Degrees of possible disaster
The Saffir-Simpson Hurricane Scale rates
each storm on a scale of 1-to-5. The scale is based primarily
on the strength of the winds. This scale gives an idea of the
damage and flooding islanders can expect when a hurricane hits.
See further below for a description
of each category.
|| Winds* (km per hour)
than 5.50 m
Most weather stations and meteorologists measure wind
speed in "knots". Popular media converts this
to "kilometers per hour", or "miles per
"Hurricane Ismael's winds have been clocked at 200 kph,
making it a Category 3 hurricane. It is going to cross your
This announcement might make a great start
for an exciting computer game or a white-knuckle, action movie.
However, it is a grim reality every year to millions of people
living in the tropics. The devastation is caused in a variety
Winds. A photograph taken after one hurricane
showed a wood plank that was seized by the wind and driven through
a palm tree as if the plank were a well-sharpened knife. Other
photographs showed large sugar mills reduced to rubble; hamlets
of wood and thatch homes erased from the face of the planet;
telephone and electrical cables balled up in masses of tangled
wires; plantations of bananas and lime trees destroyed. The
winds move through with such force that pieces of wood, sections
of zinc roofs, flowerpots, lawn chairs, and tricycles become
Rains. More rain can fall on one mountainside
during a seven-hour hurricane — 635 mm. is not a record-breaking
amount — than falls on Southern California in an average year!
The waters in streams and on coastal flood plains can grow up
to ten times their normal size. As they tumble to the sea, they'll
sweep people, cars, and buildings with them as if they were
mere toys. The rains also trigger massive landslides of super-saturated
soil down the steep slopes, which are common on many of the
volcanically-formed Caribbean islands.
Waves. Mariners once recorded hurricane waves
that dragged a ship with a buoy, chain, and anchor weighing
more than 13,600 kg, for 16km! Imagine what these waves can
do when they hit a low-lying coastal community. Tidal surges
temporarily raise the local sea level and submerge entire coastal
areas. Tidal surges cause the greatest number of hurricane deaths.
While all this is happening, rescuers
can do nothing but sit and wait for the hurricane to pass, for
it is far too dangerous to venture out. When the hurricane does
finally pass, roads are often impassable, lines of communication
destroyed. Rescue efforts are extremely difficult.
A hurricane watch
is issued when there is a threat of hurricane conditions
within 24 or 36 hours.
What should I do?
Everyone in the area covered by the "watch"
should listen to their radios and television for weather
updates and be prepared to act promptly if a hurricane
warning is issued. Prepare to either bring in or place
in a secure location any lawn furniture, outdoor decorations,
trash cans, hanging plants, and anything else that can
be picked up by the wind. You should also cover all
windows of your home. Also, prepare a Disaster Safety
& Supply Kit.
A hurricane warning is issued when hurricane winds reach
74 miles an hour or higher, or a combination of dangerously
high water and rough sea conditions are expected in 24
hours or less.
What should I do?
Everyone in the area covered by the "warning"
should take precautionary actions to prepare for the
full force of the hurricane. You should listen to local
officials and leave if they tell you to do so. If you
are not advised to evacuate, stay indoors and away from
windows. You should also be alert of tornadoes and remain
indoors, in the center of your home, in a closet or
bathroom without windows
Tropical disturbance, tropical wave:
Unorganized mass of thunderstorms, very little, if any, organized
Tropical depression: Evidence of
closed wind circulation around a center with sustained winds
from 37-63 kph.
Tropical storm: Maximum sustained
winds are from 64-118 kph. The storm is named once it reaches
tropical storm strength.
Hurricane: Maximum sustained winds
exceed 119 kph.
Simpson Hurricane Intensity Scale
Category One - A Minimal Hurricane
- Winds: 119-153 kph, 64-83 kts.
- Minimum surface pressure: higher than 980
- Storm surge: 1.22 - 1.81m.
- Damage primarily to shrubbery, trees, foliage,
and unanchored homes. No real damage to other structures.
Some damage to poorly constructed signs. Low-lying coastal
roads inundated, minor pier damage, some small craft in exposed
anchorage torn from moorings. Example: Hurricane Jerry (1989)
Category Two - A Moderate Hurricane
- Winds: 154-177 kph, 84-96 kts.
- Minimum surface pressure: 979-965 mbar.
- Storm surge: 1.82 - 2.72 m.
- Considerable damage to shrubbery and tree
foliage; some trees blown down. Major damage to exposed mobile
homes. Extensive damage to poorly constructed signs. Some
damage to roofing materials of buildings; some window and
door damage. No major damage to buildings. Coast roads and
low-lying escape routes inland cut by rising water 2 to 4
hours before arrival of hurricane center. Considerable damage
to piers. Marinas flooded. Small craft in unprotected anchorages
torn from moorings. Evacuation of some shoreline residences
and low-lying areas required. Example: Hurricane Juan (2003)
Category Three - An Extensive Hurricane
- Winds: 178-209 kph, 97-113 kts.
- Minimum surface pressure: 964-945 mbar.
- Storm surge: 2.74 - 3.99 m.
- Foliage torn from trees; large trees blown
down. Practically all poorly constructed signs blown down.
Some damage to roofing materials of buildings; some wind and
door damage. Some structural damage to small buildings. Mobile
homes destroyed. Serious flooding at coast and many smaller
structures near coast destroyed; larger structures near coast
damaged by battering waves and floating debris. Low-lying
escape routes inland cut by rising water 3 to 5 hours before
hurricane center arrives. Flat terrain 1.5 meter or less above
sea level flooded inland 13 km. or more. Evacuation of lowlying
residences within several blocks of shoreline possibly required.
Example: Hurricane Gloria (1985)
Category Four - An
- Winds 210-249 kph, 114-135 kts.
- Minimum surface pressure: 944-920 mbar
- Storm surge: 4 - 5.50 m.
- Shrubs and trees blown down; all signs
down. Extensive damage to roofing materials, windows and doors.
Complete failures of roofs on many small residences. Complete
destruction of mobile homes. Flat terrain 3 meter or less
above sea level flooded inland as far as 10 km. Major damage
to lower floors of structures near shore due to flooding and
battering by waves and floating debris. Low-lying escape routes
inland cut by rising water 3 to 5 hours before hurricane center
arrives. Major erosion of beaches. Massive evacuation of all
residences within 500 meters of shore possibly required, and
of single story residences within 3.2 km. of shore. Example:
Hurricane Andrew (1992)
Category Five - A Catastrophic Hurricane
- Winds: greater than 250 kph, 135 kts.
- Minimum surface pressure: lower than 920
- Storm surge: higher than 5.5 m
- Shrubs and trees blown down; considerable
damage to roofs of buildings; all signs down. Very severe
and extensive damage to windows and doors. Complete failure
of roofs on many residences and industrial buildings. Extensive
shattering of glass in windows and doors. Some complete building
failures. Small buildings overturned or blown away. Complete
destruction of mobile homes. Major damage to lower floors
of all structures less than 4.6 meters above sea level within
500 meters of shore. Low-lying escape routes inland cut by
rising water 3 to 5 hours before hurricane center arrives.
Massive evacuation of residential areas on low ground within
8 to 16 km. of shore possibly required. Example: Hurricane
- What type of damage would you expect to find in a Category
- Identify three causes of devastation during a hurricane.
- A hurricane hits a nearby island. Damage is found to shrubbery
and trees, but most homes and buildings are not affected.
Minor damage was done to piers and small boats. None of the
roads on the island flooded. The above description is most
likely of a Category _________ hurricane.