FPJ Explains: Cyclone Tauktae - What does very severe cyclonic storm mean? How are cyclones classified?

Cyclone Tauktae has intensified into a very severe cyclonic storm and will cross the Gujarat coast in the morning of May 18, as per the Indian Meteorological Department on Sunday.

What is a cyclone?

A "Cyclonic Storm" or a "Cyclone" is an intense vortex or a whirl in the atmosphere with very strong winds circulating around it in an anti-clockwise direction in the Northern Hemisphere and in a clockwise direction in the Southern Hemisphere.

The word "Cyclone" is derived from the Greek, word "Cyclos" meaning the coils of a snake. To Henri Peddington, the tropical storms in the Bay of Bengal and in the Arabian Sea appeared like the coiled serpents of the sea and he named these storms as "Cyclones".

Cyclones are intense low-pressure areas - from the centre of which pressure increases outwards- The amount of the pressure drop in the centre and the rate at which it increases outwards gives the intensity of the cyclones and the strength of winds.

What does very severe cyclonic storm mean?

Cyclone with windspeed 64 to 119 knots ( 119 to 221 kmph).

How are cyclones classified?

The criteria followed by the Meteorological Department of India to classify the low-pressure systems in the Bay of Bengal and in the Arabian Sea as adopted by the World Meteorological Organisation (W.M.O.) are:

Types of Disturbances

Associated wind speed in the Circulation

1. Low Pressure Area

Less than 17 knots ( < 31 kmph)

2. Depression

17 to 27 knots ( 31 to 49 kmph)

3. Deep Depression

28 to 33 knots ( 50 to 61 kmph)

4. Cyclonic Storm

34 to 47 knots ( 62 to 88 kmph)

5. Severe Cyclonic Storm

48 to 63 knots ( 89 to 118 kmph)

6. Very Severe Cyclonic Storm

64 to 119 knots ( 119 to 221 kmph)

7. Super Cyclonic Storm

120 knots and above ( 222 kmph and above)