1. Hurricanes and Tornadoes
Severe Weather
Hurricanes and Tornadoes

2. Tornadoes
Tornadoes are a violently whirling column of air, usually seen as a funnel-shaped cloud extending from the base if a thunderhead

3. Tornadoes Tornadoes May be 3m to 3km across
Tornado Alley runs from Texas to Michigan
US averages more than 800 a year
Usually last a few minutes
Very destructive
Winds can be more
than 400 km/h

4. Average tornado frequency by month of year 2003-2005

6. Fujita Scale SCALE WIND ESTIMATE (MPH) TYPICAL DAMAGE F0 < 73
Light damage. Some damage to chimneys; branches broken off trees; shallow-rooted trees pushed over; sign boards damaged. F1
73-112
Moderate damage. Peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos blown off roads. F2
Considerable damage. Roofs torn off frame houses; mobile homes demolished; boxcars overturned; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground. F3
Severe damage. Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted; heavy cars lifted off the ground and thrown. F4
Devastating damage. Well-constructed houses leveled; structures with weak foundations blown away some distance; cars thrown and large missiles generated. F5
Incredible damage. Strong frame houses leveled off foundations and swept away; automobile-sized missiles fly through the air in excess of 100 meters (109 yds); trees debarked; incredible phenomena will occur.

7. Hurricanes
Hurricanes need warm tropical oceans, moisture and light winds above them.
If the right conditions last long enough, a hurricane can produce violent winds, incredible waves, torrential rains and floods.
Also called Typhoons or Cyclones

12. Stages of Development Strong Storm Depression Tropical Storm Hurricane

13. Saffir-Simpson Hurricane Damage-Potential Scale
Scale Number
Category
Central Pressure
mb inches
Wind Speeds
mi/hr knots
Storm Surge
feet meters
Observed Damage 1
>=980
>=28.94
74-95
64-82
4-5
~1.5
some damage to trees, shrubbery, and unanchored mobile homes 2
96-110
83-95
6-8 ~
major damage to mobile homes; damage buildings' roofs, and blow trees down 3
96-113
9-12 ~
destroy mobile homes; blow down large trees; damage small buildings 4
13-18 ~
completely destroy mobile homes; lower floors of structures near shore are susceptible to flooding 5
<"920"
<"27.17"
>"155"
>"135"
>"18"
>"5.5"
extensive damage to homes and industrial buildings; blow away small buildings; lower floors of structures within 500 meters of shore and less than 4.5 m (15 ft) above sea level are damaged