A below-normal rainfall regime would prevail over the Indian subcontinent and South-East Asia until June 11, according to the Climate Prediction Centre of the US National Weather Service.

This assessment is based on expected delay in the movement of the all-important wet phase of the Madden-Julian Oscillation (MJO) wave across the Indian Ocean.

Dry MJO rules

Model are split on the MJO wave movement over the next two weeks. Only European Centre for Medium-Range Weather Forecasts and the Japanese Met Agency ensemble show its propagation across the Indian Ocean during this week. The Global Ensemble Forecast System maintains a more stationary MJO signal over Africa and the West Indian Ocean, which is seen extending the below-normal rainfall regime over India.

Suffice to say that an alternating dry phase of the MJO wave currently sitting over the region is generating searing heat over many parts of the country, the US agency said in an update. According to its forecast, the best hope for a favourable phase of the MJO to come into West Indian Ocean and adjoining South Arabian Sea is between June 5-11, triggering the monsoon onset over Sri Lanka.

Here, the monsoon would have been delayed by more than 10 days (the usual date of onset for the island nation is May 22). It usually takes around a week for the monsoon to reach the Kerala coast in India.

Likely onset date

Hence, it is likely that the date of June 6 set by India Met Department (IMD) with a model error of +/-four days, may get shifted to the upper margin of the elongated onset window. Additionally, the US agency hinted at a low risk of tropical cyclone formation over the Arabian Sea during the week from June 5 to 11. The MJO is known not just for setting up monsoon onsets but also rearing cyclones.

A cyclone during the onset phase has become more of a rule than exception these days. It can disrupt the monsoon flows and weaken them if it tracks away to Yemen/Oman, as has happened in the recent past. Meanwhile, the IMD has maintained this (Thursday) morning its outlook of conditions turning favourable for the monsoon onset over the Maldives-Comorin and parts of South Bay of Bengal during the next two days.

Widespread rainfall has been forecast over the Andaman & Nicobar during the next four days. Fairly widespread to widespread rainfall with isolated heavy falls is over the hills of Bengal, Sikkim and the North-Eastern States. Heat wave to severe heat wave conditions would over many parts of Vidarbha; in some parts over Madhya Pradesh; and isolated over Haryana, Chandigarh, Delhi, Rajasthan and Uttar Pradesh during next two to three days.

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