Cyclone Phethai heading northward from the Bay of Bengal makes landfall in Andhra Pradesh
- Cyclonic storm Phethai has made a landfall at Katrenikona in Andhra Pradesh’s East Godavari district.
- This is the third cyclone to hit the state this year after Cyclone Daye and Cyclone Titli
- Phethai is relatively less severe when compared to Titli that ravaged Srikakulam district in north coastal Andhra region
What is a cyclone?
- A “Cyclone” is an intense vortex or a whirl in the atmosphere with very strong winds circulating around it in anti-clockwise direction in the Northern Hemisphere and in clockwise direction in the Southern Hemisphere.
- It is a system of low pressure occurring in tropical latitudes
- The differential heating over land and sea probably causes a small area of low atmospheric pressure to develop.
- Tropical cyclone activity is at its maximum in late summer and early autumn
- Tropical cyclones follow a parabolic path; their axis being parallel to the isobars.
- 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.
- Cyclones are of two types: Temperate cyclone and Tropical cyclone. Tropical Cyclones are among the most destructive phenomena.
Necessary Conditions for development of a tropical cyclone and Formation:
- Continuous supply of abundant warm and moist air
- Sea temperature in lower latitudes should be around 27°C
- A distance from the Equator is necessary, so that it allows the Coriolis effect to deflect winds blowing toward the low pressure centre. They develop in inter-tropical convergence zone
- Pre-existence of weak tropical disturbances
- Presence of anticyclonic circulation at the height of 9 to 15km above the surface
- Low vertical wind shear between the surface and the upper troposphere. Vertical wind shear is the magnitude of wind change with height.