Hurricane Florence: What Category 4 Saffir-Simpson label means

A
hurricane as seen from space.

Flickr/NASA’s
Marshall Space Flight Center

• Hurricane
  Florence is headed for the East Coast of the US as a
  
  Category 4 storm.
• Hurricane intensity is most
  commonly measured by what’s called the Saffir-Simpson scale.
• The scale helps estimate potential property damage and coastal
  flooding caused by storm surge.
• However, the scale is determined by maximum sustained wind
  speeds of a storm.

Hurricane
Florence is headed for the East Coast of the US as a
Category 4 storm.

Hurricanes are storms that are so large they can easily be

seen by astronauts in space, yet they are
tricky-to-categorize weather events.

Over the decades, one classification system has risen above the
rest: The Saffir-Simpson scale.

The Saffir-Simpson scale tries to assess a hurricane’s intensity
and is used to estimate potential
property damage and coastal flooding caused by storm surge —
an abnormal rise of water above the normal tide, generated by a
storm pushing water ashore.

Winds are the primary driver of
storm surge, however, so the scale is determined by wind
speed.

Flooding from storm surge depends on many factors, such as the
storm’s track, intensity, diameter, forward speed of the storm,
and the characteristics of the coastline where it comes ashore or
passes nearby.

Category 1

Winds of 74-95 mph (120-150 kph). Storm surge of 4 to 5 feet (1
to 1.5 meters) above normal. Damage primarily to un-anchored
mobile homes, shrubbery and trees. Some damage to poorly
constructed signs and piers. Extensive damage to power lines and
poles likely will result in power outages that could last a few
to several days.

Category 2

Winds of 96-110 mph (155-175 kph). Storm surge 6 to 8 feet
(1.8-2.4 meters) above normal. Some roof, door and window damage
to buildings. Considerable damage to mobile homes, small
watercraft, trees, poorly constructed signs and piers. Flooding
of coastal and low-lying areas. Many shallowly rooted trees will
be snapped or uprooted and block numerous roads. Near-total power
loss is expected with outages that could last from several days
to weeks.

Category 3

Winds of 111-129 mph (180-210 kph). Storm surge 9 to 12 feet (3
to 4 meters) above normal. Some structural damage to small homes.
Mobile homes destroyed and large trees blown down. Coastal
flooding destroys smaller structures and floating debris damages
larger structures. Terrain lower than 5 feet (1.5 meters) above
sea level may flood as far as 8 miles (13 kilometers) inland.
Hurricane Katrina, the costliest natural disaster in U.S.
history, was a Category 3 storm at landfall in 2005 after being a
Category 5 in the Gulf of Mexico. At least 1,800 people died.

Category 4

Winds of 130-156 mph (210-250 kph). Storm surge 13 to 18 feet
(4-5 meters) above normal. Wall failures and roof collapses on
small homes, and extensive damage to doors and windows. Complete
destruction of some homes, especially mobile homes. Power outages
will last for weeks to possibly months. Major coastal flooding
damage. Most of the area will be uninhabitable for weeks or
months. Two 2004 storms were Category 4: Hurricane Ivan, which
made landfall near Gulf Shores, Alabama, and Hurricane Charley,
which hit the Florida Gulf Coast near Fort Myers. Charley killed
at least 21 people and left thousands homeless. The total U.S.
damage was estimated to be near $15 billion.

Category 5

Winds greater than 157 mph (250 kph). Storm surge greater than 18
feet (5 meters) above normal. Complete roof failure on many homes
and industrial buildings. Smaller buildings and mobile homes
blown over or completely blown away. Major damage to lower floors
of all structures located less than 15 feet (4.5 meters) above
sea level and within 500 yards (460 meters) of the shoreline.
Massive evacuation of residential areas on low ground within 5 to
10 miles (8 to 16 kilometers) inland may be required. The last
Category 5 storm to hit the United States was Hurricane Andrew in
1992. An estimated 250,000 were left homeless and the storm
caused more than $20 billion in damage in the Bahamas, Florida
and Louisiana. Fifty-five people were killed.

Below is a graphic that shows all five categories and what they
mean.

Ana Pelisson/Business Insider

This story has been updated. It was originally published on
September 5, 2017.