The official weather forecasting agency, India Meteorological Department (IMD) has said that the countrywide rainfall in the four-month monsoon season, beginning June would be 99% of the long period average (LPA) rainfall for the period which is 89 cm.

The forecast is subjected to a model error of +/-5%.

Making this initial forecast for the South-West Monsoon, IMD said that it would be “near normal” rainfall as it has revised its categorization of rainfall basing on 1901-2005 data. In the revised categorization there is no normal rainfall. Rainfall in the range of 96% to 104% of the LPA is termed near normal, that in the range of 90% to 96% of the LPA is termed below norm and that below 90% of the LPA is termed deficient.

Rainfall in the range of in the range of 104% to 110% of the LPA is termed above normal and that above 110% is termed excess.

The Union Minister for Science and Technology and Earth Sciences, Kapil Sibal releasing the forecast said, “the presence of La Nina factor (cooling of Pacific waters below normal) would boost the prospects of good monsoon rains. The recent global dynamical and statistical models say that La Nina will become weak but persist for the next three months.”

The Indian Express and The Financial Express on April 15 quoting IRI data had said La Nina would cause good rains in the first two months.

Sibal said that IMD while making its forecast had taken help of both statistical and dynamical models. The dynamical models works well for peninsular India and northeastern region.

The leader of the monsoon forecast team, M Rajeevan said that a set of 5 predictors were used for making this initial forecast like North Atlantic sea surface temperature in December and January, equatorial southeast Indian Ocean temperature in Feberuary and March, east Asia mean sea level pressure in February and March, north-west Europe land surface air temperature in January and equatorial Pacific warm water volume in February and March.

The IMD would consider another set of 6 predictors while making the final forecast for the season in June. In May the IMD would predict the date of arrival of the South-West Monsoon at the Kerala coast.

Global climate change and its impact on Indian weather and monsoons is the issue which Indian meteorologists are exploring to understand. In last March there was unusual heavy rains in the four southern states ? Andhra Pradesh, Karnataka, Kerala and Tamil Nadu, causing damage to the standing crops. In Tamil Nadu the rainfall was in excess of 801%, that in Kerala in excess of 469%, that in Karnataka in excess of 1666% and that in Andhra Pradesh in excess of 811%. This year’s March rainfall was a all time high record in Tamil Nadu, Karnakata and Kerala since 1875, while in Andhra Pradesh it was the second highest since 1875.

There was practically no winter rains over north and northwest India in 2007-08, but there was a sudden spurt of heavy rains and thundershowers in the region on April 4, 2008 leading to cloudy weather for the next three days. In past there has been cases of sudden spurt in day temperatures in early February causing damage to wheat crop.