The India Meteorological Department (IMD) announced on Friday that the southwest monsoon is likely to arrive in Kerala on May 26, marking an early start to the rainy season. Typically, the monsoon sets in over Kerala around June 1, with a standard deviation of seven days. This year, the IMD's operational forecast predicts the onset with a model error of ±4 days.
Accuracy of IMD Forecasts
According to the met department, its operational forecasts for the date of monsoon onset over Kerala have been accurate for the past 21 years (2005-2025), with the exception of 2015. It is important to note that an early or late arrival does not necessarily indicate the overall performance or distribution of the monsoon. Last year, the monsoon arrived over Kerala eight days ahead of schedule, on May 24.
Below Normal Rainfall Predicted
The IMD has already forecast 'below normal' monsoon rainfall this year across many parts of the country, citing the growing risk of El Nino. El Nino conditions are invariably associated with harsher summers and weaker monsoons in South Asia. Meanwhile, on Friday, the IMD stated that conditions are favorable for the advance of the southwest monsoon over parts of the south Bay of Bengal, the Andaman Sea, and the Andaman & Nicobar Islands within the next 24 hours.
Significance of Monsoon Onset
The onset of the monsoon in Kerala marks the arrival of the southwest monsoon on the Indian mainland. This event is a crucial indicator, characterizing the transition from hot and dry conditions to the rainy season.
Forecast Methodology
The IMD has been issuing operational forecasts for the date of monsoon onset over Kerala since 2005, using an indigenously developed statistical model with a model error of ±4 days. The model incorporates six key predictors:
- Minimum temperatures over northwest India
- Pre-monsoon rainfall peak over the south Peninsula
- Outgoing longwave radiation (OLR) over the South China Sea
- Lower tropospheric zonal wind over the equatorial southeast Indian Ocean
- Outgoing longwave radiation (OLR) over the southwest Pacific Ocean
- Lower tropospheric zonal wind over the equatorial northeast Indian Ocean
These predictors help the IMD make accurate onset forecasts, which are vital for agricultural planning and water resource management across the country.
