India Meteorological Department (IMD) on Sunday declared monsoon onset over the Kerala coast, which arrived three days ahead of normal on June 1. After it failed to arrive on Friday (May 27) as predicted earlier, the weather bureau on Saturday had said monsoon onset might take another 2-3 days.
“All the conditions for the onset of monsoon over Kerala have been satisfied today (May 29, 2022),” IMD said in a statement confirming the arrival.
Conditions satisfied for declaration of onset include depth of westerly winds extending up to 4.5km above sea level, the strength of the westerly winds has increased over the south-east Arabian Sea in lower levels and is about 25-35kmph.
Besides, cloudiness over the south-east Arabian Sea and adjoining areas of Kerala have increased and the average outgoing longwave radiation (OLR) of 189.7 W/M2 (thus <200 W/M2) over the region is met.
“There has been widespread rainfall activity over Kerala during past 24-hours and out of 14 rainfall monitoring stations for declaring the onset of monsoon over Kerala, 10 stations have received rainfall of 2.5mm or more,” IMD said.
The monsoon map shows its arrival in parts of north Kerala much earlier than normal (June 2-5) while some parts of Tamil Nadu like Nagapattinam have not received it which normally they experience on the first onset day.
Madden-Julian Oscillation
Some global models had suspected that monsoon this year might take much longer to precipitate classical onset conditions because, for one, it did not have a friendly Madden-Julian Oscillation (MJO) wave to hitch a ride on. For another, it had to contend with a negative Indian Ocean Dipole (IOD) nibbling away at the monsoon flows midway.
Private weather forecaster Skymet has said the diverse stand of La Nina over Pacific and IOD is raising the complexity of Monsoon 2022. “La Nina remains powerful of the two, but negative IOD events will be under the scanner for any adverse effects.”
The latest IOD index value for the week ending May 22 was -0.55°C, below the threshold of -0.4°C. There is a general consensus amongst numerical models for negative IOD events to develop in the coming months, Skymet said.
‘Low accuracy’
“Model inference needs to be weighed with caution as accuracy remains low at this time of the year. It begins to improve significantly during June. A negative IOD increases the chances of suppressing monsoon bursts over the Indian sub-continent,” it said.
Meanwhile, IMD also said that the southwest monsoon has advanced into the remaining parts of the south Arabian Sea, Lakshadweep area, most parts of Kerala, some parts of south Tamil Nadu, some parts of the Gulf of Mannar, and some more parts of south-west Bay of Bengal on May 29.
The Northern Limit of Monsoon (NLM) now passes through lat. 12°N/ Long. 60°E, lat. 12°N/ Long. 70°E, Kannur, Palakkad, lat. 9°N/ Long. 79°E, lat. 8.0°N/ Long. 83°E, 12.5°N/90°E, 16.0°N/93°E, and 18.0°N/94.5°E.
“Conditions are favourable for further advance of southwest monsoon into some parts of central Arabian Sea, remaining parts of Kerala, some more parts of Tamil Nadu, some parts of Karnataka, some more parts of south and Central Bay of Bengal, some parts of the northeast Bay of Bengal and north-eastern states during next 3-4 days,” it said.