The northeast monsoon is expected to set in over Tamil Nadu on October 26.
Northeasterly winds are likely to set in at the lower tropospheric levels over the Bay of Bengal that day, leading to the parallel retreat of the southwest monsoon and start of the northeast monsoon in the sout- hern peninsular region.
“Normally, the northeast monsoon sets in around October 20. The prolonged southwest monsoon has led to the delay in onset this year...,” The IMD is monitoring the changes in the weather pattern,” said S. Balachandran, Deputy Director-General of Meteorology, Chennai.
The IMD has also forecast a fairly widespread rainfall over the State till October 24. A cyclonic circulation that lies over south Tamil Nadu and a trough extending from the weather system to the northern parts would trigger isolated intense rainfall, particularly over districts in the south and those along the Western Ghats, on Thursday, he said.
Nearly 22 districts, including Tiruchi, the Nilgiris, Namakkal, Salem, Kallakurichi and Vellore, are likely to experience heavy to very heavy rainfall at one or two places. The coastal region is likely to receive light to moderate rainfall on Thursday. Many places in the State and Puducherry would continue to receive rainfall of different intensity till the weekend.
Chennai humid
In Chennai, officials said the increase in moisture in wind during the transition period led to such a humid weather. Thunderstorm with light rain is expected in some areas till Friday, and the maximum temperature may remain around 35 degrees Celsius, three degrees above normal, as it was on Wednesday.
Weather experts noted that many parts of Tamil Nadu had already received a significant share of their annual rainfall. They predicted a good northeast monsoon. Senior meteorologist Y.E.A. Raj said a majority of the places had already received 70%-80% of the annual rainfall. Chennai had so far registered 90 cm against its annual average of 140 cm.
A positive southern oscillation and the chances of La Nina — the global weather parameters that have a strong influence on monsoon — indicate subdued northeast monsoon rainfall. But the northeast monsoon could not be easily judged, given its volatile behaviour, he said.
“We have not had excess monsoon rainfall after 2015. After 2017, the monsoon performance has been only close to normal. We will have to wait for the monsoon this year to break the pattern,” he added.
