Cyclone warning signals have been hoisted at nine ports, including Nagapattinam, Chennai, Cuddalore, Karaikal, Pamban and Thoothukudi. Chennai, Oct 24 (PTI) The IMD on Saturday warned of heavy to very heavy rain over the Nilgiris district and forecast heavy rainfall activity in several districts of Tamil Nadu for the next three days. IMD issues a red alert for extremely heavy rainfall and thunderstorms across Kerala, Tamil Nadu, Puducherry, and other southern states.