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Rain and thunderstorms lashed the South Peninsula and Sri Lanka on Tuesday evening as withdrawal of south-west monsoon remained on hold for another day. | Photo Credit: www.windy.com
The South-West monsoon showed little inclination to retreat on Tuesday, with its withdrawal line remaining unchanged from Monday even as heavy rain continued to sweep across the South Peninsula in what could be an increasingly wet run-up to North-East monsoon.
The India Meteorological Department (IMD) expects conditions to become favourable for withdrawal of the monsoon from more parts of East and North-East India and adjoining areas of north Peninsular India during this week and into next. But the transition could prove less orderly than usual, with the retreating monsoon and the advancing north-east monsoon potentially overlapping in time. The stakes are rising because a potentially important weather system is likely taking shape over the Bay of Bengal.
Heavy to very heavy rain lashed parts of Tamil Nadu, Puducherry and Karaikal from Monday to Tuesday, while heavy rain was also recorded over Rayalaseema, south interior Karnataka, Kerala and Mahe. These are precisely the regions that will form the core domain of the North-East monsoon in the weeks ahead; also where the just-concluded South-West monsoon has left significant rainfall deficits.
Several rain-producing features remained in place on Tuesday evening. Cyclonic circulations persisted over south coastal Odisha and adjoining north-west Bay of Bengal, the south-east Arabian Sea off the Kerala coast and north Tamil Nadu. A trough stretched from the Gulf of Mannar to Madhya Maharashtra across Tamil Nadu and interior Karnataka , helping sustain the moisture feed and unstable weather over the region.
The IMD expects this broad zone of unsettled weather to persist for the next few days, with isolated heavy rain , fairly widespread to widespread rainfall, thunderstorms, lightning and gusty winds likely across large parts of the South Peninsula. This continuing activity could, in turn, prevent the withdrawal of the South-West monsoon from making substantial further progress for a few more days.
The more consequential development, however, could come from the Bay. The IMD expects a cyclonic circulation to emerge over north Andaman Sea by Monday next. It could consolidate into a low-pressure area the following day and, if conditions remain favourable, intensify further into a depression over the central and adjoining south Bay of Bengal by around October 15, the normal onset date of the North-East monsoon.
A retreating South-West monsoon, a still-active rain-producing circulation over the Peninsula and a fresh Bay system developing close to the climatological onset date of the North-East monsoon could create a classic transition-season setup. The intensity of the ongoing spell is reflected in the rainfall totals recorded up to Tuesday morning. Tamil Nadu, Puducherry and Karaikal recorded some of the highest amounts, with Valparai Taluk Office and Valparai PAP receiving 12 cm each; followed by Chinnakalar (8 cm), Palacode and Burliar (7 cm each); and Thali, Uthagamandalam, Yercaud, Krishnarayapuram and Chamraj Estate (6 cm each).
In Rayalaseema, Royachoti recorded 9 cm, while Venkatagiri Kota, Arogyavaram and Penagaluru received 6 cm each. Punganur, Lakkireddipalle, Nambulipulikunt, Madanapalle and Santhipuram recorded 5 cm each .Kerala and Mahe saw 8 cm being reported at Neryamangalam ARG; 7 cm at Vellathooval AWS; and 5 cm each at Kurudamannil and Kanjirappally. South Interior Karnataka recorded 7 cm at Bargur; 6 cm each at H D Kote; the KSNDMC Campus; and 5 cm each at Begur and TG Halli HMS. Kollur in Coastal Karnataka received 5 cm.
The rainfall outlook for neighbouring Sri Lanka adds another dimension to the transition. Probabilistic multi-model ensemble guidance, based on dynamical models from 12 Global Producing Centres, offers no clear countrywide signal for October and November. The island therefore faces broadly equal chances of below-, near- or above-normal rainfall over the two months.
Western and Sabaragamuwa Provinces, along with Galle and Matara districts, have an increased likelihood of above-normal rainfall in October, while most of the rest of the country could see slightly above-normal rainfall. The signal strengthens for November, when most parts of Sri Lanka have an increased likelihood of receiving above-normal rainfall.
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