India Meteorological Department Forecast for Monsoon Onset over Kerala

The onset forecast model suggests that the monsoon onset over Kerala is likely to be on 30 May 2006, with a forecast error of ± 3 days. There is no one to one correspondence between monsoon onset date over Kerala and subsequent monsoon rainfall during the season (June to September) over the country as a whole.

Over the Indian mainland, south-west monsoon arrives by 1 June over south Kerala with a standard deviation of about 7 days. Slowly moving northwards along the western coast and northwestwards across central India, monsoon covers the whole country by 15 July. Monsoon arrives over Mumbai by 10 June and over Delhi by 29 June. During the last 50 years, the earliest monsoon onset over Kerala was on 14th May 1960 and the most delayed onset was on 18 June in 1972.

Last year, IMD had indigenously developed a new statistical model with 6 predictors to forecast the monsoon onset over Kerala. These predictors are: NW India Minimum Temperature, Pre-monsoon rainfall peak over south Peninsula, Outgoing Long wave radiation (OLR) anomaly over the Indo-China region, South Indian Ocean Sea Surface Temperature, South Indian Ocean lower tropospheric wind and Outgoing Long wave radiation (OLR) anomaly over South-west Pacific region. The statistical model has a forecast error of ± 3 days. Based on this model, in 2005, IMD issued a long range forecast for the monsoon onset over Kerala for the first time and it was proved correct. Last year, monsoon arrived over Kerala on 5 June as against the forecast of 7 June.

The same statistical model was used to prepare the long range forecast of monsoon onset over Kerala for this year also.

The weak El Nino conditions that prevailed in 2004 abruptly ended in the first half of 2005. Sea surface temperatures were close to normal over the equatorial Pacific region during the second half of 2005, which became colder during the beginning of 2006. However, since February 2006, equatorial Pacific region has warmed up again to return to near neutral conditions. A majority of the statistical and coupled model forecasts indicate higher probability (around 65%) for near neutral conditions to continue over the equatorial Pacific during the monsoon season.

By the first week of July, IMD will issue an update forecast for the monsoon rainfall over India along with the forecast for the July rainfall over the country as a whole and seasonal (June-September) rainfall over the four broad homogeneous regions of India. On 24th April 2006, the India Meteorological Department (IMD) issued the long range forecast for the 2006 south-west monsoon season rainfall as 93% of the Long Period Average (LPA) with a model error of ±5%. Now, IMD has prepared the forecast for monsoon onset over Kerala.

ON 24TH April, 2006, the India Meteorological Department (IMD) issued the long range forecast for the 2006 south-west monsoon season rainfall as 93% of the Long Period Average (LPA) with a model error of ±5%.

Source : Press Information Bureau
Date : May 15, 2006