Thiruvananthapuram: Kerala is likely to receive heavy to very heavy rainfall over the coming days as the northeast monsoon is set to commence over the southern peninsula on Thursday, the India Meteorological Department (IMD) said on Wednesday.

The weather department has issued an orange alert in Pathanamthitta, Kottayam, Ernakulam and Idukki districts for October 15, warning of very heavy rainfall. A yellow alert has been issued in eight other districts for the day. An orange alert indicates very heavy rainfall of 12 cm to 20 cm in 24 hours, while a yellow alert indicates heavy rainfall of 7 cm to 11 cm.

The IMD said conditions were becoming favourable for the withdrawal of the southwest monsoon from the remaining parts of the country and the simultaneous onset of northeast monsoon rains over the southern peninsula on October 15.

According to the forecast, isolated places in Kerala are likely to receive heavy to very heavy rainfall of 7 cm to 20 cm on Thursday. Heavy rainfall is also likely at isolated places from October 16 to 20. The IMD has also forecast thunderstorms accompanied by lightning and gusty winds in the state over the coming days.

On October 15 and 16, thunderstorms accompanied by lightning and winds reaching 40-50 kmph are likely at one or two places. Similar conditions, with wind speeds of 30-40 kmph, are expected at isolated places on October 14, 17 and 18.

The weather department attributed the conditions to an upper-air cyclonic circulation over central parts of Kerala and adjoining areas at an altitude of 4.5 km above mean sea level, along with another circulation over the Comorin region and neighbourhood.

Thunderstorms accompanied by lightning are also likely at one or two places in Lakshadweep from October 14 to 16.