CHENNAI: Less than a week after very severe cyclonic storm Nivar made landfall near Marakkanam dumping vast amounts of rain, another weather system is on its way to the TN coast.
Weathermen said a low pressure area has formed over south Andaman Sea and is likely to move towards south Tamil Nadu after intensifying into a depression, bringing widespread rainfall from December 1. Extremely heavy rainfall can be expected in some parts of southern districts of TN, which have recorded a deficit so far since October 1, while northern districts, including Chennai, may receive heavy spells of rain. In its bulletin, IMD said the low pressure area has formed over south Andaman sea and adjoining areas of southeast Bay of Bengal and east equatorial Indian Ocean on Saturday. “It is very likely to move west-northwestwards and reach south Tamil Nadu coast on December 2,” the agency said.
Private weather forecasters said the system is likely to cross the Gulf of Mannar and Comorin Area before moving into the Arabian Sea. Weather bloggers said it may intensify into a weak cyclonic storm over the Arabian Sea far away from the Indian coast before moving towards Somalia or Oman.
IMD forecast “heavy to very heavy rainfall at a few places with isolated extremely heavy spells over south Tamil Nadu and south Kerala on December 2 and isolated heavy to very heavy rainfall over these regions on December 1 and 3. Over north Tamil Nadu, Puducherry, Mahe and Karaikal and north Kerala, heavy to very heavy rainfall at isolated places is likely from December 1 to 3”.
On November 30, Gulf of Mannar region could experience increased wind speeds of 45-55kmph gusting to 65 kmph and by December 1, it could 65-75kmph gusting to 85kmph along and off south TN coast and 50-60kmph gusting to 70kmph along and off north Tamil Nadu, Puducherry and Kerala coast, Comorin area and Gulf of Mannar. By December 2, wind speeds could further increase to 70-80kmph gusting to 90kmph along and off south Tamil Nadu and Kerala coasts, Comorin area and Gulf of Mannar. North Tamil Nadu and Puducherry coast as well as north Kerala coast could see winds at 55-65kmph gusting to 75kmph.
Weather blogger Pradeep John said Chennai will receive convective rainfall from wind convergence caused by the system pulling the easterlies into the land as it nears the Tamil Nadu coast and from the cloud bands around it. “South, southwest and delta regions, including Kanyakumari, Ramanathapuram and Tenkasi which have recorded a deficit so far this season, will receive very heavy spells. Hilly regions can expect good winds. This will be a rain-filled system,” he said.
Weather watchers said the system could, at the most, intensify into a deep depression when it is near the TN coast as it may not be over the sea for a longer period to gather moisture and strengthen into a storm. But global climate phenomenon like Madden-Julian Oscillation, an eastward moving disturbance of clouds, rainfall, winds and pressure, which is now in the Indian Ocean region and a warm sea surface temperature will add strength to the weather system.
Though there was an upwelling of the sea when cyclone Nivar crossed, Mahesh Palawat, chief meteorologist, Skymet Weather, said the sea surface temperatures are warmer at 28-29 deg C. “But this system will be fast moving and won’t spend much time over the sea to intensify. Any system requires to travel at least five to six days over the sea to gather moisture and strengthen into a cyclonic storm,” he said. Further, climate studies have shown that many weather systems that originated from the Andaman Sea had gone on to intensify into cyclonic storms.
Soon after this system nears Tamil Nadu, forecasters said another system may form over the same region of south Andaman Sea by December 8 or 9. So far, global weather models show that this system may intensify into another cyclonic storm, which is compact and strong, and is likely to move closer to Chennai or south Andhra Pradesh. “In December, systems usually form over the south Bay of Bengal and travel south, because north Bay of Bengal will be cooler, as the sun is in the southern hemisphere,” Palawat said.