Knowledge about storms
14/09/2014 07:41:21

Da Nang is a coastal city of Vietnam, often suffering from natural disasters, especially storms. According to statistics, during the period from 1998 to 2013, Danang suffered from 26 storms and 14 tropical depressions. Total damage from storms cost the city nearly 7,000 billion dong. This article will share with our readers the basic knowledge of tropical depressions and storms.
 

1. WHAT IS STORM AND TROPICAL DEPRESSION?

Storms and tropical depressions are a tropical cyclone with strongest wind power close to the centre above level 6 (above 39km/h). In weather forecast, it is distinguished that:
- Tropical depressions are when strongest wind power close to the cyclone center is at level 6-7.
- Storms are when strongest wind power close to the cyclone center is above level 8 (above 17.2m/s)
 
2. WHAT THE CONDITIONS FOR FORMATION OF A STORM?
 

Storm is a tropical cyclone structured by humid air mass with very strong sharp lines around the eye, creating swirling cloud and rain in the center of the storm. The energy of the storm is hiding energy of the giant amount of water steam evaporated from the ocean. In addition, the formation of storms requires instable air flow ensuring for the formation of deep convection and thunderstorms.

Hurricanes can only form when there are enough 3 conditions: heat, moisture and momentum to create a vortex.
 
Meteorologist Erik Palmen figured out that storms were only able to form on the sea in 5 – 20o latitude on either side of the Equator with high temperature (above 26 - 27°C) - ensuring sufficient amount of steam evaporated from the sea surface to supply energy for storm formation and coriolis force being strong enough to create whirlpools and favorable conditions for storm formation. Storm cannot form in the 0 - 5o latitude on both sides of the Equator because the coriolis force is too small to create a vortex.

3. HOW IS A STORM FORMED?
 

Initially, the storm is a low-pressure area with swirling air flow into the centre in clockwise direction (in the Northern hemisphere). In favorable conditions, this low-pressure area can become larger; the winds close to the centre become stronger, developing into tropical depression and bigger storms.
 
4. WHAT IS STORM EYE?

 
Storm eye is the area with the lowest barometric pressure in the storm, mostly silent winds, cloudless and higher temperature (due to increasing heat of the air stream). The air diameter is from 30 – 60km.
 


Storm eye of 2013 Haiyan from the satellite

 

5. HOW ARE STORMS IN THE NORTH WEST OF PACIFIC OCEAN CLASSIFIED?
 
Based on the speed of strongest winds close the center of the tropical cyclone, the World Meteorological Organization (WMO) classify tropical cyclones as follows:
 
(1) TD – Tropical depression: Tropical cyclone with strongest wind power level 6 - 7 (10.8 – 17.2m/s).
 
(2) TS – Tropical storm: Tropical cyclone with strongest wind power level 8 - 9 (17.3 – 24.4m/s).
 
(3) STS – Severe Tropical Storm: Tropical cyclone with strongest wind power level 10 – 11 (24.5 – 32.6m/s).
 
(4) Ty: Typhoon: Tropical cyclone with strongest wind power above level 11 (above 32.6m/s).

 
 

 

Route of Haiyan typhoon in 2013 

 

                                                                                                                                                           Mai Huong
 

 
 
 
 
 
 
 
 
 
 
 
 
 
              
 
 
 
 
 
 
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