India Met Department suggests seasonal rains may unfold after a normal lapse of a fortnight after reaching Bay
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NIRMAL HARINDRAN/THE HINDU
The south-west monsoon may reach Kerala on May 27, five days ahead of normal and with a model error of ±4 days. It will bring seasonal rains to mainland India exactly a fortnight after unfolding over the extreme south-east Bay of Bengal and adjoining south Andaman Sea, its first port of call in territorial waters, as already forecast by the India Meteorological Department (IMD).
businessline had said in a report on Friday that monsoon winds had strengthened over the seas after turning south-west from the southern hemisphere and across the equator. Read here: https://www.thehindubusinessline.com/economy/agri-business/monsoon-winds-strengthen-over-seas-thunderstorms-loom-over-land/article69557108.ece
Earliest since 2009
If it arrives in Kerala as expected, it will be the earliest onset over the mainland since 2009, when it began on May 23, according to IMD). Onset dates in the past five years are: May 29 in 2022; May 30 in 2024; June 1 in 2020; June 3 in 2021; and June 8 in 2023.
Model error of 4 days on either side of May 27-mean suggests the season may unfold any day in between. If prospects of its propagation signalled by various models are anything to go by, chances this year are it can happen earlier than the mean date.
Upset clockwork
The timeline for the projected onset of the monsoon over Kerala (Arabian Sea side) also factors in a lapse of two weeks after the Bay arm locks into position. The clockwork precision with which this has traditionally occurred has been undone in recent times by global warming, which sets up early storms during the onset stage itself.
Early storms are often away-going and disrupt the orderly progression of the monsoon. Storms are guided towards outer seas or foreign land (Oman/Yemen in the Arabian Sea or Myanmar/Bangladesh in the Bay). Neither IMD nor any global forecast model sees the possibility of such a storm brewing this year, except a low-level circulation over the Bay that can help pull in the monsoon.
Helpful circulation
An upper air cyclonic circulation has been hovering over the south-east Bay and adjoining south Andaman Sea for the past couple of days. IMD expects it to descend to lower levels by May 19, when the monsoon will already have advanced into the Bay. Its internal dynamics might be just enough to push the monsoon towards onset, with or without a circulation this time round.
Above-normal
The IMD, in its first long-range forecast issued in April, said the country may see above-normal rainfall in the June to September season. Cumulative rainfall is estimated at 105 per cent (with a model error of ±5 per cent) of the long-period average of 87 cm. Typically, rain covers the entire country by July 8 before it starts withdrawing from North-West India around September 17.
Published on May 10, 2025