New Delhi. India Meteorological Department (IMD) today issued the second stage forecasts for the southwest monsoon rainfall for operational long range forecasts. IMD issued the first stage forecast on23rd April. IMD’s long range forecast for the 2010 south-west monsoon season (June to September) is that the rainfall for the country as a whole is likely to be normal. Quantitatively, monsoon season rainfall is likely to be 98% of the long period average (LPA) with a model error of ± 5%. The LPA of monsoon season rainfall over the country as a whole for the period 1941-1990 is 89 cm.

Update for the southwest monsoon season (June-September) rainfall over the country as a whole using a 6-parameter ensemble statistical model with a model error of ± 4% which include Northwest India , Northeast India , Central India and South Peninsula Andhra Pradesh, Karnataka, Tamil Nadu, Kerala, Lakshadweep and Andaman and Nicobar Islands .Forecasts for the monthly rainfall over the country as a whole for the months of July & August using separate principle component regression models with a model error of ± 9% and forecasts for the southwest monsoon season (June-September) rainfall for the four broad geographical regions of India using separate multiple linear regression models with a model error of ± 8% have been included in the second stage forecast.

IMD has also generated experimental forecast for the 2010 southwest monsoon rainfall based on the IMD’s dynamical forecast system (Seasonal Forecast model of the Experimental Climate Prediction Centre (ECPC), USA). The forecast was generated using observed global sea surface temperature data of May. The experimental forecasts from majority of the statistical and dynamical models suggest normal to above normal monsoon season rainfall over the country as a whole.

Regarding onset and Advance of Monsoon 2010, IMD informs that associated with the formation of cyclone “LAILA” over Bay of Bengal, southwest monsoon set in over Andaman Sea around 17th May, 3 days before its normal date. Subsequently monsoon reached Kerala on31th may, just one day before its normal date and advanced over northeastern states by 2nd June. With onset of monsoon over Kerala, another cyclonic storm (“PHET”) formed over the Arabian Sea and this delayed further advancement of the monsoon across west coast by about one week. Around 6th June, the monsoon got activated and by middle of June, it covered nearly half of the country. As on 24th June, the northern limit of monsoon (NLM) continues to pass through Lat. 22.0 N/Long. 60.0 E, Lat. 22.0 N/ Long. 69.0 E, Rajkot, Ahmedabad, Indore, Seoni, Pendra, Ambikapur, Daltonganj, Gaya, Muzaffarpur and Raxaul.

The cumulated seasonal rainfall over the country as a whole during the period 1-24th June is 89% of LPA. The El Nino conditions over equatorial Pacific that started in the mid June 20089 peaked in December and dissipated during early May, 2010. Since then, ENSO-neutral conditions are prevailing with negative SST anomalies observed over the equatorial Pacific from the middle of May. The latest forecasts from a majority of the dynamical and statistical models indicate continued and rapid cooling of the equatorial Pacific to below La Nina thresholds. There is very high probability (about 60%) for the La Nina conditions to develop during the monsoon season, which favours stronger than normal monsoon.

Recent forecasts from some coupled models suggest possibility of the development of a weak positive Indian Ocean Dipole event during the 2010 monsoon season, which may not have much impact on the Indian monsoon.

Rainfall over the country as a whole for the 2010 southwest monsoon season (June to September) is likely to be normal. Quantitatively, monsoon season rainfall for the country as a whole is likely to be 102% of long period average (LPA) with a model error of ± 4 %.

Rainfall over the country as a whole in the month of July 2010 is likely to be 98% of LPA and that in the month of August is likely to be 101% of LPA both with a model error of +9%.

Over the four broad geographical regions of the country, rainfall for the 2010 Southwest Monsoon Season is likely to be 102% of LPA over Norht-West India, 103% of LPA over North-East India, 99% of LPA over Central India and 102% of LPA over South Peninsula, all with a model error of ± 8 %.