As per the latest update by the India Meteorological Department (IMD), the 2023 monsoon onset over Kerala will be on June 4, with a model error of ± 4 days.

Over the last 50 years, the date of onset in Kerala has ranged from May 19 (in 1990) to June 18 (in 1972). This variance is largely attributed to the state of the El Niño-Southern Oscillation (ENSO) in the preceding winter, with the Madden-Julian Oscillation (MJO) — a tropical wave that travels around the equator every 30-40 days — also playing a role.

In fact, the IMD has been issuing such operational forecasts for the monsoon onset date over Kerala since 2005. During this period, the predicted onset dates were proven correct for 17 of the 18 years between 2005-2022, with the only exception being 2015.

IMD’s indigenously-developed, state-of-the-art statistical model uses six predictors to issue onset date forecasts, which include:

1. Minimum Temperatures over Northwest India
2. Pre-monsoon rainfall peak over South Peninsula
3. Outgoing Long-wave Radiation (OLR) over South China Sea
4. Lower tropospheric zonal wind over Southeast Indian Ocean
5. Mean sea level pressure over Subtropical NW Pacific Ocean
6. Upper tropospheric zonal wind over North East Indian Ocean

Meanwhile, the IMD’s long-range forecast has indicated that the monsoon’s performance this year is likely to be normal. Quantitatively, the seasonal precipitation may amount to 83.5 cm — around 96% of India’s long-period average for monsoons.

O​n the other hand, The Weather Channel’s forecast for monsoon 2023 paints a slightly drier picture. It has predicted seasonal rainfall worth 80.4 cm, which is about 92% of India’s LPA.

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