June and September are likely to witness above normal rainfall during the 2018 monsoon, while July and August — normally the rainiest — could disappoint, according to private forecaster Skymet.
The chances of normal to above normal rainfall is as high as 90 per cent during the first month of June, while September does not lag too far behind with 80 per cent probability.
According to Skymet, June is likely to deliver 111 per cent of the long period average (LPA) of 164 mm, while September could yield 101 per cent. Probability of above normal at 60 per cent is highest for June.
July is seen as falling short by three per cent of the LPA of 289 mm, while August would be even more so with a shortfall of four per cent compared to the LPA of 261 mm.
Weaker La Nina
Giving a background analysis, Jatin Singh, CEO, Skymet, said that weak La Nina conditions are prevailing over the Pacific Ocean and most likely, the transition of La Niña to ‘neutral’ conditions would take place during March to May.
Forecasts show that by during May-June-July, there is over 60 per cent chance of neutral, 24 per cent chance of a La Nina and 14 per cent chance of an El Nino panning out in the Equatorial Pacific.
In fact, weathermen are of the view that pre-monsoon rainy season would be slightly below normal, paving way for intense heat before the onset of the monsoon.
Dipole effect
The Indian Ocean Dipole (IOD) which mimics the El Nino-La Nina in the Indian Ocean marked by see-sawing of sea-surface temperatures is in the negative phase but within neutral limits currently.
However, weather models indicate that IOD would possibly shift near to normal during the second half of the monsoon. Warming up of the West Indian Ocean has been found to drive a successful monsoon in India.