This week started with an unstable weather here and in the region. We had a thunderstorm on Monday night which continued until the early hours of Tuesday. On Wednesday Mauritiuswitnessed a thundery weather; offices and schools were dismissed earlier. The electricity went off for some time.
On Thursday the weather was cloudy but no thunderstorm as forecast over Rodrigues. Still there was some panic. The school authorities were concerned about the safety pf school children.
The tragic consequences of the torrential rain episode of 26 March in Mauritius are still vivid in their minds. And they know that regions like Riviere Cocos, Port Sud Est, Batatran in the east are particularly prone to flooding during heavy rainfall.
Precautions are even more important during thundery weather. Why? What special precautions are required? In order to answer these questions we need to understand the nature of a thunderstorm.
So let’s see what a thunderstorm is, how it is formed, how it strikes and how you can protect yourself.
A thunderstorm is a storm with lightning and thunder, heavy rain, gusty winds and sometimes hail. It occurs when the atmosphere is unstable. The air is warm and humid. Coupled with active cold fronts and sea breezes it rises to form cumulonimbus clouds with high vertical extent. These clouds, which may reach up to 12 km high, become highly electrically charged and are sometimes referred to as thunder clouds.
The rising air causes the charges to separate; the positive charges concentrate at the top and the negative charges at the base of the clouds. When these charges come into contact, as they certainly will with instability, they produce electrical discharges and huge sparks or thunderbolts. Lightning is visible and seconds after you can hear a rumbling sound, thunder. You see the lightning first because light travels faster than sound. The air temperature at the discharge point may reach about 27 000 oC.
Lightning and Thunder
Lightning is an electric current, a bright flash of electricity produced by a thunderstorm. It is very dangerous and is known to kill more people than tornadoes.
Thunder is caused by lightning which expands the air while finding a path to the ground. When the light is gone the air collapses back creating a sound wave we hear as thunder.
Thunder occurs in our region usually during the period December through April, about three times in a month and 17 days per year. On rare occasions, like this week, thunderstorm occurs in May also. The winter season doesn’t favour the formation of thunder clouds.
Can you assess the distance of a thunderstorm?
Sometimes there’s only lightning, no thunder. Why? Well, the answer is simple. The thunderstorm is far from the point where you are, too far to be heard by the human ear. Usually beyond 10 km you cannot hear thunder.
But if you hear thunder and you want to calculate its approximate distance (in km) just divide by three the time (in sec) elapsed between the moment you see lightning and the moment you hear thunder. (To find distance in miles, divide time by 5).
And if you hear a deafening cracking sound almost momentarily after a lightning then it is most likely that the storm is overhead or very close to where you are. You need to be very vigilant.
Lightning takes the shortest path to the ground. Thus an object that is closer to the cumulonimbus cloud will be the prime target. Trees, mountain tops, high buildings, TV antennas, electric poles, masts, boats in the open sea and the highest point in a plain are all lightning targets. So the basic thing you can do is: stay away from these targets during a thunderstorm.
A lightning strike actually kills and may cause damage to buildings and structures and may even trigger a fire. You’ll protect yourself if you follow simple rules as outlined hereunder:
- Be on the lookout for darkening skies, lightning and increasing winds. These are precursors of a thunderstorm. Pay heed to the weather forecasts. Don’t wait for the rain to begin.
- If you hear thunder, go to a safe place immediately
- If you are at sea, rush to the shore and find a shelter immediately
- If you are in an open area, crouch down; but don’t lay flat, minimize contact with the ground
- If you cannot find a shelter stay away from any tree, at least twice as far away from it as it is tall
- If you are in a forest, seek shelter in a low area under small trees
- If you are on a mountain, climb down immediately
- If you are in a vehicle, stay inside. Don’t touch any metallic parts
- Do not take shower, wash hands, dishes or do laundry. Stay out of water as it is a good conductor of electricity.
- Disconnect all electrical appliances at home or in the office
- Don’t use the corded telephone. Mobile phone is safer.
- Stay off porches and away from doors and windows
- Protect your house or building by installing a lightning conductor or rod. It is a device that provides an easier path for current to flow to the earth than through your house or building. It is made of a vertical metal strip or rod, usually of copper or similar conductive material placed on the roof top and connected to the ground. This system was invented by Benjamin Franklin.
You can assume that the thunderstorm has ceased or moved away if you don’t observe lightning or thunder for at least 30 minutes. You can now resume your routine.