India Meteorological Department (IMD) has said the South-West monsoon may enter Kerala late by three days (model error of ± 4 days) on June 4 while private forecaster Skymet Weather pushed the date back by three more days to June 7 (⍊3 days) after erstwhile cyclone Mocha disrupted incoming flows and swept away crucial monsoon moisture towards Myanmar. 

Mocha had erupted in landfall over the Myanmar coast on Sunday. businessline had reported on May 10 the monsoon is likely to be delayed by a few days in the wake of cyclogenesis and rapid intensification. At stake was its scheduled arrival of over the Andaman & Nicobar Islands, gateway for the monsoon in the Indian territorial waters over the Bay, around May 20. 

Twin cyclone Fabien

While the IMD did not expressly attribute the delay to Mocha, Skymet Weather pointed to twin cyclone Fabien just to South of the Equator, which will take at least a week to clear out. This storm is cutting into the cross-equatorial flows that normally help build the monsoon. This apart, an unfriendly high-pressure area (anticyclone) is looming large over the Arabian Sea.

Onset over the mainland has a standard deviation of seven days, Skymet said. In the last 10 years, the earliest arrival was on May 29 in 2018 and 2022, with the most delayed being on June 8 in 2019. The Climate Forecast System models suggest cross-equatorial flows strengthening and conducive sea conditions for the monsoon surge emerging around June 7. A lag of +/- 3 days is quite normal for the commencement of weather activity along and off the Kerala-Karnataka coast. 

Lag over Myanmar

Meanwhile, Myanmar, the penultimate stop, announced on Tuesday it expects the monsoon to set in over the southern parts by May 18, the outer extreme of the projected onset window of May 13-May 18. The normal date of onset is May 13. This lag is likely being carried forward as the monsoon plots arrival at its next stop over the Andaman & Nicobar Islands, followed by Sri Lanka.

Myanmar had given out the schedule as follows: the southern areas during May 13-18; the delta (May 19-24); Central Myanmar (May 25-31) and Northern Myanmar (June 1-6). During this phase, the monsoon would normally call in at the intervening Andaman & Nicobar Islands (around May 20) and Sri Lanka (May 25) before hitting mainland India along Kerala by June 1. 

This schedule is not likely to be met, as per the IMD forecast given out on Tuesday, since Mocha may have set the clock back by a few days. Incessant rain from the cyclone has cooled down parts of the Bay of Bengal but sea surface temperatures in the extreme eastern parts of the Andaman Sea, the Gulf of Martaban and Gulf of Thailand were at a steaming 31℃ on Tuesday.

Silent Bay of Bengal

None of the global models show development of any sea-based system that could accentuate the flows over the Bay to help with the onset over the Andaman & Nicobar Islands. Maldives, the earliest pit-stop for the monsoon, forecast continued scattered showers and thunderstorms and rough seas on Tuesday. The monsoon has not been declared officially yet over the southern atolls but west-to-northwesterly winds have notched up speeds of 21–37 km/hr with near-cyclonic gusts of 72 km/hr.