However, weather experts are still not sure how strong the cyclone would be or where it would make the landfall on November 25.

What is almost certain is, whether it is strong or weak or makes a landfall on the north or south of Karaikal, Chennai, its neighbourhood and most parts of north Tamil Nadu are in for an extremely heavy spell of rain. But the rain activity in southern parts of the State and interiors remains unclear.

“The cyclonic depression has intensified into a barometric depression. As it is still a depression and not yet a cyclone, the path is a little unpredictable due to the factors of the upper air trough and anti-cyclone phenomena, which could change the course. However, it is likely to cross between Mahabalipuram and Karaikal on November 25 afternoon,” said N Puviarasan, Director, Area Cyclone Warning Centre of the Regional Meteorological Centre, Chennai.

By Monday evening, it became a deep depression located about 480 km southeast from Chennai and moving in a northwesterly direction. “Coastal districts can expect wind speeds between 80 and 90 kmph on Tuesday. When the storm crosses the coast on November 25, the speed could reach 100 to 110 kmph,” he added.

According to popular weather blogger Pradeep John, Cyclone Nivar, which once had simple steering, has become complex, leading to two possible scenarios:

In the first one, landfall will be between Vedaranayam to Karaikkal as a weaker cyclone. Likely windspeeds are expected to between 70 kmph, with extreme rainfall in Tiruvarur, Nagai, Thanjavur, Perambalur, Ariyalur and Karaikal, and very heavy rainfall in Chennai, Tiruvallur, Kancheepuram, Chengalpattu, Tiruvarur, Tiruchy, Namakkal, Salem, Villupuram, Tiruvannamalai, Kallakuruchi, Vellore, Cuddalore, Puducherry and Ranipet.

In the second scenario, which is more likely in John’s opinion, the possible landfall will be between Chennai and Karaikal, and a strong cyclone with wind speeds between 120 kmph to 140 kmph. In this case, there will be extreme rainfall in Chennai, Kancheepuram, Chengalpattu, Cuddalore, Puducherry, Villupuram, Vellore, Tiruvannamalai and Ranipet, and very heavy rainfall in Kallakuruchi, Nagapattinam, Karaikal, Perambalur and Ariyalur.

“Heavy rains are confirmed for entire north TN including north interiors but still crossing point remains a probability. One more point to be noted is that in recent years, all cyclones have ended 20-30 kmph on higher side than what was predicted by models,” added Pradeep John.