Severe Weather

Hurricanes and Tornadoes

Tornadoes

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

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

Average tornado frequency by

month of year 2003-2005

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 113-157Considerable 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 158-206Severe 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 207-260 Devastating damage. Well-constructed houses leveled; structures with weak foundations blown away some distance; cars thrown and large missiles generated.

F5 261-318Incredible 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.

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

Stages of Development

Strong Storm Depression Tropical Storm Hurricane

Saffir-Simpson Hurricane Damage-Potential Scale

Scale Number

Category

Central Pressure

mbinches

Wind Speeds

mi/hrknots

Storm Surge

feetmeters

ObservedDamage

1 >=980 >=28.94

74-95 64-82

4-5 ~1.5

some damage to trees, shrubbery, and unanchored mobile homes

2 965-979 28.50-28.91

96-110 83-95

6-8 ~2.0-2.5

major damage to mobile homes; damage buildings' roofs, and blow trees down

3 945-964 27.91-28.47

111-130 96-113

9-12 ~2.5-4.0

destroy mobile homes; blow down large trees; damage small buildings

4 920-944 27.17-27.88

131-155 114-135

13-18 ~4.0-5.5

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