Monsoon may shift to north-east

Central and western India will continue to receive moderate to heavy showers over the next 4-5 days as the deep depression currently over the land tracks west-northwest initially. But the system may start weakening sooner than later and track more to the west to set up another wet spell over Gujarat and south-west Rajasthan. Mumbai is a little south of where the action is, but will still get rains.

There would be a marked reduction in rains over central India from around July 26, triggering a chain of events leading up to overall weakening of monsoon activity.

Break-monsoon signals


There is no official `break-monsoon' call yet, but some signature features - retreat of the monsoon trough to the Himalayan foothills, `segmentation' of south-westerlies and arrival of westerly trough over north India - are about to unravel.

Break-monsoon is manifest in the interruption of monsoon rainfall by spells of sparse rainfall during the mid-monsoon months of July and August over the plains of northern India.

This happens when a prevailing monsoon system moves from the plains in a northerly direction toward the sub-montane region of the Himalayas, taking the monsoon trough along with it.

This intra-seasonal recess in activity over central India and the northwest will see rains migrating to east and north-east India and along parts of the south-east coast.

The segmentation of the monsoon westerlies will see one branch extending straight over central India and further north, while the other will fork out over the peninsula and beyond. Kerala and Karnataka make gains from the latter branch.

This can also be extrapolated to a situation where monsoon rain gets shifted half way across the globe to the west Pacific. A building system in the west Pacific can appropriate the Arabian Sea flows and grow. On Tuesday, an incipient system was traced to the waters of the central Pacific.

FRESH `LOW'

Dr Akhilesh Gupta, lead operational forecaster and Adviser to the Ministry of Science and Technology, said that monsoon westerlies may start dominating the plains of north India from July 26, replacing the easterlies.

India Meteorological Department (IMD) sees a fresh `low' spinning up over north-west and adjoining west-central Bay of Bengal around July 24, though its orientation may just help entrench the weak monsoon conditions.

The European Centre for Medium-Range Weather Forecasting has reinstated its watch for this `low' in the Bay. But the system is tipped to travel north-northeast (away from central India) and might land up over the extreme east of the country. This `low' would combine with the itinerant westerly trough rolling into north India to trigger prolonged and widespread heavy to very heavy rains over east India, the entire Himalayan foothills and Nepal.

The evolving weather over the east will need to be closely watched since the region is vulnerable to flash-floods and landslides from sustained heavy rains.

But one stand-out feature of the macro weather situation is that the Arabian Sea flows are not forecast to weaken significantly, despite the contra-indicative signals obtaining over land, Dr Gupta said.

MONSOON REVIVAL

Strong flows might just help rub-off some activity over the Bay of Bengal, which can bring the seasonal monsoon trough back to its normal position, straddling the plains and eventually dipping into the Bay of Bengal system.

The break-monsoon ceases, and normal monsoon conditions are re-established, when the monsoon trough returns to the plains and intensifies. This occurs in association with a `low' developing in the Bay and moving toward the plains.

Meanwhile, an IMD forecast said that the deep depression over land would cause widespread rainfall with heavy to very heavy falls and isolated extremely heavy falls over Chhattisgarh and Vidarbha during the next 24 hours.

Fairly widespread rainfall activity with isolated heavy to very heavy falls is likely over interior Orissa and Telangana during next 24 hours. The heavy rain belt will shift to over Madhya Pradesh, where it will be active for the next two days.

Fairly widespread rainfall activity with isolated heavy to very heavy falls is also likely over Gujarat and Maharashtra during the next two to three days.

Heavy to very heavy rainfall has been forecast also over Madhya Maharashtra, Konkan, Goa and Marathwada, while it will be isolated heavy over coastal Karnataka and Kerala during the next two days.