The Hindu Business Line : Monsoon covers entire country with 5-day lead

Thiruvananthapuram, July 10 The southwest monsoon has in a ‘delayed push’ covered the remaining parts of Rajasthan on Thursday, thus bringing the entire country five days ahead of the normal schedule of July 15.

This milestone had been in the making for quite sometime with the seasonal weather system racing in with a record 15-day lead time. But, it squandered this advantage after its crucial southeasterly bearing gave way during the days that followed.

The southwest coast has since witnessed only localised heavy rains – the peninsular interior getting to see hardly any – as the Arabian Sea went into an enforced stupor. But the basic monsoon attributes, including the cross-equatorial flows, have largely held strong. The only exception was the winds, which, if not erring in direction, had simply failed to measure up in speed.

IOD WEAKENS

The Indian Ocean is currently in a positive phase of the Indian Ocean Dipole (IOD) which is monsoon-friendly, but the index used to measure the IOD has weakened considerably since its peak in early June, according to the Australian Bureau of Meteorology.

The IOD index is the difference between sea surface temperatures in the western and eastern tropical Indian oceans. A positive IOD occurs when the western basin is warmer than average and the eastern basin is cool and hence the IOD index is positive. Those models that forecast the IOD show it persisting but moderating further throughout the rest of the year.

Consensus forecasts are that the prevailing lull in the south would last for another eight to 10 days. Contrary to forecasts, the weak Madden-Julian Oscillation (MJO) wave of periodical planetary-scale anomalous precipitation has not been able to make much headway into the adjoining Arabian Sea.

This is now forecast by various models to get a move to the east and trigger some rain over a region spanning the Maldives and the Lakshadweep Islands and extreme south peninsular India from July 19-20. During this phase, a ‘low’ is forecast to develop in the southeast Arabian Sea, off the Kerala coast.

A forecast statement from the Climate Prediction Centre of the US National Weather Services on Monday and valid for 20 days said that weak MJO activity is forecast with wet conditions developing over the Indian Ocean. Almost all major weather models seemed to support this outlook.

A ‘low’ is seen materialising over the Head Bay of Bengal around the same time with a typical west-northwest track for lateral movement.

This would take the system and associated rain belt over central India, even dipping over west Madhya Pradesh and adjoining Gujarat.

The European Centre for Medium-Range Weather Forecasts too sees the southeast Arabian Sea buzzing during July 18 to 20 and the Bay stirring up in near unison. Joining this forecast ensemble is the US-based Centre for Ocean-Land-Atmosphere Studies (COLA) that saw these very scenarios unfolding during the nine days from July 18.

Meanwhile, Wednesday’s well marked ‘low’ over Jharkhand has weakened into a conventional ‘low’ and lay over East Madhya Pradesh on Thursday. It will trigger fairly widespread rainfall with isolated heavy to very heavy falls over Madhya Pradesh during the next two days.

The other upper air cyclonic circulation over West Uttar Pradesh had shifted base to northeast Rajasthan. Under its influence, fairly widespread rainfall with isolated heavy falls is likely over East Rajasthan during the same period.

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Monsoon stays muted over peninsula

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