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THE STORMS

1st PART
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DESCRIPTION OF A STORM

CONDITONS OF DEVELOPMENT

CONSEQUENCES OF STORMS

STORM OF 1999 IN FRANCE

STORM OF 2010 (Xynthia) IN FRANCE


DESCRIPTION OF A STORM

A storm is a disturbance associated with a center of low atmospheric pressures. The latter causes strong winds that rotate around the center of low pressure in the the opposite of clockwise in the northern hemisphere and reverse in the southern hemisphere. They move at an average speed of 40 km/h to 50.km/h, allowing them to cross France in three days on average. A storm is faster than tropical cyclone that moves with an average speed of 20 km/h.

Depression is highly skewed when a cyclone is symmetric around its eye.

When the Beaufort strength is 10 to 11 (90 to 117 km/h), it is called storm. By international convention, storm warnings are reported from a Beaufort force of 10 to 11 (90 to 117 km/h). With such winds, waves reach impressive heights.

This is from a Beaufort force 12 or winds of over 118 km/h on the average, we're talking about hurricane. The waves can reach 15 meters with a wind of 130.km/h. What is rare on land, but it has happened.

Storms can go with, preceded and followed by heavy rainfall and sometimes thunderstorms.

The storm of 02/03/1994 : METEOSAT 4

LEGENDE
  Sea and areas of clear sky
  Cirrus
  Cumulonimbus
  Cumulus and stratocumulus
  The soil at high temperature

  • SCALE OF BEAUFORT WINDS

Strength of beaufort


generic term

wind speed
at
10 m of height


sea conditions

(degree)

(descriptive)

in km/h

in knot

(remarks)


0


Calm


less than 1


less than 1

Smoke rises vertically ; the sea is calm and looks like a mirror


1


Very light freeze


1-5


1-3

Wrinkles are formed, but there isn't foam


2


Light breeze


6-11


4-6

Short wavelets ; their crests don't break


3


Low breeze


12-19


7-10

Very small waves ; foam of glassy appearance


4


Nice breeze


20-28


11-15

Small waves becoming longer ; many sheep


5


Fine breeze


29-38


16-21

Moderate waves, elongated ; many sheep


6


Fresh wind


39-49


22-26

Blades are formed ; larger white foam crests


7


Great cool


50-61


27-33

Sea swells ; the foam is blown in streaks ; breakers


8


Gale


62-74


34-40

Waves of medium height ; from their ridges remove swirls of spindrift


9


Strong gale


75-87


41-47

Large waves ; their peaks collapse and break in rolls


10


Storm


88-102


48-55

Very heavy waves with long crests in plume ; breaking in intense and brutal roller


11


Violent storm


103-117


56-63

Exceptionally high waves ; covered sea of white bench of foam


12


hurricane


more than 118


more than 64

Outdoor foam and spray ; sea completely white ; very reduced visibility

 


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