The India Meteorological Department (IMD) has forecast that the northeast monsoon over the southern peninsular region, including Tamil Nadu, will be normal to above-normal this year.
The seasonal rainfall between October and December over the southern peninsular region is likely to be normal, logging 88% to 112% of the long period average, which is 33.4 cm. Officials of the Regional Meteorological Centre, Chennai, noted that the IMD’s seasonal outlook is usually provided for the entire region. While conditions are becoming favourable for complete withdrawal of the southwest monsoon by October 15, weather would be monitored for the onset of the northeast monsoon from around that time (the normal onset of the northeast monsoon happens around October 20), they said.
The combination of global weather phenomena, El Nino and Indian Ocean Dipole (IOD), involving sea surface temperature variability in the Indian and the Pacific Oceans and their influence on rainfall over the Indian region would continue to prevail, the officials added.
S. Balachandran, Additional Director General of Meteorology, Chennai, said that going by the records since 1901 in Tamil Nadu, rainfall during the northeast monsoon had either been normal or in surplus during 16 occasions when a combination of El Nino and IOD had prevailed.
“Tamil Nadu may experience normal to above normal rain this year going by the past records. We have received normal rain during the northeast monsoon in eight such years and excess rain during six years. The State experienced a rain deficit only during two years,” he said.
Tamil Nadu’s average rainfall during the northeast monsoon is 44 cm. Multiple factors, including transient systems like easterly waves and Madden-Julian Oscillation (MJO) influence it. Weather systems like cyclones move west-northwestwards and have a short track during El Nino years, he added.
This year, Tamil Nadu has had normal southwest monsoon as IMD considers September as the month that it officially ends. Wet cover that persisted for many days in September had helped the State scrape through with 8% more rain than average this year.
Mr. Balachandran noted that this southwest monsoon ended in complete contrast to last year. The State had received 45% surplus rain during the previous monsoon. While there was good rain between June and August last year, this year, most of the rainfall occurred in September.
Similarly, Chennai was among the districts that received surplus rain this season. It received 74% in excess of its average of 44.8 cm. Last year, it received only normal rain during the southwest monsoon. A good MJO and development of convective activity in September had led to good monsoon. Meenambakkam received 94.6 cm of rain for the season, one of the highest amount received in the past few decades. The department has forecast wet weather to continue over the State till October 6.
