IMD will issue the updated monsoon forecast by the first week of June 2016 based on the operational model and with the updated data upto May 2016.
Climatologically monsoon is expected to reach South Kerala by 31st May. The forecast for the 2016 monsoon onset date will be issued on 15th May, 2016.
Monsoon onset over Kerala follows the monsoon advancement over the Andaman Sea that climatologically falls around 20th May. So as to account for the Monsoon advancement over Andaman Sea, the monsoon onset forecast over Kerala is issued around middle of May annually.
Although, Potsdam Institute for Climate Impact Research, Germany has claimed a novel method to forecast monsoon onset over the Eastern Ghats (North Coastal Andhra Pradesh and adjoining Southern Odisha) and monsoon withdrawal from North Pakistan only, the methodology adopted has some limitations and uncertainty. At the same time, the respective withdrawal predictions have shown reduced skill during recent 2010-2014 period. As the methodology has not been tested for monsoon onset over the South Kerala, no tangible gain is expected for our operational onset monsoon forecast.
However, IMD issues the monsoon onset forecast based on an indigenously developed model. The forecasts for monsoon onset for last 10 years have been found correct.
The monsoon forecast during last three years was as under;
| Year | Forecast | Actual (% of LPA) | |
| Issued in April | Issued in June | ||
| 2013 | 98 % of LPA ± 5 | 98 % of LPA ± 4 | 106 |
| 2014 | 95 % of LPA ± 5 | 93 % of LPA ± 4 | 88 |
| 2015 | 93% of LPA with a model error of ± 5% | 88% of LPA ±4% | 86 |
The forecast for monsoon during 2014 & 2015 were correct. However during 2013, the monsoon forecast issued by India Meteorological Department (IMD) was marginally under estimated. It may be mentioned here that both 2014 & 2015 were deficient monsoon years.
