A new depression has formed over the Arabian Sea and is expected to intensify over the next 24 hours, according to the weather centre. The system is likely to strengthen the northeast monsoon across several parts of Tamil Nadu.
For Chennai, the weather centre has issued a red alert for extremely heavy rainfall on October 18. Rainfall of more than 20 cm is possible.
Residents have been advised to avoid stepping out unless necessary and to stay in safe locations. Civic agencies and rescue teams have also been instructed to remain on standby.
An orange alert for very heavy rain has been issued for five districts on October 18: Chengalpattu, Tiruvallur, Nilgiris, Coimbatore and Theni.
A yellow alert for heavy rain has been issued for 23 districts: Kanyakumari, Tirunelveli, Tenkasi, Thoothukudi, Virudhunagar, Madurai, Sivaganga, Ramanathapuram, Dindigul, Pudukkottai, Thanjavur, Tirupathur, Tiruppur, Nagapattinam, Mayiladuthurai, Cuddalore, Kallakurichi, Villupuram, Tiruvannamalai, Vellore, Ranipet and Kanchipuram.
