Page 38 - CCPS Monograph - Natural Hazards

Force Speed Description Specifications for use at sea
kph (mph) knots Specifications for use on land
9 75.6-86.9 41-47 Severe Gale High waves. Dense streaks of foam along the
(47-54) direction of the wind. Crests of waves begin to
topple, tumble and roll over. Spray may affect
visibility
Slight structural damage occurs (chimney-pots and
slates removed)
10 88.5-101.4 48-55 Storm Very high waves with long overhanging crests. The
(55-63) resulting foam, in great patches, is blown in dense
white streaks along the direction of the wind. On
the whole the surface of the sea takes on a white
appearance. The tumbling of the sea becomes
heavy and shock-like. Visibility affected.
Seldom experienced inland; trees uprooted;
considerable structural damage occurs.
11 103-115.9 56-63 Violent Exceptionally high waves (small and medium-size
(64-72) Storm ships might be for a time lost to view behind the
waves). The sea is completely covered with long
white patches of foam lying along the direction of
the wind. Everywhere the edges of the wave crests
are blown into froth. Visibility affected.
Very rarely experienced; accompanied by wide-
spread damage.
12 115.9-133.6 64-71 Hurricane The air is filled with foam and spray. Sea
(72-83) completely white with driving spray; visibility very
seriously affected.
see Saffir-Simpson Hurricane Wind Scale

The Fujita Tornado Damage Scale categorizes a tornado based on estimated wind speed. It is no longer
used in the U.S. (SPC 2019)

Table G.2 Fujita Tornado Damage Scale (adapted from SPC 2019)

Scale Wind Estimate Typical Damage
kph(mph)
F0 < 117.5 (73) Light damage. Some damage to chimneys; branches broken off
trees; shallow-rooted trees pushed over; sign boards damaged.
F1 117.5-180.2 Moderate damage. Peels surface off roofs; mobile homes pushed
(73-112) off foundations or overturned; moving autos blown off roads.
F2 181.9-252.7 Considerable damage. Roofs torn off frame houses; mobile
(113-157) homes demolished; boxcars overturned; large trees snapped or
uprooted; light-object missiles generated; cars lifted off ground.
F3 254.3-331.5 Severe damage. Roofs and some walls torn off well-constructed
(158-206) houses; trains overturned; most trees in forest uprooted; heavy
cars lifted off the ground and thrown.

Assessment of and planning for natural hazards 35

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