Two weather systems are prevailing over the Bay of Bengal and the Arabian Sea.

Wet weather is on the cards for the next five days, with two weather systems prevailing over the Bay of Bengal and the Arabian Sea.

An upper air cyclonic circulation over the southwest Bay of Bengal and adjoining Sri Lanka is expected to bring moderate rainfall to most parts of Tamil Nadu and Puducherry till October 7. Chennai is likely to experience intermittent spells of light to moderate rain till Sunday.

What does India Meteorological Department's colour-coded weather warning mean? Colour-coded weather alerts are issued to State administrations to prepare for the impact of rainfall or weather events.

Green: No action

Yellow: Be updated (Heavy rains:7-12 cm)

Orange: Be prepared (Very heavy rains: 12.4-24.4 cm)

Red: Take action (Extremely heavy rains: above 24.4 cm)

On Oct 7, when a low pressure area over the southeast Arabian Sea is likely to intensify into a depression, districts like Chennai, Kancheepuram and Nagapattinam are expected to receive light rain

Districts like Tiruvallur, Villupuram, Perambalur, Namakkal and Dharmapuri may receive moderate to heavy rain

One or two places in districts like Tiruchi and Salem may receive heavy rainfall.

One or two places in districts in south Tamil Nadu and Western Ghats like the Nilgiris, Theni and Dindigul may experience extremely heavy rainfall.

A weather disturbance is likely to develop into a low pressure area over the southeast Arabian Sea on Friday and eventually intensify into a cyclone by October 7 and move towards the Oman coast.

‘Red’ alert issued

The India Meteorological Department has issued a ‘red’ alert.

S. Balachandran, Deputy Director General of Meteorology, Chennai, said heavy to very heavy rainfall was expected in the Western Ghats and south Tamil Nadu. There are chances of extremely heavy rainfall (above 24.4 cm) in one or two places in southern parts of the State and the Western Ghats region.

It was not an alert for the entire Tamil Nadu but a warning intended to get the government to take necessary action, he said.

While the Southwest monsoon was retreating, Wednesday’s rainfall came as precursor to the Northeast monsoon that may set in later this month. Most weather stations across the State received moderate rain on Thursday, with Kattumannarkoil in Cuddalore district and Pullambadi in Tiruchi district recording the highest of 11 cm in the 24 hours ending 8.30 a.m. on Thursday. Chennai received nearly 3 cm of rainfall.

On the rumours in social media about two cyclones forming simultaneously and heavy rain in Chennai, Mr. Balachandran said that as of now there was only a possibility of the weather system in the southeast Arabian Sea intensifying into a cyclone.

Weather bloggers have pointed to the possibility of another low pressure area over the southwest Bay of Bengal around October 8.