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Tornadoes

 

WHAT IS A TORNADO?

A tornado is a violent whirlwind that usually develops in association with a severe thunderstorm. However, tornadoes in Florida can form in a variety of ways, and in all seasons. The winds in a tornado can exceed those measured in the most intense hurricanes. Wind speeds in an intense tornado likely rise above 200 miles an hour. These violent winds are what make tornadoes so deadly – they can uproot and snap trees, down power lines, move or pick up cars and trucks, and destroy homes.  In addition, the wind-thrown debris poses a serious hazard to people in the path of a tornado. Tornado survivors, when asked to describe the noise, usually compare it with an approaching freight train or jet aircraft.

Tornadoes come in many shapes, colors, and sizes. However, a typical tornado is visible as a spinning, gray, funnel-shaped cloud extending below the base of a large thunderstorm cloud.  Tornadoes vary greatly in width. Some are skinny, while others are quite wide.  Tornado width can range from just a few dozen yards to over a mile!  Often, a tornado is seen extending straight up and down between the base of the thunderstorm cloud and the ground.  However, some tornadoes may appear tilted, or even twisted. The color of the funnel is usually gray, dark gray, or nearly black. However, sometimes sun, sky, and even dirt can bend light in such ways as to cast tinges of green, yellow, or red on to the funnel. The paths of tornadoes can be very short, or they can extend for many miles.  Not surprisingly, tornado ground speeds range from nearly stationary to over 50 miles per hour.     


Tornado damage on October 19, 2007.

Where and When Do Tornadoes Occur?

Tornadoes have been reported in most of the temperate and tropical regions of the world.  However, there are certain atmospheric ingredients that allow tornado formation come together with great frequency.  These ingredients include:

  1. Wind shear - a turning of the winds with height in the air;

  2. A strong vertical wind called an “updraft”, usually associated with an intense thunderstorm;

  3. A zone of colliding air masses near the surface.

In Florida, these ingredients may come together during any season, and at any time of day, and are associated with a variety of different weather patterns.  Destructive Florida tornadoes often form in families during the dark of night, east of a developing storm system over the Gulf of Mexico.

Tornadoes occasionally develop in the afternoon beneath the huge thunderstorms, which can erupt along a collision of summer-time sea breezes. This commonly occurs in the areas around Fort Myers, Tampa Bay, Lake Okeechobee, and along the Atlantic coast.  Such an event occurred in August 2003 when two tornadoes damaged portions of metropolitan Palm Beach County. 

Tornadoes also occur during the warm season within the spiral rainbands of landfalling hurricanes and tropical storms, as witnessed in the Panhandle during Hurricane Ivan in 2004 or in the Florida Keys during Tropical Storm Mitch in 1998. 

 


A waterspout on the St. Johns River
in Jacksonville on July 26, 2009.

Waterspouts

A waterspout is a tornado over water.  Florida waterspouts come in all shapes, sizes, and intensities.  Many of the waterspouts which develop off the Florida coast during the peak summer months are not as intense as those which form during the winter or spring months, or those which develop within hurricane or tropical storm rainbands.  This typically slower-moving and weaker waterspout develops quickly beneath a rapidly building cumulus cloud line, just at the hint of rain.  These spouts are quite common over the waters along the Florida Keys, the lagoons and rivers along the Florida Treasure coast, and Tampa Bay.  Waterspout winds can reach and exceed 40-90 mph, strong enough to swamp or capsize a small watercraft.  All waterspouts pose a threat to boater safety, and should be avoided.

 

 

Tornadoes Prediction, Detection and Warnings

Your local National Weather Service forecasters serve the state of Florida from offices located in Jacksonville, Melbourne, Miami, Key West, Ruskin (Tampa Bay), Tallahassee, and Mobile, Alabama, and maintain a weather watch around the clock.  When the potential for a tornado increases, thunderstorms are closely monitored using Doppler radar. In addition, networks of specially trained volunteers called “SKYWARN spotters” serve as “eyes and ears” in the field, providing valuable “ground truth” information.

Tornado Safety Actions – Be Weather-Ready!

Tornado safety begins with a plan. Know what you would do if a Tornado Watch or a Tornado Warning is in effect for your community.  A Tornado Watch is a “heads up” issued when conditions are favorable for tornadoes over a particular region. A Tornado Warning means, “take cover now!” and is issued for your area when a tornado is expected or imminent. Consider purchasing a NOAA All-Hazards Weather Radio to alert you of imminent severe weather in your community. 

