Transcript hurricanes_and_tornadoes

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.
113-157
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
158-206
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
207-260
Devastating damage. Well-constructed houses leveled; structures with weak
foundations blown away some distance; cars thrown and large missiles generated.
261-318
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.
F2
F5
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
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Stages of Development

 Strong Storm
 Depression
 Tropical Storm
 Hurricane
Saffir-Simpson Hurricane Damage-Potential Scale
Scale Number
Category
Central Pressure
mb
inches
Wind Speeds
mi/hr
knots
Storm Surge
Observed
Damage
feet
meters
1
>=980
>=28.94
74-95
64-82
4-5
~1.5
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
>"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
5
<"920"
<"27.17"
>"155"
>"135"
some damage to trees, shrubbery, and unanchored
mobile homes