‘Low’ to form over Bay by Tuesday, may bring north-east monsoon to South Peninsula

The building low-pressure area over Bay of Bengal may drive up a rainfall and lash initially the Sri Lanka and south Tamil Nadu coasts, says European Centre for Medium-Term Weather Forecasts. | Photo Credit: www.meteoblue.com

The first clear signal of a decisive shift in the weather over the South Peninsula has emerged, with India Meteorological Department (IMD) identifying an upper-air cyclonic circulation over the Gulf of Thailand as a potential harbinger of the ensuing north-east monsoon.

The development comes as the country draws towards the close of a south-west monsoon season marked by severe regional deficits, raising hopes of a second rainy season for the South Peninsula even as the retreating monsoon leaves its own unsettled legacy.

The Bay of Bengal appears poised to set the next phase in motion. The IMD expects the circulation over the Gulf of Thailand to move westward under the influence of accompanying easterlies and emerge over the Andaman Sea by Sunday. It may deepen as a low-pressure area over the adjoining south-east Bay of Bengal by Tuesday, potentially setting in motion a fresh round of rain-bearing weather system.

businessline had earlier flagged the developing circulation and arrival of easterlies over the Gulf of Thailand and the Andaman Sea. The developing system could provide the first significant building block for the north-east monsoon, which brings the principal rainy season to Tamil Nadu and parts of the South Peninsula. Its eventual arrival will depend on the evolution of the Bay system and establishment of seasonal easterly winds, but the ingredients for a transition are beginning to assemble.

The line of retreat of predecessor south-west monsoon was unchanged on Friday as it cut through Supaul, Ranchi, Sundargarh, Bargarh, Bijapur, Hyderabad, Belagavi and Panjim. Conditions are becoming favourable for further withdrawal from some more parts of East India and the northern peninsula, as well as many parts of North-East India, over the next three to four days, the IMD said.

The retreat over the mainland is coinciding with a fresh build-up of rain-producing systems over the surrounding seas. While the Bay of is preparing to host a new low-pressure area, the Arabian Sea side is also contributing to the unsettled weather pattern over the South Peninsula.

On Friday evening, a trough of low pressure extended from the Comorin area to North Interior Karnataka across Tamil Nadu and South Interior Karnataka. The configuration could help draw moisture inland and sustain cloud formation triggering rain, thunderstorms, lightning and gusty winds across parts of the region.

The wider circulation pattern is adding to the instability. The Gulf of Thailand system is being supported by cyclonic circulations over north Bangladesh and east Assam. Another trough extended from west Assam to Telangana across north Bangladesh, the hills of West Bengal and Sikkim, Jharkhand, Odisha and Chhattisgarh.

Together, these features may keep the weather volatile over the South Peninsula into next week. The emerging pattern could help prepare the ground for the north-east monsoon around its normal time, although the actual onset will depend on the subsequent evolution of the circulation and establishment of seasonal flow.

The IMD has forecast isolated heavy rainfall is likely over Kerala and Mahe, and Tamil Nadu, Puducherry and Karaikal on Saturday as well. Isolated to scattered rainfall is likely over Coastal Andhra Pradesh and Yanam, Coastal Karnataka, Rayalaseema, and Tamil Nadu, Puducherry and Karaikal for six more days. South Interior Karnataka may receive similar rainfall for two more days, with activity returning on Wednesday and Thursday.

Lakshadweep is expected to see isolated to scattered rain for five days from Sunday. Kerala and Mahe are in line for a more persistent spell, with fairly widespread to widespread rainfall forecast to continue for another six days. Lakshadweep, too, is likely to experience fairly widespread to widespread rain on Saturday.