Exit of southwest monsoon, onset of northeast monsoon likely to be on October 16

The exit of the southwest monsoon and the onset of the northeast monsoon are expected to happen simultaneously this year. According to the weather bulletin issued by the India Meteorological Department (IMD), conditions are favourable for the full exit of the southwest monsoon, the process that began from Rajasthan on September 14, three days ahead of the normal withdrawal. It is expected to be completed by October 16.

Simultaneously, the setting in of easterly and northeasterly winds over southern peninsular India and south and adjoining central Bay of Bengal will mark the onset of the northeast monsoon across the State. The previous simultaneous exit and onset was in 2019. The criteria required for the declaration of the onset, such as the southwest monsoon withdrawing up to coastal Andhra Pradesh, have almost been met.

Also, Easterlies (up to 850 hPa) should set in over Tamil Nadu or seasonal low should be established in South Bay of Bengal adjacent to Tamil Nadu coast. An upper air cyclonic circulation lies over south coastal Tamil Nadu and adjoining Comorin area extending up to 1.5 km above mean sea level. Another upper air cyclonic circulation lay over southeast Arabian Sea and adjoining Lakshadweep area. Under its influence, a low-pressure area is likely to form over southeast Arabian Sea and Lakshadweep area off Kerala-Karnataka coasts around October 19.

Extreme events unlikely

All these conditions are favourable for the commencement of the northeast monsoon (also called winter monsoon and Thulavarsham in local parlance) with a vigorous spell. Though the weather system is expected to trigger some intense spells of rain across the State, especially in southern Kerala and parts of central Kerala, the chance for extreme weather events is unlikely. However, the ghat areas are likely to witness some intense spells.

An orange alert has been issued for Idukki and Kottayam on Thursday, where very heavy rainfall is likely, while seven districts, including Thiruvananthapuram, Kollam, Pathanamthitta, Alappuzha, Ernakulam, Thrissur, and Malappuram, have been put on yellow alert warning of heavy rainfall.

Highest rainfall

Meanwhile, Kanjirappally in Kottayam recorded the highest rainfall of 18 cm during the last 24 hours ending at 8.30 a.m. on Wednesday, followed by Neryamangalam in Ernakulam (10 cm), and Kunnathanam in Pathanamthitta (7 cm). Although the westerlies are still prevailing over the State, the rain is considered as a precursor to the northeast monsoon.