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These are a natural threat involving
the air around us. We cannot stop storms from
happening, but we can prepare for them - and survive them.
Damaging wind is caused by deep depressions or tornadoes.
A depression is a low pressure weather system.
Air in this system rotates around the centre and is sucked inwards and upwards.
Depressions are also commonly known as "lows". Deep
depressions can be recognised by the concentric circles drawn on weather maps.
The closer together the lines are drawn, the stronger the wind is.
When strong winds cross a mountain range, they
sometimes become exceptionally strong downwind from the mountains.
Tropical cyclones form in the tropics during summer
and early autumn and can move south towards New Zealand. When this
happens, tropical cyclones sometimes change into deep depressions, bringing
heavy rainfall to some areas and gale force winds to others.
In a tropical cyclone, the strongest winds are near
the centre. In a deep depression that has formed from a tropical
cyclone, the strongest winds are often hundreds of kilometres from the centre.
These depressions usually affect the North Island more than the South Island.
Strong winds which come from "lows" forming in the
Tasman Sea or south of New Zealand, usually affect the South Island and the
lower half of the North Island, especially in late winter or early spring.
Tornadoes
Tornadoes are narrow funnels of violently spinning
air which descend from the bases of cumulo-nimbus cloud. They often
last only for a few minutes and the path of destruction may be only 50 metres
wide.
Tornadoes develop very quickly, often without
warning – except for the presence of giant towering clouds.
Storm surges
Gale or storm winds blowing directly from the sea to
land can sometimes cause the sea to invade the land. The effect is
worse where the sea bed is shallow for a long way offshore and when there is a
spring tide. Low air pressure associated with a deep depression,
will also help to raise the sea level.
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SOME DESTRUCTIVE STORMS IN
NEW ZEALAND’S HISTORY |
| February
1936 |
Cyclonic
storm over much of
the North Island |
| August
1948 |
Tornado at
Hamilton.
3 people killed. |
| November
1967 |
Tornado at
Woodville |
| April 1968 |
Ex
tropical cyclone "Giselle"
(Wahine Storm) |
| August
1975 |
Damaging
winds affect regions from Otago to the Wairarapa |
| March 1976 |
Ex
tropical cyclone "Alison" |
| July 1978
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Severe
wind damage in
the Te Aroha district. |
| March 1988
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Ex
tropical cyclone "Bola" |
| October
1988 |
Damaging
winds affect Canterbury. |
| August
1990 |
Damaging
tornado hits Taranaki
towns of Bell Block and Inglewood. |
Severe wind warnings
A severe
wind warning is issued when winds of more than 70 km/h are expected over land.
The
warning is issued by the National Weather Forecasting Centre in Wellington to
the Police and the Ministry for Emergency Management. The Police
then warn radio stations, and Civil Defence organisations are warned by the
Ministry for Emergency Management.
The
National Weather Forecasting Centre also provides the news media with daily
weather forecasts.
If strong
winds cause danger to the public, a civil defence emergency may be declared.
This occurred in Taranaki in March 1988 during Cyclone "Bola".
Develop a family plan so that each
person knows:
| what to do to survive
a storm |
| what to do if a storm
prevents them from returning home. |
Help your neighbours to develop a plan for
getting help during a storm. Talk to your Civil Defence organisation
about this.
Storm hazards
Severe Winds
- roofing iron may be torn off houses and fly free
- motor vehicles can be blown off the road
- telephone boxes, bus shelters and walls can be
blown over
- trees and branches may snap
- power lines can be blown down
- large panes of glass may break.
Tornadoes
- objects in its path may be shredded
- items torn free may become fast moving missiles
Storm surge
- the sea will be higher than usual and may flood
sections near the beach
Emergency
Preparedness
Right Now:
Check your disaster survival kit at home and at work. Check the civil
defence pamphlet Your
Disaster Survival Kit for items that you
should include in the kit.
Check:
- Batteries in torches and radios in case the
power supply is lost during the storm
- Food and emergency water supplies
- The first aid kit
- Important documents such as insurance papers,
birth certificates and passports
- Essential medicine supplies
- The roof, for loose iron sheets and tiles – fix
these.
- The exterior television aerial – secure it to
the roof.
When a strong
wind warning is received
During the storm
- Stay inside. Don’t walk around outside – you may
be hit by flying debris.
- Don’t go driving unless absolutely necessary.
- Listen to the nearest operating radio station
for information. Be sure to use a battery powered radio since power may be cut.
- Close the curtains – this will slow down flying
glass or other loose objects.
- Stay away from doors and windows. If the wind
becomes destructive, shelter further inside the house. If you can
move a mattress, use this for added protection.
- During an electrical storm, stay away from metal
and electrical fixtures in your house. These can act as lightning conductors.
- If your house or building is severely damaged by
the wind, contact your local council.
- Open a window on the side of the building away
from the wind – this will help relieve pressure on the roof.
- Be prepared to take essential items with you if
emergency services ask you to evacuate.
After the storm
Avoid
dangling and broken power lines. Report these to the nearest electrical
authority.
Contact your local council for advice in cleaning up debris from wind damage.
REMEMBER ...
You will need to know in advance how to contact your
local civil defence organisation for assistance during an emergency. Contact
your organisation through your local council and find out what they would prefer
you to do.
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