our correspondent
New Delhi/ Thiruvananthapuram: The IMD announced the onset of Southwest Monsoon over Kerala on Thursday, marking the commencement of the four-month rainy season in the country.
Rains lashed most places in Lakshadweep and parts of Kerala, according to a weather bulletin in Thiruvananthapuram.
"The Southwest Monsoon has made an onset over southern parts of Kerala, IMD Director General Mrutunjay Mohapatra said.
According to the India Meteorological Department (IMD), the rains arrived two days later than its normal schedule of June 1. This is the third time in the last six years that monsoon arrived late. In 2016 and 2019, Southwest Monsoon made an onset over Kerala on June 8.
A good monsoon is critical to the Indian economy which is still largely based on agriculture and its allied activities.
Most parts of the country are expected to receive normal to above normal rainfall during the season, the IMD said.
As rains lashed parts of Kerala, the IMD sounded a 'yellow alert' for eight districts -- Pathanamthitta, Alappuzha, Kottayam, Ernakulam, Idukki, Kozhikode, Kannur and Kasaragod -- indicating the possibility of isolated heavy rainfall. Southwest Monsoon is likely to advance into remaining parts of south Arabian Sea and some parts of central Arabian Sea, remaining parts of Kerala, Lakshadweep, some parts of Tamil Nadu, Puducherry, coastal and south interior Karnataka, Rayalaseema, and south and central Bay of Bengal during the next two days, the IMD said.
The IMD had earlier forecast that monsoon would make an onset over Kerala around May 31. Skymet, a private weather forecasting station, said Southwest Monsoon made an onset over Kerala on May 30. However, the IMD said conditions were not ripe for declaring the onset of monsoon.
According to the IMD, three parameters need to fulfilled for declaring the onset of the Southwest Monsoon over Kerala -- If after May 10, 60 per cent of the 14 stations including Minicoy, Amini, Thiruvananthapuram, Punalur, Kollam, Allapuzha, Kottayam, Kochi, Thrissur, Kozhikode, Thalassery, Kannur, Kudulu and Mangalore report rainfall of 2.5 millimetres or more for two consecutive days, the onset over Kerala can be declared on the second day, provided other two criteria are also in concurrence.
This has to be supplemented by the wind speed. The depth of westerlies should be maintained up to 600 hectopascal (hPa), in the box equator to Latitude 10-degrees north and Longitude 55 degrees to 80-degrees east.
The zonal wind speed over the area bounded by Latitude 5 to 10-degrees north, Longitude 70-80-degrees east should be of the order of 15-20 knots at 925 hPa, the IMD said.
The Outgoing Longwave Radiation (OLR) should be below 200 watt per square meter (wm-2) in the box confined by Latitude 5-10 degrees north and Longitude 70-75 degrees east, it added.
The IMD said these parameters were fulfilled on Thursday, it said. Last year, the IMD revised its onset date over several parts of the country. According to the revised onset dates, the normal date for the monsoon to reach Mumbai is June 11, Delhi (June 27),
Chandigarh (June 28), Barmer (July 5). The normal date for the monsoon to reach Bikaner and Pokhran is July 6 and by then it covers the entire country.