IMD Director General M Mohapatra said there is cyclonic circulation along the Karnataka coast which is hindering the progress of the Southwest Monsoon.
The arrival of the southwest monsoon over Kerala is likely to be delayed by two days and it is now expected to make an onset over the state by June 3, the India Meteorological Department (IMD) said on Sunday.
However, Skymet Weather, a private forecasting agency, said monsoon has already made an onset over Kerala.
G P Sharma, President (Meteorology) of Skymet Weather, said it is a “very weak onset” this year.
Skymet Weather had earlier predicted that monsoon will make an onset over Kerala on May 30.
IMD Director General M Mohapatra said there is cyclonic circulation along the Karnataka coast which is hindering the progress of the southwest monsoon.
“The southwesterly winds could strengthen further gradually from June 1, resulting in likely enhancement in rainfall activity over Kerala. Hence, the monsoon onset over Kerala is likely to take place around June 3,” the IMD said.
Due to strengthening of lower level southwesterly winds, fairly widespread rainfall activity with isolated heavy falls are very likely over northeastern states during the next five days.
The normal onset date for the monsoon over Kerala is June 1. This marks the start of the four-month rainfall season for the country.
Earlier this month, the IMD had predicted the arrival of monsoon over Kerala by May 31 with an error margin of plus or minus four days.
On Sunday morning, the IMD, in its daily bulletin, said the onset of the monsoon over Kerala was expected to be around May 31. However, by afternoon it said the onset is expected to be by June 3.
“We could have told (the delayed onset) in the morning itself. However, we are monitoring all the defined parameters/criteria for onset of monsoon over Kerala. At present, the criteria is not fully satisfied,” Mohapatra said.
According to the IMD, the onset of the southwest monsoon over Kerala depends on three parameters.
If after May 10, 60 per cent of the 14 stations — 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 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 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.
Sharma said all the IMD parameters are fulfilled to declare the onset of the southwest monsoon over Kerala.
“In the absence of any major monsoon trigger, the onset may be slightly mild. Conditions are favourable for its further advancement to more parts of the south peninsula and east-central Bay of Bengal.Timely progress is expected over northeast India,” Sharma said.
Mohapatra said the rainfall over Kerala decreased on Sunday along with weakening of westerly winds. Also, the depth of westerly winds did not increase up to 4.5 km against the expectation.
The convective cloud development leading to enhancement of rainfall activity over Kerala in such a scenario is not expected at least up to June 1. From June 1, condition will gradually become favourable. “It may lead to onset over Kerala around 3rd June,” he said.
Monsoon is expected to be normal this year, the IMD has said in its forecast.