Met office said under the influence of yesterdayâs upper air cyclonic circulation over Northwest Bay of Bengal and adjoining North Odisha coast, a Low Pressure area has formed over Northwest Bay of Bengal and adjoining North Odisha-West Bengal coasts.
The associated cyclonic circulation extends upto 7.6 km above mean sea level tilting southwestwards with height. Itâs likely to become more marked during next 2-3 days.
Yesterdayâs off-shore trough at mean sea level runs from South Gujarat to Karnataka persists.
On the forecast for Tamil Nadu and Puducherry for the next seven days, it said  heavy rain is likely to occur at isolated places with thunderstorm and lightning, accompanied by gusty winds with speed reaching 30-40 kmph over Nilgiris, Theni district and Ghat areas of Coimbatore district tomorrow. Moderate rain at isolated places with thunderstorm and lightning with gusty winds speed reaching 30-40 kmph at one or two places is also likely to occur over rest Western Ghat districts and North Tamil Nadu districts like Chennai and adjoining districts.
Light rain at isolated places with thunderstorm and lightning at one or two places is likely to occur over rest of Tamil Nadu, Puducherry and Karaikal area.
On July 4, heavy rain is likely to occur at isolated places with thunderstorm and lightning with gusty winds speed reaching 30-40 kmph over Nilgiris, Coimbatore and Kanyakumari districts. Light to moderate rain at isolated places with thunderstorm and lightning with gusty winds speed reaching 30-40 kmph at one or two places is likely to occur over rest Western Ghat districts of Tamilnadu.
It said moderate rain at isolated places is likely to occur over Western Ghat districts of Tamilnadu on July five and six, while .
light to moderate rain at isolated places is likely to occur over Western Ghat districts and Delta districts of Tamil Nadu the next day and light to moderate rain at isolated places is likely to occur over Western Ghat districts of Tamil Nadu with light rain at isolated places over rest of Tamil Nadu, Puducherry and Karaikal area on July eight.
There would be no large change in maximum temperatures during day over Tamil Nadu, Puducherry and Karaikal area for the next 4-5 days.
The forecast for Chennai city and its neighbourhood is sky conditions would be partly cloudy with light to moderate rain with thunderstorm and lightning likely to occur during evening/night hours for the next two days.