The southwest monsoon is unlikely to set in over Kerala on Friday as expected, as the criteria set for the declaration of the arrival of monsoon are yet to be fulfilled.
According to the parlance of the India Meteorological Department (IMD), 60% of the listed 14 rainfall monitoring stations in Kerala should report a rainfall of 2.5 mm or more for two consecutive days for the declaration of the arrival of the monsoon. Further, the depth of westerlies should be maintained up to 600 hPa along with persistent convection (cloudiness indicated by Outgoing Longwave Radiation (OLR) values).
All these criteria are not met except outgoing long wave radiation, which is almost reaching but not consistent on all days.
Picking up momentum
“It seems the westerlies are likely to pick up momentum only by May 30 or 31. So the onset of monsoon over Kerala is unlikely before May 30, but it could happen anytime after May 30,” said a senior IMD source.
The rain Kerala has been experiencing for the past few weeks is pre-monsoon rain influenced by the northwesterly winds. Severe thunder at isolated places along with cumulonimbus clouds is normally associated with the northwesterly.
During monsoon the rainfall will be carried by southwesterly, which would replace all cumulonimbus clouds with stratus clouds that will not give severe thunderstorms, said the senior scientist.
K Santhosh, director, IMD Meteorological Centre, Thiruvananthapuram, said the southwest monsoon had advanced into some parts of the southwest Arabian Sea, some more parts of southeast Arabian Sea, the Maldives and Comorin area and the south Bay of Bengal.
Further, the conditions are favourable for the advance of southwest monsoon over some more parts of south Arabian Sea, the entire Maldives and adjoining areas of Lakshadweep and some more parts of the Comorin area during next 48 hours. The IMD is continuously monitoring the progress of monsoon over Kerala, said Mr. Santhosh.
Yellow alert
Meanwhile, the IMD has sounded a yellow alert in nine districts, except Thiruvananthapuram, Kollam, Palakkad, Kannur and Kasaragod, on Friday warning of isolated heavy .
With hardly five days left on the pre-monsoon calendar, the State has so far received 108% excess rainfall of 63.15 cm in the season against the average of 30.38 cm during this period.
The IMD earlier forecast that the southwest monsoon, also known as Edavapathy, is likely to set in over the State by May 27, five days earlier than the normal onset date.
