A cyclonic circulation lying over the central parts of the Bay of Bengal and an incoming easterly wave will combine to trigger isolated to scattered light or moderate rainfall over gateway Andaman and Nicobar Islands, Karnataka, Kerala, Tamil Nadu and Lakshadweep during the next 4-5 days spilling over into the first few days of December.

This will be a prelude to what global models see an expansive phase of rainfall signalling the end of the ongoing lull phase in the North-East monsoon as another cyclonic circulation emerges over the South-East Bay of Bengal around December 4 and goes on to acquire strength as it moves towards coast.

Isolated heavy rain

Meanwhile, India Meteorological Department (IMD) said rain or thundershowers occurred at many places over Kerala and Mahe and at a few places over the Andaman and Nicobar Islands, Coastal Karnataka, Tamil Nadu, Puducherry and Karaikal through Monday and until 8.30 am on Tuesday. 

Thundershowers also lashed isolated places over Coastal Karnataka, Konkan, Goa, Madhya Maharashtra, Nagaland, Manipur, Mizoram and Tripura as an non-typically lean phase prevailed over the South Peninsula during what would otherwise be a peak North-East monsoon.

 Lull prevails over South

The lull had set in after a well-marked low-pressure area toyed with the North Tamil Nadu and South Andhra Pradesh coast for an unusually extended period, and chose to dump most of the rainfall over the seas even as cool air from North-West India flew into the vacuum over land. 

This had caused evening and night temperatures to dip to levels not seen in the recent past. The trend was reversed after the laggard weather system managed to cross the coast, bring warm and moist air to raise night temperatures to their normal, and drop rain mostly along the coast while the interior managed to make some spillover gains. 

Isolated very heavy rain

But the Bay had lost precious kinetic energy to the ill-behaving well-marked low-pressure area. The circulation now active over the central parts has managed to send north-easterly winds along the coast into the southern parts of Tamil Nadu and adjoining Kerala. A trough too has formed off the coast Kerala waiting to receive these north-easterly winds and their moisture content.

The main centres receiving moderate to heavy rain (in cm) in this manner on Monday are Kannimar-12; Mambzhathuraiyaru and Anaikedanku-9 each; Bhoothapandy-8; Thuckalay, Sothuparai and Manjalar-7 each in Tamil Nadu and Konni and Punalur-11 each; Piravom and Koothattukulam-9 each; Enadimangalam and Thodupuzha-7 each in Kerala. 

An extended three-day outlook from the IMD said the fresh cyclonic circulation emerging over the South Andaman Sea around December 4 (Sunday next) will bring fairly widespread to widespread rainfall with isolated heavy falls over the Andaman and Nicobar Islands. Scattered to fairly widespread light/moderate rainfall activity is indicated for the South Peninsula during this period.