The Hindu Business Line : Monsoon exits from most of north-west

Thiruvananthapuram, Sept. 29 The south-west monsoon has entered the withdrawal phase, with the India Meteorological Department (IMD) confirming that the seasonal weather system has signed off from large parts of the north-west.

The withdrawal ‘arc’ advanced past Jammu and Kashmir, Himachal Pradesh, Punjab, Haryana, most parts of North Arabian Sea, Rajasthan and Uttarakhand, some parts of west Uttar Pradesh and Gujarat.

Configured along a northwest-to-north-to-southeast axis, the arc will sweep into central India, more parts of Arabian Sea, the Bay of Bengal and the peninsula in phases. It passed through Naliya, Deesa, Sawai Madhopur, Dholpur, Bareilly and Mukteshwar on Monday.

A wind analysis in upper atmospheric levels showed dry westerlies to north-westerlies invading the Gujarat-Rajasthan border. But a weak easterly wind regime was holding on gamely to the east, watched by Sunday’s feeble ‘low’ over Bangladesh and adjoining Gangetic West Bengal, though less marked a day after.

FRESH CIRCULATION

This circulation has spawned a ‘mirror feature’ over Bihar and adjoining Jharkhand in line with forecasts by some international models. This will help carve out a corridor of wet weather along the Himalayan foothills into adjoining Uttar Pradesh.

The IMD sees fairly widespread rains breaking out over north Bihar, extreme north-east Uttar Pradesh, Sub-Himalayan West Bengal, Sikkim, Assam, Meghalaya, Nagaland, Manipur, Mizoram and Tripura with isolated heavy rains over north Bihar, Sub-Himalayan West Bengal and Sikkim.

In the mid-high levels, the two main circulation features driving the weather were the seasonal anti-cyclone extending into Rajasthan and, to the far-east, powerful storms in the Northwest Pacific basin. Super Typhoon Jangmi has weakened into a depression but Tropical Storm Mekkhala has spun up anew in the basin.

PENINSULAR WEATHER

The storm activity would, in turn, have a bearing on the easterlies and by extension the peninsular weather which would witness thunder storm activity until October 13. The seven-day forecast by the US National Centres for Environmental Prediction said rains aggregating to 7.5 cm are likely.

The Equatorial Indian Ocean has warmed up ahead of predicted convective activity and precipitation. The peninsular seas have cooled down northward from the extreme south-west and south-east. The Head Bay and the Northwest Arabian Sea sharing the same latitude are forecast to witness thunderstorm activity by mid-October.

The possibility of full-blown cyclones developing over these seas is being discounted for the time being. Meanwhile, the debate on ‘base La Nina’ state returning to the Equatorial Pacific has acquired a new sense of urgency with some forecasters zeroing in on an ‘evolving pattern.’

Closer home, the IMD said that current meteorological analysis and numerical weather prediction models suggested subdued rainfall activity or mainly dry weather conditions over north-west, west, central and peninsular India during the next four days.