The Hindu Business Line : Monsoon negotiating kerb as it prepares to sign off

The southwest monsoon, now in its fag end, has been vigorous over Assam and Meghalaya and active in Nagaland-Manipur-Mizoram-Tripura during the 24 hours ending on Friday morning.

The causative upper air cyclonic circulation may stir up weather over the northeast for another 24 hours before gradually fading out.

PEAK ACTIVITY

But during peak activity, immediately after crossing in from the Bay of Bengal the week before last, it presided over sustained heavy downpours and some of the worst flooding witnessed over the southern peninsula.

After being subsumed by an intervening westerly trough and driven north-northeast, it gradually started weakening but still was able to unleash heavy rains along the way over Uttar Pradesh, Bihar and the rest of east India.

On Friday, however, a trough extending south from this rain-generating system ran down from Sikkim to the Bay of Bengal, an update from the National Centre for Medium Range Weather Forecasting said.

The wet session in the northeast will henceforth rally around this trough formation, the NCMRWF added.

Weather is likely to remain mainly dry over the north, west, central and adjoining peninsular India during the next five days.

The NCMRWF has now assessed that the formation of a cyclonic circulation over north Andaman Sea and adjoining areas may happen around Sunday. The system may undergo a round of intensification.

The US Naval Fleet Naval Meteorology and Oceanography Centre too agreed with the outlook, though not overly suggesting any significant intensification.

TRANSITION PERIOD

The European Centre for Medium-Range Weather Forecasts sees the Bay of Bengal in a state of flux throughout the week. The FNMOC sees the southwesterly flows over the peninsula being gradually replaced by easterlies in what could be the transition into the winter monsoon (northeast monsoon).

But the easterly flows can pick speeds only with the arrival of the seasonal anti-cyclone over northwest India and its setting in a manner that the northeasterly flows along its southern flanks rub off their effect on the monsoon easterlies.

The core of the anti-cyclone is shown as sitting over north Arabian Sea, West Asia and Pakistan by the end of next week.

It would have to move further east to find a semi-permanent perch over northwest India. But this can take time since this anti-cyclone is massive in size extending from Africa and moves very slowly.

The US National Centres for Environmental Prediction sees clear signals of a likely onset of northeast monsoon during the week starting October 17.

An easterly rain wave is predicted to sit along a southwest-to-northeast axis extending from north Sri Lanka and adjoining southeast coastal Tamil Nadu to central Bay of Bengal.

The run-up to this (October 9 to 16) would see scattered showers breaking out over the peninsula from Bay activity even as the weather settles in the northeast.

WIDESPREAD RAIN

An India Meteorological Department has forecast fairly widespread rainfall with isolated heavy falls over the North-eastern States during the next 24 hours.

Satellite images on Friday showed convective clouds over parts of south Andaman Sea, Nagaland, Manipur, Mizoram and Tripura.

The three days ending Wednesday next would see scattered rainfall over south peninsular India. The southwest monsoon is likely to withdraw from the remaining parts of northwest India and some parts of east and central India during this period.

An update from the Chennai Met Centre said that rainfall occurred at a few places over north interior Karnataka during the 24 hours ending Friday morning.

Isolated rainfall occurred over Tamil Nadu, Andhra Pradesh, coastal and south interior Karnataka. Dry weather prevailed over Kerala and Lakshadweep.

Forecast for the next two days said that rain or thundershowers are likely at a few places over Karnataka, coastal Tamil Nadu and Puducherry. Isolated rain or thundershowers are likely over interior Tamil Nadu, Kerala, Lakshadweep and Andhra Pradesh.

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