NEW DELHI, APRIL 14: Ahead of this week’s official April forecast for the monsoon by the India Meteorology Department (IMD), the US-based International Research Institute for Climate and Society (IRI) has said there is hope for good rains in the first half of the four-month monsoon season beginning June. The rainfall intensity may taper off in the last two months of the season.

The IRI map shows that in the first two months of the monsoon season, there will be good rains in the southern peninsula and parts of central India. In August-September, apart from peninsular India, there will be good rains in Gujarat and parts of Rajasthan and in the plains of the eastern Himalayas.

There is only a distant possibility of the spoilsport El Nino (warming of the Pacific water above normal) emerging in the period in the Nino 3.4 region — the region in the Pacific which influences Indian monsoons. In fact, the IRI sees the presence of the opposite phenomena La Nina (cooling of the Pacific waters below normal). Historically, La Nina causes good rains.

But La Nina is on a weakening trend. According to IRI, the 85% to 75% probability of La Nina in April and May would come down to 60% to 50% in June, the first month of the monsoon season. In July, the probability estimate remains in the range of 50% to 40%. In September, the last month of the monsoon season, the probability of La Nina would come down to 35% to 30%. But the El Nino factor is seen low at 5% to 20% in the monsoon period, while neutral condition could range from 5% to a maximum 50%.

Given the gradual decline of the La Nina factor, the good rains in the first two months of the monsoon season may taper off towards the end. There is also a possibility of early arrival on the southwest monsoon, sometime in May due to the higher influence of the La Nina factor. The IRI is slated to update its forecast on April 17.

But the US-based Climate Prediction Center (CPC) of the National Centers for Environmental Prediction (NCEP), confirming the gradual decline of the La Nino factor, said: “La Nina is expected to continue for the next three months... Nino 3.4 region indicate La Nina will become weak and persist through May-June-July 2008.” La Nina has already caused heavy rainfall over Indonesia.

According to IRI, western equatorial Indian Ocean has below normal temperatures while the eastern part has temperatures above the normal. The below normal temperature conditions in western Indian Ocean is likely to weaken slowly.