The South-West monsoon has advanced into parts of the South Arabian Sea, the Maldives, and the Comorin areas as well as some more parts of the South and East-Central Bay of Bengal.

Conditions are favourable for its further advance into more parts of these areas as well as over the North-East Bay of Bengal during the next two days, India Meteorological Department (IMD) said in an update.

On Thursday, the monsoon had checked into a region along an arc stretching from the West of Maldives and cutting through its middle atolls towards the East (away to the South-West of the Lakshadweep Islands) and some distance away from the South of Sri Lanka (where it should have reached by May 22) and onward across to South-West, East-Central and North-East Bay of Bengal.

Low-pressure area soon

A cyclonic circulation developing over the South-East Arabian Sea (off Kerala) around Monday next (June 5) is expected to herald the monsoon onset over Kerala subsequently.

The IMD expects this circulation to deepen as a low-pressure area, which would anchor the incoming monsoon flows, and set up what are likely seen as strong onset conditions along the Kerala coast.

Circulation over Bay

On Thursday, another cyclonic circulation lay to the other side of the peninsula over the East-Central Bay of Bengal off Myanmar.

Though this circulation may not get much traction in the Bay over the next few days, incoming flows from the Arabian Sea will trigger the formation of a compatriot ‘low’ here around the time its predecessor in the Arabian Sea gathers strength.

Perfect background

Simultaneous circulations over the Arabian Sea and the Bay set up the perfect background for the monsoon to prosper over mainland India. But the track of Arabian Sea ‘low’ needs close monitoring.

There are contrasting views, with some of the models taking it away from India to the disadvantage of the monsoon. Others point to a more orderly track along the West Coast.

Outlook for the first week

The IMD had said it expects below-normal rainfall during the first week of June (1-7) over the West Coast and East and North-East India and normal to above-normal for North-West and Central India (thanks to western disturbances).

Its extended-range weather forecast valid until June 7 had, in this manner, ruled out a full-fledged onset of the monsoon over Kerala during this period.

Heavy rain for Kerala

A five-day outlook predicted light to moderate to fairly widespread rain, thunderstorms, lightning, and gusty winds over Kerala, Lakshadweep, Coastal and South Interior Karnataka and isolated to scattered rain over Tamil Nadu and Andhra Pradesh until Monday.

Heavy rain is likely over Kerala, while it will be isolated over Tamil Nadu and Coastal Karnataka on Thursday.

Wind pattern to settle

The projected wind pattern valid until Tuesday does not indicate monsoon onset until Tuesday (June 6). Winds have to be westerly to south-westerly along the Kerala coast to declare the onset.

The brewing Arabian Sea ‘low’ will act as the ‘vortex’ for monsoon flows to rally around, and its strengthening from Wednesday (June 7) will likely lead to the onset in subsequent days.

The normal date of onset is June 1 with a standard deviation of seven days, but IMD’s long-range forecast expects this to be delayed this year until June 4, with a margin of ±4 days.

Satellite pictures on Thursday afternoon (June 1, conventionally the normal day of onset) showed intense convection (cloud building) over Coastal Karnataka, Goa, and off the coast of Kerala.