds on one side of a hurricane faster than on the other
side?
A: If a hurricane or other tropical cyclone is moving the winds on one
side will be faster than on the opposite side in relation to the ocean
or ground the storm is moving over. In the Northern Hemisphere the
fastest winds will be on the right side, if you are looking in the
direction of the storm's movement. That is, if the hurricane is moving
toward the west, the strongest winds will be on the north side; if it's
moving north, the strongest winds will be on the east side.
It's the opposite in the Southern Hemisphere. (See the question right
above this one for why.)
To see why the winds on the right side of a Northern Hemisphere
hurricane or typhoon are faster than those on the left, imagine the
winds are circling the storm at 100 mph, and the entire storm is moving
forward at 10 mph. With counterclockwise winds of 100 mph added to the
forward speed of 10 mph on the right side, a ship there will be hit by
110 mph winds because the 100 mph winds and forward motion of the storm
are in the same direction.. Another ship, to the left of the storm's
center, where the 10 mph forward motion is subtracted from the 100 mph
wind speed, will feel 90 mph winds.
This was first realize in the 19th century and was one of the first
important advances in understanding tropical cyclones and other storms.
In fact, this knowledge was called the "Law of Storms" in the 19th
century and various scientists wrote books telling ship captions how to
use it to figure out where they were in relation to a storm's center and
which way to go to said away from a storm's strongest winds and highest
waves. This is described in detail in Chapter 2 of Hurricane Watch:
Forecasting the Deadliest Storms on Earth by Dr. Bob Sheets and Jack
Williams, published by Vintage Books, 2001.
Q: What's the difference between a hurricane, a typhoon, and a tropical
cyclone?
A: They are all the same kind of storm, "tropical cyclones." In the
Atlantic Ocean, Caribbean Sea, Gulf of Mexico and east of the
International Date Line in the northern Pacific, they are called
"hurricanes." West of the Date Line in the northern Pacific they are
called "typhoons." In other parts of the world they are just called
"tropical cyclones." Our Tropical cyclone and hurricane glossary has
more information.
Q: How big are most hurricanes and how long do they last?
A: A small hurricane might be 100 miles across while a large one could
be more than 300 miles wide. Some hurricanes have lasted only a few
hours as a hurricane (they were weaker tropical storms and depressions
before and after being hurricanes) while a few have lasted more than two
weeks.
Q: What would happen if two hurricanes hit each other?
A: Hurricanes never run into each other. Sometimes two storms will begin
moving close to one another. When this happens the winds around the
storms begin interfering with one another. Usually this will weaken one
or both storms. Some times the storms begin circling each other. This is
the Fujiwhara effect, which we describe in online text. No matter what
they do, two hurricanes never come together to form a stronger storm.
Q: Why do hurricanes change directions?
A: Winds in the upper atmosphere, especially winds from about 10,000 to
40,000 feet above the ocean and land, steer hurricanes.
Q: When and where do hurricanes strike?
A: In the Atlantic and Eastern Pacific oceans, hurricanes and tropical
storms form and strike during a specific time of year, not year-round.
Find out when this is and how this season varies by clicking on the link
below. The next link lets you glimpse state-by-state into the history of
landfalling hurricanes.
U.S. Hurricane climatology
Q: Do hurricanes ever hit the USA's West Coast? If not, why not?
A: No hurricane is on record as having ever hit the U.S. Pacific Coast.
A USA TODAY graphic has more on why hurricanes stay away from California
and places farther north. Hurricanes, however, do hit Mexico's West
Coast. And, the remnants of tropical storms and hurricanes have affected
California. Click here for more information.
Q: When were names first used for hurricanes? When were men's names
first used?
A: Forecasters begin 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. were used. Female, English-language names
were used beginning in 1953. Alternating male and female names were
first used to name Atlantic Basin hurricanes in 1979. This was also the
first year that French and Spanish names, as well as English, were used.
The USATODAY.com page Why hurricanes are named has more information and
links to lists of names.
Q: How can I find out if there has ever been a hurricane with my name or
any other particular name?
A: Start by going to the USATODAY.com hurricane names page. If you
scroll down to the "Naming basics" headline you'll find a link to "the
list of retired hurricane names," which are storms damaging or deadly
enough that their names are no longer used. If you don't find the name
there, follow the link to the National Hurricane Center's list of names
for the entire world.
If you want to spend some time seeing if the name was used in the past,
go to our hurricane history page and scroll down to the "Archives of
hurricane information" headline. Here you'll find a link to the Unisys
hurricane archives, which has year-by-year listings of every hurricane
in the Atlantic, East Pacific and West Pacific. In the Atlantic, names
of people were first used in 1953. Names started in the eastern Pacific
in 1957. The archives show names for typhoons in the western Pacific all
of the way back to 1945.
Q: What kinds of airplanes are used to fly into hurricanes? Why do
people fly into hurricanes?
A: Currently, the U.S. Air Force Reserve uses WC-130 airplanes and the
National Oceanic and Atmospheric Administration has WP-3 turboprops and
a Gulfstream jet used for hurricane flying. The airplanes collect
detailed information for both hurricane forecasting and scientific
research. The USATODAY.com page Resources: Hurricane hunter airplanes
has links to a lot of information.
Q: How can I find out when the last hurricane hit a particular part of
the U.S. Coast or how many hurricanes have hit and when they hit?
A: The best starting point is to go to the USATODAY.com Hurricane
history page and scroll down to the ribbon that reads, "Hurricane
climatology, averages." The second link, to the NCDC, will help you get
started finding how many storms have hit particular parts of the coast.
Q: Do hurricanes do any good, or are they all bad?
A: Tropical storms and hurricanes often bring rain that can ease or even
end droughts. In fact, tropical storms or hurricanes have ended many
droughts in Texas, and other parts of the world. Hurricane Dolly in
August 1996 is a good example. It caused damage in Mexico, but also
brought badly needed rain to parts of Texas.
All storms, including hurricanes, help do another needed job for the
Earth by helping to maintain the Earth's heat balance. Ocean currents
carry warm water toward the poles and cold water south toward the
tropics, warming polar regions and cooling the tropics. But these
currents do only about 40 percent of the job. Storms, including
hurricanes do the rest. Hurricanes help carry heat away from the
tropics. Other storms both carry cold air toward the tropics and warm
air toward the poles.
Q: The Oregon Coast often has winds in excess of 100 mph. Why are these
storms not reported as hurricanes like those on the east coast?
A: The strong winds that hit the Pacific Coast are from extratropical
storms, not hurricanes, which are tropical cyclones. While 100 mph winds
are strong for an extratropical storm, a 100 mph hurricane is relatively
weak compared with what hurricanes can do. The much greater destruction
hurricanes bring led to the establishment of the National Hurricane
Center and the other special attention given to these storms. The term
"hurricane force winds" causes confusion. While any wind 75 mph or
faster is "hurricane force," such winds don't always come from
hurricanes. USA TODAY online has a file with more information on eastern
Pacific tropical and extratropical storms, including one storm that
began life as a tropical storm but was extratropical when it hit Oregon
with 100 mph plus winds.
Q: Do hurricanes form in the Mediterranean Sea?
A: This answer is from Chris Landsea of NOAA's Hurricane Research
Division in Miami. On rare occasions, tropical cyclones (or storms that
appear to be similar in structure to tropical cyclones) can develop in
the Mediterranean Sea. These have been noted to occur in September 1947,
September 1969, January 1982, September 1983, and, most recently, during
13 to 17 January, 1995. The 1995 storm is featured on Jack Beven's
Mediterranean Hurricane page. Beven is a lead forecaster at the National
Hurricane Center.
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