The low-pressure area forming over the South-East Bay of Bengal tomorrow is seen flourishing on the back of strong south-westerly flows generated by a twin system developing just South of the Equator off the West Coast of Indonesia, with its clockwise movement of air and moisture around it. In contrast, the Bay system has winds moving in an anti-clockwise direction as they do in the region above the Equator (Northern Hemisphere). It is perfectly aligned in a giant ’S’ format to receive the flows below the Equator (Southern Hemisphere) blowing from a typical south-westerly direction. 

Eyeing Myanmar for landfall? 

Numerical weather predictions by India Meteorological Department (IMD) guides a powerful cyclone developing from the ‘low’ away from the East Coast of India to the South of Myanmar by May 13. The European Centre for Medium-Range Weather Forecasts and the Global Forecast System of the US Climate Prediction Centre see it blasting into the West Coast of Myanmar. The ‘low’ will intensify into a depression becoming cyclone Mocha over Central Bay. Till then, it would have travelled in an almost northerly track. Later, it would come under the influence of a western disturbance moving perpendicular to it from North-West India, dipping from Gangetic Plains into the Bay to scoop the cyclone and drag it to the East. 

Guiding western disturbance

In this manner, the cyclone would be forced to look away from the East Coast of India towards the Myanmar coast, as per numerical model predictions of the IMD and other leading global models. The causative western disturbance was parked over Afghanistan on Saturday morning, and will resume its journey towards North-West India and East India. This away-movement of the cyclone would prompt the dry weather-causing seasonal anticyclone in the lower levels to move in from across the Arabian Sea and start heating up the land over Central and North-West India. The region is already under a ‘heat-deficit’ with likely negative implications for the onset and progress of the impending South-West monsoon, which is already under an El Niño shadow. 

Dry third week of May

The Climate Prediction Centre of the US has already forecast that a regime of suppressed rainfall (dryness) may envelop Coastal and adjoining South Interior Karnataka, Kerala and adjoining South-East Tamil Nadu, which collectively act as the gateway for the monsoon, during May 17-23. The monsoon onset may be delayed over Sri Lanka, the penultimate pitstop, accordingly. Over mainland India and its neighbourhood, the monsoon begins earliest in Maldives (mid-May), followed by Myanmar, the Andaman & Nicobar Islands and Sri Lanka, before arriving over Kerala on the South-West coast. The Maldives is already reporting scattered rain with occasional heavy showers and thunderstorms on Saturday, with winds blowing at 27-47 km/hr with gusts of 83 km/hr thanks to the south-westerly flows triggered by the building activity in the Bay. 

Normal Myanmar onset?

Sri Lanka, too, is reporting similar climes, with forecasts indicating the possibility of several spells of showers and thundershowers over many parts of the island on Saturday afternoon and night and strong winds speeding up to 40-50 km/hr over the coasts along the West and the South. Meanwhile, Myanmar expects this year’s monsoon to be weak to moderate. The rains may set in over the southern parts during May 13-18 around the normal timeline, helped in so small measure by cyclone Mocha; over the Deltaic areas during May 19-24; and Central Myanmar from May 25-31. It expects two low-pressure areas to form over the Bay, with one intensifying into a depression (corresponding to the evolution of Mocha). 

Dry spell to follow

Even assuming that the cyclone brings the monsoon over Myanmar around the normal date, a dry spell may establish over the country on its trail, while Andaman & Nicobar Islands may have to wait for the build-up of favourable winds, clouds and moisture for rains to arrive. The Sri Lanka Meteorological Department expects the Bay cyclone to bring rain during the latter part of May. Significantly, the Sri Lankan national forecaster looks to the Bay to throw up another system (low-pressure area or depression) in early June, enhancing south-westerly monsoon flows across the island nation and adjoining India’s South Peninsula. Myanmar too has called for a second low-pressure area to develop in the Bay during the period.