The Handy Math Answer Book

3 111-130 mph 964-945 mb Surges are 9 to 12 feet above normal; small

(178-209 kph; homes and utility buildings receive structural

96-113 knots) damage; leaves blown off trees and some large

trees blown over; mobile homes destroyed;

coastal and low-lying areas flood 3 to 5 hours

before center of hurricane reaches shore;

evacuations of low-lying areas may be needed

4 131-155 mph 944-920 mb Waters surge 13 to 18 feet above normal; small

(210-249 kph; homes may lose roofs; trees and signs blown

114-134 knots) down; mobile homes destroyed; many doors and

windows destroyed; low-lying and coastal areas

flood 3 to 5 hours before center of hurricane

reaches shore; all terrain lower than 10 feet above

sea level should be evacuated before flooding;

homes as far as 6 miles inland can be affected

5 >155 mph <920 mb Waters surge more than 18 feet above normal

(>249 kph; levels; many house and commercial buildings

>135 knots) lose their roofs; some small buildings and small

utility structures completely destroyed; all

vegetation leveled; major damage to lower

levels of homes and other buildings that are less

than 15 feet above sea level and within 500

yards of shoreline; massive evacuations required

The Fujita-Pearson Tornado Intensity Scale(or “F-Scale”) is used to measure tor-
nado wind speeds. It was developed in 1971 and named after Tetsuya Theodore Fujita
(1920–1998) of the University of Chicago and Allan Pearson, who was then head of the
National Severe Storms Forecast Center in Kansas City. It was Fujita who came up
with a system to rank tornadoes according to how much damage they cause. He devel-
oped his categories by connecting the twelve forces of the Beaufort wind scale (knots
based on what the sea surface looks like—from smooth to waves over 45 feet) with the
speed of sound (Mach 1). Then, for each category he estimated how strong the wind
must be to cause certain observed damages. Fujita’s scale was later combined with
Pearson’s scale, which measures the length and width of a tornado’s path, or its con-
tact with the ground.

Fujita Tornado Scale

F- Wind
Scale Intensity Strength Frequency Damage Description

F0 Gale 40-72 mph 29% Some branches break off trees; some
tornado (64-116 kph; damage to buildings, such as to roof
35-62 knots) shingles and windows; billboards and other
signs show damage 311

MATH IN THE NATURAL SCIENCES