What does an early onset of monsoon signify?

The southwest monsoon is likely to set over Kerala by May 27, three days ahead the normal schedule, the India Meteorological Department (IMD) said. 

 “This year, the onset of southwest monsoon over Kerala is likely to be earlier than the normal date of onset. The monsoon onset over Kerala is likely to be on May 27 with a model error of four days,” IMD said.  

Also Read: Depression over Andaman Sea likely to help timely onset of monsoon, says IMD

The onset of monsoon marks the beginning of the four-month period between June and September and brings more than 70 per cent of the country’s annual rainfall. It marks a significant day in India’s economic calendar.  

The IMD announces the onset of the monsoon if at least 60% of 14 designated meteorological stations in Kerala and Lakshadweep record at least 2.5 mm of rain for two consecutive days at any time after May 10. In such a situation, the onset over Kerala is declared on the second day, provided specific wind and temperature criteria are also fulfilled, reported The Indian Express. 

The depth of westerlies should be upto 600 hectopascal (1 hPa is equal to 1 millibar of pressure) in the area bound by the equator to 10ºN latitude, and from longitude 55ºE to 80ºE. The zonal wind speed over the area bound by 5-10ºN latitude and 70-80ºE longitude should be of the order of 15-20 knots (28-37 kph) at 925 hPa.

According to IMD, the INSAT-derived Outgoing Longwave Radiation (OLR) value (a measure of the energy emitted to space by the Earth’s surface, oceans, and atmosphere) should be below 200 watt per sq m (wm2) in the box confined by 5-10ºN latitude and 70-75ºE latitude.

Meanwhile, timely monsoon rains are linked to India’s farm output and economic growth at a time when the country is battling soaring food prices. The war in Ukraine has further pushed up world food costs to a record. India’s farm sector is the main source of livelihood for about 60% of its population and accounts for 18% of the economy.