Kerala gears up to receive northeast monsoon

State is likely to receive widespread light to moderate rainfall for five days

The northeast monsoon, also known as Thulavarsham, is likely to set in over Kerala by Thursday, simultaneously completing the withdrawal of the southwest monsoon from the country.

With the setting in of easterly and northeasterly winds over southern peninsular India and south and adjoining central Bay of Bengal, the northeast monsoon rainfall activity is likely to commence over the south-east peninsular region in the next four days, according to India Meteorological Department (IMD) on Sunday.

For the pluviophiles, the northeast monsoon is not an uninterrupted rain like in the southwest monsoon period. On the contrary, Thulavarsham brings rain in spells, often heavy spells accompanied by lightening and thunderstorms, along with a strong surge of cold air from the anti-cyclone located over Siberia and the adjoining parts of China. For Kerala, it brings roughly 500 mm of rain during the period from October middle to December.

The average onset date of northeast monsoon for the period 1901-2021 is on October 19 with a standard deviation of plus or minus 8 days. Hence, the Thulavarsham can be expected in Kerala on any date from October 11 to 27, which is the normal onset date of post-monsoon in south India. The highest number of onsets took place on October 15 (11 times), followed by October 19 (9 times). The most delayed onset was on November 11 in 1915, and the earliest onset was on October 4 (1952,1966,1984 and 1999).

Many features that were part of the onset phase of the southwest monsoon will now start to weaken, like the disappearance of the easterly jet that dominates the southwest monsoon, and the reappearance of subtropical westerly jet stream over the northwestern end of the Himalaya with the beginning of the Asian winter monsoon, which also generates rain in countries such as Sri Lanka, Malaysia, and Indonesia apart from south India. Setting the tone for the Thulavarsham, a twin weather system is brewing in the Arabian Sea and the Bay of Bengal.

Depression

The well marked low-pressure area over eastcentral Arabian Sea is likely to intensify into a depression over central Arabian Sea during the next 12 hours, according to IMD on Sunday. In addition, a low pressure area is expected to take shape over central parts of the south Bay of Bengal around Monday. It is likely to become well marked low pressure area and move west-northwestwards towards north Tamil Nadu, Puducherry and adjoining south Andhra Pradesh coasts during the subsequent 48 hours. Under the influence of the twin system and associated features, the State is likely to receive widespread light to moderate rainfalls for five days. Above normal season is also predicted for Kerala by the IMD this year.

Published - October 14, 2024 12:09 am IST