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Vinson Kurian

Thiruvananthapuram May 23 India Meteorological Department (IMD) said on Wednesday that the onset of the southwest monsoon over Kerala was not likely to take place during the next three to four days.

IMD said in a special bulletin that, this year, monsoon set in over Andaman Sea and southeast Bay of Bengal on May 10, about a week earlier than the normal. On May 14, the IMD issued a forecast for onset of monsoon over Kerala on May 24 with a model error of plus or minus three days.

However, subsequent to onset of monsoon over Andaman Sea, a cyclonic storm (Akash) formed over east-central Bay of Bengal. It moved north-northeastwards and crossed the Bangladesh coast on May 15. This has disrupted the entire monsoon flow.

The monsoon is slowly organising back after this disruption. During last few days, a weak cross equatorial flow has established over the Arabian Sea with associated thin clouds.

However, its strengthening and progress towards the west coast of India has been inhibited due to development of an anomalous low-level circulation over west-central Arabian Sea and persistence of a westerly trough over Indian region.

Because of the above meteorological conditions, the monsoon onset over Kerala is not likely during the next three-four days. Monsoon is a planetary scale system and exhibits sporadic variations. IMD is constantly monitoring its progress and updates will be issued regularly.

The westerly trough rolling in from the northwest border is the predominant system dictating weather to most parts of the country currently. Its big amplitude gives it the wherewithal to sit over the landscape covering Pakistan and northwest India as a semi-permanent system (an extended tenure of 7-10 days against the normal of three-four days).

Westerly systems

Approaching westerly systems have interfered with the monsoon onset process in the past, but have hardly matched the near-total demolition of rare convergence by disparate weather models on earlier-than-normal onset forecast, as in the instant case.

Not only will the westerly trough send the monsoon onset matrix for a toss, it will also pump in moisture to set off non-seasonal rain showers and thunderstorms creeping over the Western Ghats into Gujarat and even Rajasthan. "So much so, people will be forgiven for thinking that onset has happened elsewhere," said a meteorologist.

"Of course, this far north, this would not be the start of monsoon, at least not with an upper westerly trough (hosting one or more western disturbances) hovering nearby," said Mr Jim Andrews of AccuWeather.com.

IMD has forecast rain or thundershowers for Kerala, Lakshadweep, Tamil Nadu, coastal Andhra Pradesh and coastal Karnataka over the next few days. Going further forward, it sees an increase in rainfall activity along the west coast from the weekend.

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Monsoon may be delayed by 3-4 days

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