The number one wind safety rule is to get as many walls as possible between you and the outside world, so the debris in the wind cannot reach you. It is not the wind that kills and injures, but the debris in the wind.

 

Remember the difference!

A Watch is a ‘heads-up’. It means pay attention. Make sure you know where to go for shelter if you need to make a rapid decision. Be sure you have a way to be alerted or awakened if a warning is issued.
A Warning means take cover now! The threat is ongoing or is forecast to strike soon! Get in, and get down!

More information about tornado hazards and what you can do to protect yourself and others can be found at http://www.nssl.noaa.gov/edu/safety/tornadoguide.html or http://www.floridadisaster.org.

 

How Does the Enhanced FUJITA Scale Work?

The Enhanced Fujita Scale (EF Scale) uses actual damage to estimate a tornado’s wind speed. Tornadoes are classified according to the damage they cause, on the Fujita Scale. This scale was named after its creator, Dr. Theodore Fujita. The EF Scale is to be used with caution. Tornado wind speeds are still largely unknown, and the wind speeds on the EF Scale never have been scientifically tested and proven. Winds of different speeds may cause the same damage depending on how well-built a structure is, wind direction, wind duration, battering by flying debris and various other factors.

Fujita Tornado Damage Scale
Developed in 1971 by T. Theodore Fujita of the University of Chicago
SCALE MPH TYPICAL DAMAGE
EF0 65-85 (mph) Gale Tornado
Some damage to chimneys. Tree branches broken off. Shallow rooted trees uprooted.
EF1 86-110 (mph) Moderate Tornado
Peels surface off roofs. Mobile homes overturned. Moving autos pushed off roads.
EF2 111-135 (mph) Significant Tornado
Considerable damage. Roofs torn off frame houses. Large trees snapped or uprooted. Light-object projectiles generated.
EF3 136-165 (mph) Severe Tornado
Severe damage. Roofs and some walls torn off well-constructed homes. Most trees in forests uprooted. Heavy cars lifted off ground.
EF4 166-200 (mph) Devastating Tornado
Well-constructed houses leveled. Structures blown off weak foundations. Cars thrown and large projectiles generated.
EF5 200+ (mph) Incredible Tornado
Strong frame houses lifted off foundations and disintegrated. Automobile-sized projectiles fly through the air in excess of 100 mph. Trees debarked.

The Enhanced Fujita Scale (EF-Scale) replaced the Fujita Scale (F-Scale) on February 1, 2007.

The original Fujita Scale (F-Scale), created by meteorology professor Doctor Theodore Fujita, was used by the National Weather Service from 1971 to 2006 to rate the strength of tornadoes. His scale used tornado damage to estimate tornado wind speeds. However, Dr. Fujita's scale did not consider how well a structure was built or flying debris around the tornado. As a result, some tornado wind speeds were reported higher than they actually were.

The Enhanced F-Scale (EF-Scale) was created by meteorologists and wind engineers to make estimating tornado winds more accurate. The EF-Scale looks at 28 different types of wind damage to trees, homes, power lines, businesses and skyscrapers. The original F-Scale did not take all of these details into account.

The EF-Scale will usually result in a lower wind speed than the F-Scale if the damage is similar. For example, an EF-Scale F3 tornado would have wind speeds between 136 and 165 miles per hour (mph), while the old F-Scale F3 tornado would have wind speeds between 162 and 209 mph. The wind speeds needed to cause F3 damage are not as high as once thought. More information can be found at http://www.spc.noaa.gov/faq/tornado/ef-scale.html.

 

 



Homes
  • When a tornado watch is issued, be prepared to take action.
  • When a tornado warning is issued, or a tornado is imminent, move to a small interior room away from windows.
  • Consider constructing a tornado safe room in or adjacent to your home.
Open Country
  • Seek a nearby shelter if time permits.
  • If not, lie flat in the nearest depression, a ditch or culvert. Cover your head with your arms.
Vehicles
  • Abandon your vehicle and seek refuge in a building or, as a last resort, a ditch.
  • Do not try to outrun a tornado.
Offices, Hotels and Condominiums
  • When action is required, take shelter in an interior hallway on a lower floor, closet or small room.
  • As a last resort, get under heavy furniture, away from windows.
Manufactured and Mobile Homes
  • Have a plan of where to go during a tornado threata nearby pre-identified safe structure within walking distance.
  • When a tornado watch is issued, be prepared to take action.

Update

January 19, 2012 11:03