The Hindu Business Line : Bay likely to host last SW monsoon `low' this week

The deep depression in the east central Arabian Sea, remnant of tropical cyclone Mukda, underwent two rounds of weakening overnight and lay as a `low' around the same place as the previous day.

The counterpart `low' in east India also weakened into a `low' over Bihar and the adjoining areas, an update from the National Centre for Medium Range Weather Forecasting (NCMRWF) said.

LAST SYSTEM

The Bay of Bengal is busying up to host a migrant `low' in another two to three days' time. This could well be the last in the series to roll across the Bay this season, said Dr Akhilesh Gupta of the Department of Science and Technology. The southwest monsoon should normally end on September 30.

SURGE IN SOUTH

There's a fresh surge from the south in the inter tropical convergence zone (ITCZ), the band of low-pressure area encircling the globe. It has dovetailed with a strong flow passing over Kerala and south Tamil Nadu. The resulting wet session is set to prolong for at least another 24 hours in these regions.

This apart, a north-south trough of low pressure lies along the Tamil Nadu coast. This will bring fairly widespread rainfall across the rest of Tamil Nadu and into Rayalaseema over the next two days.

HEAVY FALLS

The `low' in the east will bring widespread rainfall with isolated heavy to very heavy falls over Bihar, sub-Himalayan West Bengal, Sikkim, Assam and Meghalaya for the next two days. Fairly widespread rainfall is also likely over east Uttar Pradesh and Jharkhand.

In the west, Kerala, Lakshadweep and the Andaman and Nicobar Islands are likely to receive isolated heavy to very heavy falls.

Meanwhile, the monsoon has further withdrawn from some parts of Jammu division, entire Punjab, most parts of Haryana (including Delhi and Chandigarh) and West Rajasthan and some parts of east Rajasthan.

On Monday, the withdrawal line passed through Jammu, Chandigarh, Delhi, Ajmer and Barmer.

Model predictions also suggest that the monsoon may further withdraw from some more parts of Northwest India during the next 24 hours.

ANTI-CYCLONE

Progressive withdrawal of southwest monsoon will bring the `big brother' anti-cyclone extending reach into south, pushing the ITCZ also along. Easterly flows to the south of the anti-cyclone will synchronise with the `low frequency mode' of rain pulses to set up the northeast monsoon in the peninsula, said Dr Gupta.

This will be preceded by the calibrated reduction in wind shear values over the Bay (wind shear inhibits cyclone formation) and gaining of depth by the easterlies. These features are pre-ordained and must settle into ideal slots for northeast monsoon to engage into top gear.

October 15 is the approximate timeline for all this to happen, said Dr Gupta.

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