Next ‘low’ in Bay may materialise in a week’s time

Wind-field projections by the India Meteorological Department (IMD) suggest that a cyclonic circulation/low-pressure area may be in the making along the East Coast in about a week’s time.

This corroborates the outlook by the Climate Prediction Centre of the US National Weather Services of a rain-driving system developing in the Bay of Bengal that could likely revive the monsoon.

Differing outlook

The two national forecasters, however, differ in terms of their choice of the exact location of genesis of the system, which is crucial from the viewpoint of the prospects of the monsoon.

The US agency has been pointing to a location off the Andhra Pradesh coast until Tuesday, which is per its latest available forecast.

As if on cue, a rudimentary circulation popped up on Wednesday morning over the South-West and and adjoining West-Central Bay off North Tamil Nadu and South Coastal Andhra Pradesh coasts. But the IMD predicts the ‘low’ will materialise at a different location, and is pointing instead to the seas off the Odisha coast and its neighbourhood.

This morning, the feeble offshore trough extending overnight from the Karnataka coast to the Kerala coast has persisted. The strength of the offshore trough is a proxy for the overall health of the monsoon. The offshore trough receives the moisture from the Arabian Sea, which is forced by the westerly to southwesterly winds against the heights of the Western Ghats to precipitate as rain along the coast.

Troughs in disarray

The offshore trough along the West Coast, and the land-based trough stretching diagonally across the plains of North India, are the two principal features that sustain monsoon rains over the country. Currently, the offshore trough is weak and lies in a truncated form from Karnataka to Kerala. When fully active, it straddles the entire West Coast lying extended from South Gujarat to Kerala.

The land-based trough over Central India has retreated to the North taking the rains along with it, and is heading for the Himalayan foothills, weakening the monsoon over the rest of the country.

Only the next ’low’ in the Bay, as and when it materialises, can bring the trough back with its south-eastern end pinned down to the centre of the ’low’ in the Bay and the other lying diagonally across in West Rajasthan.

This morning, a pre-existing intensified ’low’ over East Uttar Pradesh and adjoining Bihar continued to power the monsoon across the limited swathe of the Himalayan foothills and adjoining plains.

The land-based trough that packs this ’low’ lies extended from Punjab and runs across Haryana, West Uttar Pradesh and the hills of Bengal and Assam.

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