Monsoon to arrive early over Kerala

IMD says it will make its onset on May 27, four days ahead of the normal date of June 1 

Monsoon is slated to make its earliest arrival in 13 years over Kerala. The India Meteorological Department (IMD) said on Friday that the monsoon will make its onset over the State on May 27, four days ahead of its normal date of June 1.

IMD records show that the monsoon arrived on May 23 in 2009, May 26 in 2006 and May 28 in 2007. The last time the monsoon arrived in Kerala in May was 2018.

The IMD uses a specialised model that forecasts the arrival dates within a four-day window. It uses six predictors — Minimum Temperatures over North-west India, pre-monsoon rainfall peak over south Peninsula, Outgoing Long wave Radiation (OLR) over South China Sea, lower tropospheric zonal wind over southeast Indian Ocean, upper tropospheric zonal wind over the east equatorial Indian Ocean, and Outgoing Long wave Radiation (OLR) over the south-west Pacific region.

Except for 2015, monsoon has arrived within the four-day window of the date forecast by the IMD from 2005 to 2021, the IMD said in a press statement.

The monsoon’s arrival over India is marked by monsoonal rains over south Andaman Sea which then advance north-westwards across the Bay of Bengal. Usually, the southwest monsoon advances over the Andaman Sea around May 22. But this year, said D.S. Pai, a senior forecaster with the IMD, monsoon has nearly reached the Andamans.

In association with enhanced cross equatorial winds, conditions are becoming favourable for southwest monsoon advancing into South Andaman Sea, Nicobar Islands and some parts of southeast Bay of Bengal, around May 15, the IMD statement noted.

However, there is little correlation between the monsoon’s arrival and the quantum of rainfall. In 2009, for instance, the monsoon’s early arrival failed to inure India against its biggest drought in 40 years. “Past data suggest that there is no association of the date of monsoon advance over the Andaman Sea either with the date of monsoon onset over Kerala or with the seasonal monsoon rainfall over the country,” according to the IMD.