New Delhi, May 13 -- The southwest monsoon is likely to make its onset over parts of the Andaman & Nicobar Islands, Andaman Sea and southern Bay of Bengal by the end of the week, days ahead of schedule, the India Meteorological Department (IMD) said on Tuesday. Monsoon usually arrives over the Andaman & Nicobar Islands and their surrounding waters by May 21. The weather system's arrival will set in motion a weeks-long process when rain-bearing clouds begin to spread all over India. "The low-pressure area over Southwest Bay of Bengal lay over the same region at 8.30am on May 12, with the associated cyclonic circulation extending up to 4.5km above mean sea level. It is likely to become more marked during the next 48 hours," IMD said in a statement. The agency said it expects to issue a forecast on the system's arrival over mainland India around May 15, said IMD director general M Mohapatra. Monsoon usually makes its onset over Kerala, the first state it hits on the mainland, on June 1. It then surges northwards in stages and covers all of the country by July 15. Last year, the monsoon made its onset over the Andaman region on May 13. The monsoon is the lifeblood of India's economy. Nearly half of the country's net-sown area lacks irrigation access, making the rain-bearing system vital. It also replenishes 91 natural reservoirs that feed power generation, factories and drinking supply. The rainy season will be especially crucial in the face of geopolitical and weather challenges. It will come as India's cultivators stare at a potential crimp in fertiliser supplies due to the war in West Asia. Scientists have also predicted that an El Nino event, a weather pattern that disrupts the monsoon, may choke the rains. In India, an El Nino - triggered by a warming of the eastern equatorial Pacific Ocean - is associated with a harsher summer and weaker monsoon. Monsoon rainfall over the country this year is likely to be below normal at about 92% of long period average (LPA) - the average rain a region gets over a long stretch - with an error margin of +/-5%, IMD said in its April forecast. India's LPA for the 1971-2020 period is 870mm. HT reported on May 10 that ocean temperatures this April were the highest since a record spell of warmth in 2024, as the world's waters heat up rapidly with a strong El Nino event approaching. IMD also forecast that heatwaves would grip parts of the country over the next few days. Isolated heatwave conditions are likely over Rajasthan, adjoining parts of central India, Gujarat, and Maharashtra. Down south, Tamil Nadu, Puducherry, Karaikal, Kerala, Mahe and southern parts of interior Karnataka are likely to get spells of heavy rain over the next four or five days, the agency added....