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The current heavy to very heavy rainfall regime over Mumbai and its neighbourhood will in all probability be replicated over Central India and East-Central India over the next few days.
According to the European Centre for Medium-Range Weather Forecasts, the heavy rain belt is forecast to sit variously over Nagpur, Indore, Bhopal, Jabalpur and Kota before shifting to Allahabad, Lucknow, and Patna.
During this phase, areas to the North and South of this belt are likely to see just normal or even below-normal rainfall in a trend thought to be brought about by the ongoing positive phase of the Indian Ocean Dipole (IOD).
IOD Impact seen
The IOD is more or less the Indian Ocean version of the El Nino-La Nina phenomena in the Equatorial Pacific with a comparably more profound effect on a concurrent Indian monsoon.
When the western basin of the Indian Ocean warms up anomalously relative to the eastern basin, it is called a positive phase of the IOD. The exact reverse occurs during a negative phase of the IOD.
The positive IOD phase is widely thought to be beneficial to an ongoing Indian monsoon since it helps boost the process of convection and cloud-building. This is evident in the strong build-up of cross-equatorial monsoon flows over the Arabian Sea.
The India Meteorological Department (IMD) has said in its outlook that ‘rough’ to ‘very rough’ (waves rising 8-20 ft in height) conditions may prevail over the South-West and adjoining West-Central Arabian Sea during the rest of the week.
Poor wind direction
These represent sea areas where the westerly to south-westerly monsoon winds originate and ratchet up to peak speeds before lashing India’s West Coast.
While these winds have maintained their intensity and orientation along the northern parts of the West Coast (South Gujarat to Mumbai to Goa), it has not been the case with the rest of the coast from Mangaluru down to Kerala.
Winds here have been north-westerly, which does not help clouds to form and allows the summer sun to beat down on ground. This stretch has not seen any significant rain even as a deluge has crippled Mumbai and its neighbourhood and parts of Central India.
This is a scenario identified with a positive phase of the IOD, which delivers above normal rainfall over the central parts of the country right from the West to the East, and below normal rainfall to the North and South.
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