Thunderstorms

THUNDERSTORMS

Nature's violence unleashed

Thunderstorms

In Malaysia, thunderstorms are a common phenomenon occurring all year round, frequently during the afternoon and early evening. Despite their small size, all thunderstorms are dangerous. Every thunderstorm produces lightning which has the potential to kill people.

Heavy rain from thunderstorms can lead to flash flooding and landslides. Strong winds and hail are also dangers associated with some thunderstorms.
	Flash floods caused by thunderstorms	Landslides caused by thunderstorm rain

What is a thunderstorm ?

Thunderstorm is defined by the World Meteorological Organization as one or more sudden electrical discharges, manifested by a flash of light (lightning) and a sharp or rumbling sound (thunder).

	A thunderstorm usually develops in an unstable and moist atmosphere.
	A cumulus cloud is formed when warm moist air from the surface rises and is lifted to higher altitude and condenses.
	It grows laterally and vertically into a large dense cloud called cumulonimbus, with strong turbulence within the cloud and strong outflow below the base of the cloud.
	The mature thunder cloud often has a cellular structure with diameter that can reach 3 to 5 kilometers and its top exceeding 10 kilometers. Thunderstorm cells may occur singly, in clusters, or in lines.
	Thunderstorms last an average of 15 to 30 minutes but may last much longer in some storms.

Thunderstorms are capable of producing hail, heavy rain, frequent lightning and strong gusty winds. Some of the most severe weather occurs when a cluster of thunderstorms affect an area for a prolonged period of time.

Downburst

Downburst is a term used to describe a small area of rapidly descending air beneath a thunderstorm. The strong winds can reach very high speeds causing significant damage along its path and is extremely dangerous to aviation.

WATERSPOUT

Waterspout with thunderstorm

Other phenomena which can occur during thunderstorm is waterspout. Waterspout is an air vortex which forms over surface of water and frequently occurs in the tropics. Waterspout can cause danger particularly to the boaters. Safety rules that should be taken when facing this situation are :-

Try to escape from its path.
If it's about to hit your boat, dive overboard. Flying debris in the vortex may cause injury.

What is lightning ?

The action of rising and descending air within a thunderstorm cloud separates positive and negative charges. Lightning is the discharge produced when differences between ground and atmospheric electrical charges are large enough to overcome the insulating effect of the air. Lightning can occur within cloud, cloud to cloud, and between cloud and ground. Lightning often strikes outside of heavy rain and may occur as far as 10 miles away from any rainfall.

Air near a lightning strike is heated to above 20,000 ^oC - hotter than the surface of the sun. Rapid heating and cooling of air near the lightning causes a shock wave that results in thunder.

Lightning can damage electrical installations and induce fires. Most lightning deaths and injuries occur when people are caught outdoors.

Most Frequent Period For Thunderstorms

Thunderstorms can occur throughout the year but are most likely to happen in the intermonsoon periods, namely April to May and October to November. Over land, thunderstorms frequently develop in the afternoon and evening hours while over the sea, thunderstorms are more frequent at night.

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