CHENNAI: If the depression over the southwest Bay of Bengal, which has been bringing rainfall over many coastal regions of TN including Chennai for the last few days, crosses the Sri Lanka coast, it would become the first weather system in 51 years to have formed in January and crossed a landmass.
As of Wednesday evening, IMD said the system was slow moving and may cross Sri Lanka coast by night. The weather agency said the system may continue to bring light to moderate spells over the city and the suburbs and heavy rain over south Tamil Nadu and delta districts on Thursday.
Former IMD official Y E A Raj said since 1971, only nine systems formed over the Bay of Bengal but none made it to the land as they all weakened over the sea due to lack of conducive atmospheric and ocean conditions.
Nevertheless, weather systems could still form and intensify over the Bay if the equatorial trough or the inter tropical convergence zone (ITCZ), which is a band of low pressure with clouds and showers near the equator, moves a few degrees north of the equator. The band of clouds in ITCZ is because of the convergence of northeast winds over Bay of Bengal and northerly or westerly winds closer to the equator. ITCZ normally stays close to the equator in the month of January.
“Weather systems forming in January are reasonably rare. Since 1971, only nine depressions have formed during January-February months, most of them over central Bay of Bengal. They all dissipated over the sea and did not cross the Tamil Nadu coast. Except for two systems which came close to Sri Lanka, no systems crossed Sri Lanka as well,” he said.
Blogger Pradeep John had tweeted that Madden-Julian Oscillation (MJO) phenomenon, an eastward moving pulse of clouds and rainfall which is now lying over the Indian ocean region, could be supporting the system.
N Senthamarai Kannan, director, regional weather forecasting centre, IMD Chennai said the depression remained stationary for more than six hours and started moving slowly. “Systems that form close to the equator normally move slowly,” he said.
For the next 48 hours, the city and the suburbs, which have been receiving patchy rainfall since Monday, are likely to get light to moderate rainfall in some areas. Temperatures may be around a maximum of 30°C-31°C and a minimum of 23°C.