This year could see frequent and more intense cyclones over the Bay of Bengal during October-November and a relatively higher frequency of cold waves during winter season, India Meteorological Department chief M Mohapatra has said.
“We associate La Nina years with a higher frequency of intense cyclones over Bay of Bengal and colder winters. But many other factors influence the winter. A forecast will be issued in November for the winter months. But if we consider only the impact of La Nina then that is definitely linked to colder winters,” Mohapatra said in response to a query during a webinar organised by National Disaster Management Authority.
La Nina conditions have already set in, he said.
IMD in its El Niño Southern Oscillation (ENSO) bulletin for October said currently, weak La Niña conditions are prevailing over equatorial Pacific and sea surface temperatures (SSTs) are below normal over central and eastern equatorial Pacific.
El Niño and the Southern Oscillation (ENSO) is a periodic fluctuation in sea surface temperature and the air pressure of the overlying atmosphere across the equatorial Pacific Ocean according to the National Oceanic and Atmospheric Administration (NOAA).
ENSO has a major influence on weather and climate patterns such as heavy rains, floods and drought.
El Niño has a warming influence on global temperatures, whilst La Niña has the opposite effect.
In India for example, El Nino is associated with drought or weak monsoon while La Nina is associated with strong monsoon and above average rains and colder winters.
The latest forecast indicates cooling of SSTs will most likely continue and weak La Niña conditions are likely to turn into moderate La Niña conditions during coming months and sustain till early part of the next year. No cyclone has developed this October yet. But the depression over north interior Karnataka and adjoining areas of Maharashtra that moved west-northwestwards has weakened into a well-marked low-pressure area over south Maharashtra. It is likely to move further west-northwestwards and emerge into eastcentral Arabian Sea off the Maharashtra coast by October 16.
It is then very likely to intensify into a depression again during subsequent 24 hours over eastcentral and adjoining northeast Arabian Sea off Maharashtra – south Gujarat coasts, move gradually west-northwestwards and intensify further.
Monsoon withdrawal from northwest India will resume only after these weather systems subside and rain stops.
“Due to La Nina the atmospheric circulation patterns change. There are more western disturbances which bring snow and rain to northern India and cold air from the north infiltrates other parts of northwest India also. This is why La Nina is associated with cold winters. Similarly, the frequency of cyclone formation increases but slightly to the north from its normal position. So you may see more cyclones forming near Odisha, West Bengal, Bangladesh and they have a higher chance of recurving as opposed to cyclones forming near Tamil Nadu or south Andhra Pradesh coasts during non-La Nina years. We are expecting moderate La Nina till the end of the year,” said DS Pai, climate expert and scientist at IMD Pune.