The country will have normal monsoon this year. Releasing Long Range Forecast for coming June to September period, Union Minister for Science and Technology and Earth Sciences, Shri Pawan Kumar Bansal said, “ The rainfall for the country as a whole is most likely to be Normal i.e. 96-104% of Long Period Average (LPA). There is very low probability for season rainfall to be deficient (below 90% of LPA) or excess (above 110% of LPA). Quantitatively, monsoon season rainfall is likely to be 98% of the LPA with a model error of + 5%. The LPA of the season rainfall over the country as a whole for the period 1951-2000 is 89 cm.”
This was the first stage of the forecast strategy by India Meteorological Department (IMD) and the second stage forecast will be done in June 2011. Along with the update forecast, separate forecasts for the monthly (July and August) rainfall over the country as a whole and seasonal (June-September) rainfall over the country as a whole during the second of the season (August + September) will be issued in July and that for September will be issued in August.The Long Period Average (LPA) of the southwest monsoon season rainfall over the country as a whole for the period 1951-2000 is 89 cm. The first long range forecast for the southwest monsoon season (June-September) rainfall is issued in April and the forecast update is issued in June.
From 2007 onwards, IMD has been using the two statistical models for preparing quantitative and probabilistic forecasts of the southwest monsoon rainfall (June- September) for the country as a whole. They are a 5- parameter statistical ensemble forecasting system requiring data up to March, for the first forecast in April and a 6- parameter statistical ensemble forecasting system requiring data up to May for the forecast update in June. Three of these 6- parameters are same as that used for April forecast.
The El Nino conditions that were originated since June 2009 peaked in December 2009.After that they started to weaken to reach ENSO-neutral conditions in May 2010. This continued till mid June when weak La Nina conditions emerged. The La Nina conditions strengthened subsequently and become moderate to strong during mid-August 2010 to early February 2011. The La Nina conditions since have weakened to weak to moderate strength as of mid-March 2011. The latest forecasts from a majority of the dynamical and statistical models indicate strong probability for the present La Nina conditions to continue till June. Subsequently the La Nina conditions are expected to weaken further to reach ENSO- neutral conditions. However, it may be mentioned that the climate forecasts prepared at this time of the year has large uncertainty.
In addition to ENSO events, other factors such as the Indian Ocean Sea surface temperatures (SSTs) have also significant influence on Indian monsoon. Recent forecasts from some coupled models suggest possibility of the development of a weak negative Indian Ocean Dipole event during the second half of the year, which may not have much impact on the Indian monsoon.
As the extreme sea surface temperature conditions over Pacific and Indian oceans particularly ENSO conditions over Pacific (El Nino or La Nina) are known to have strong influence on the Indian summer monsoon, IMD is carefully monitoring the sea surface conditions over Pacific and Indian oceans.