Monsoon watchers train focus on Arabian Sea as ‘low’ brews

A low-pressure area spinning up over Lakshadweep expectedly by Thursday could stir up the Arabian Sea and nearby Indian Ocean for the build-up for monsoon onset.

India Met Department is set to announce on Friday the date for the onset along the West Coast. Expectations are rising in terms of what looks like an early onset this year. The normal date is June 1.

Rain wave The US Climate Prediction Centre has picked up a wave of rainfall sitting around Sri Lanka and south India with a core sitting over equatorial Indian Ocean.

During the next two weeks, a wave of enhanced convection would move across the Indian Ocean towards the maritime continent (Indonesia, etc). Dynamical models indicate that this movement will be manifest especially during the week starting Wednesday.

Significantly, the US agency suspects this wave could increase the odds for a likely storm over the north Indian Ocean (comprising the Arabian Sea or the Bay of Bengal). During this period, the cross-equatorial monsoon flows are shown picking up speed both off the Somali coast as well as across the southern Bay of Bengal.

Storm likely? A few models indicate that the building ‘low’ over Lakshadweep would move north towards the Mangalore coast early next week and start growing in intensity.

From here, it would head towards the central Arabian Sea (away from the west coast) only to be guided back towards the coast for a landfall over Gujarat. This would happen under the influence of a western disturbance digging deep to the south into central Arabian Sea, forecasts indicate.

The rains will get driven into Rajasthan and across the border into Karachi. The whole of the peninsular India is likely to be brought under a welter of wet weather from the weekend, heavier towards the southwest coast (Kerala and neighbourhood) to start with.

But odds (notably outlook by the European Centre for Medium-Range Weather Forecasts) also favour a twin circulation over southwest Bay of Bengal travelling northeast to set up a storm on the east coast.

Onset dynamics The moot question these developments throw up is whether these would lead to an early onset of the monsoon. One enabling factor is the active state of the northwest Pacific, which is forecast to host a couple of typhoons (cyclones) in the intervening period.

These will help pull the monsoon across the Indian Ocean since the two oceans form inseparable parts of the single South-West monsoon system.

While super typhoon Noul has spun away towards Japan, successor typhoon Dolphin is currently tracking to the east of the Philippines and south of Japan. A third strong typhoon is forecast to brew in the northwest Pacific early next week, which will have a say on how Arabian Sea and Bay of Bengal would behave, and by extension, on the monsoon onset dynamics.

COMMENT NOW