The India Meteorological Department (IMD) has forecast near normal rainfalls in India during the 2008 south-west monsoon season (June to September).

Quantitatively, the monsoon season rainfall is likely to be 99 per cent of the long period average with a model error of ± 5 per cent. Kapil Sibal,  union minister for science and technology and earth sciences, siad in a press conference that the  long period average rainfall in India from 1941 to1990 has been around 89 cm

During August 2007, La Nina conditions had developed over the equatorial Pacific with colder than normal sea surface temperatures (SST). However, during  recent weeks, negative SST anomalies weakened across the central and east-central equatorial Pacific.

During March 2008, La Nina conditions declined to moderate-strength. The recent dynamical and statistical SST forecasts indicate La Nina will become weak and persist during the next three months. Thereafter, there had been considerable spread and uncertainty in the forecasts of La Nina conditions.

IMD follows a two-stage forecast strategy for long-range forecasts of the south-west monsoon rainfall over the country as a whole. The first long range forecast for the south-west monsoon season (June-September) rainfall is issued in April and the forecast update is issued in June.

Last year, IMD introduced the following new statistical models for forecasting south-west monsoon rainfall (June – September) for the country as a whole:

A 5- parameter statistical ensemble forecasting system requiring data up to March, for the first forecast in April.

A 6- parameter statistical ensemble forecasting system requiring data up to May for the forecast update in June.

The same forecasting system is used for preparing the forecast for the 2008 South-west monsoon rainfall. 

Operational Statistical Forecast System

In the IMD's Ensemble Statistical Forecasting system, the following 8 predictors are used, out of which the first 5 predictors are used for the April forecast.