Skymet had predicted that monsoon will hit Kerala on May 28 with an error margin of plus or minus 2 days. Whereas, the India Meteorological Department (IMD) had said the monsoon will make an onset over Kerala on June 5, four days after its normal onset date.
Earlier this week, it said a cyclonic circulation in the Bay of Bengal will help in the advancement of the monsoon and it could reach Kerala on June 1, its normal onset date.
According to the IMD, there are three major conditions to declare the onset of monsoon. The first is if, after May 10, 60 per cent of the 14 weather stations -- Minicoy, Amini, Thiruvananthapuram, Punalur, Kollam, Allapuzha, Kottayam, Kochi, Thrissur, Kozhikode, Thalassery, Kannur, Kudulu and Mangalore -- report rainfall of 2.5 millimeters or more for two consecutive days, the onset over Kerala will be declared on the second day. The second is the depth of westerlies should be maintained up to 600 hectopascals (hPa) and the third is the Outwave Longwave Radiation should be below 200 watts per square meter (wm-2).