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Hi, my name is Rodney from the Tampa Bay National Weather Service office.
Today we will cover tornadoes and thunderstorms, the next topic for severe weather awareness
week 2014. Let’s get started. Tornadoes are one of the most destructive
weather forces across the country and can occur anytime during the year, day or night.
An average of 1,200 tornadoes occur each year and cause 86 fatalities and 1,500 injuries
nationwide. In 2013 there were 36 tornadoes reported statewide with 14 of those occurring
here in west central and southwest Florida. Tornadoes are classified using the Enhanced
Fujita scale which ranks storms from EF0 to EF5. EF0 and EF1 are very typical here in
Florida. Last year, all 14 tornadoes that were reported in west central and southwest
Florida were either EF0 or EF1. EF2 and 3 are rare in West central Florida. Most can’t
forget the EF-3 that went through parts of Sumter and Lake Counties in 2007. EF4 are
very rare in west central Florida and haven’t been recorded in the last few decades. EF5
is extremely rare in west central Florida and haven't been reported in recent history.
No one was injured or killed in Florida during last year’s tornadoes.
There are 3 different scenarios where tornadoes form in Florida. Frontal System Tornadoes
occur mostly in the late winter and spring...forming along a preceding squall line. Sea Breeze
or Boundary Collisions Tornadoes are the most common and happen mainly in the late spring
and summer. Tropical Cyclone Band Tornadoes form on outer bands of land falling tropical
cyclones. In general, tornadoes form when rapidly rising
air in a thunderstorm updraft combines with an increase in wind speed or a change in wind
direction known as shear. The larger the shear, the greater the rotation and thus the better
chance a tornado will form. Here are some safety rules. If a tornado warning
has been issued for your area, seek shelter immediately. If you are inside, seek shelter
in an underground shelter, basement or the innermost room on the lowest level away from
windows. If you do not have time to get to the lowest level, get under a bed. At school,
get under your desk. In Open Country - Seek a nearby shelter, if time permits. If not,
lie flat in the nearest depression, ditch or culvert. Cover your head with your arms.
Abandon mobile homes and go to a firmly built shelter. Vehicles are extremely dangerous
in a tornado. If the tornado is visible, far away, and the traffic is light, you may be
able to drive out of its path by moving at right angles to the tornado. Otherwise, park
the car as quickly and safely as possible -- out of the traffic lanes. Get out and seek
shelter in a sturdy building. Avoid seeking shelter under bridges, which may cause deadly
traffic hazards while offering little protection against flying debris.
For the second half of today’s topic we’ll focus on Thunderstorms. Thunderstorms are
almost a daily occurrence in Florida between June and September mainly because of the sea
breeze. This figure shows the average number of thunderstorm days each year throughout
the U.S. So we can see that areas from near Tampa Bay south to Lee county have to deal
with thunderstorms 100 days a year. All thunderstorms are dangerous with lightning, heavy rainfall
and gusty winds, but today we’re going to focus on the most dangerous type, the severe
thunderstorm. One definition of a severe thunderstorm is
a thunderstorm that has wind gusts exceeding 58 mph. These winds can be classified as either
straight line winds or downburst winds. The damage created by these winds can be equivalent
to that seen from a tornado and can level large areas of forest and housing developments.
The other criteria to be classified as a severe thunderstorm is hail of 1 inch or greater
in diameter. Hail is more common in late spring / early summer, but can occur any time of
year. Hail is very destructive for property and crops causing over 1 billion dollar in
damage each year. If you are caught outside in a hail storm, seek shelter immediately
as hail can cause serious injuries. Remember to always plan ahead and check the
forecast at weather.gov/tampa. For more tips on tornado and thunderstorm
safety, check these websites. This concludes the topic for today. The next
training topic will be temperature extremes and wild fires.