The Southwest Monsoon is likely to advance into South Andaman Sea and adjoining Southeast Bay of Bengal around May 15, almost four days earlier than its normal expected date, the India Meteorological Department (IMD) announced on Thursday. Kerala, too, may witness monsoon arrival four days early on May 26, as indicated by the IMD's extended range forecast. However, the official announcement regarding the exact date would be made around May 15 when the IMD issues its second stage South-West Monsoon forecast.
"Fairly widespread to widespread light/moderate rainfall is very likely over Andaman and Nicobar Islands during the next five days. Isolated heavy rainfall is very likely over the region between May 14-16 even as squally weather with wind speed reaching 40-50 kmph, gusting to 60 kmph, is also likely over south Andaman Sea on May 15 & 16," the IMD statement said.
Southwest Monsoon has a wide ranging impact on India's economy with agriculture, economy, trade, travel, almost everything decided by the rainfall quantum and timing. Former Secretary, Earth Sciences, M Rajeevan Nair, said: "Generally SouthWest Monsoon reaches Andaman & Nicobar Islands by May 19-20. This time it is at least a week in advance."
He said, there is no direct correlation between the arrival of SW monsoon at Andaman and Nicobar Islands and that at Kerala. "However, the extended range forecast of IMD shows that conditions will turn favourable, and Kerala will most likely receive southwest monsoon rainfall by May 26."
The heavy rainfall that Kerala has been witnessing for at least the last two days is a side impact of the Cyclone Asani and its remnant system on the east coast, but things would change in the next two days.
At present, the IMD uses a criterion adopted in 2016 for declaring the onset of monsoon over Kerala, which was based on the daily rainfall of 14 stations over Kerala and neighbouring area along with wind field and outgoing longwave radiation (OLR) over southeast Arabian Sea. It emphasises on the sharp increase in rainfall over Kerala along with setting up of large-scale monsoon flow and extension of westerlies up to certain criterion.