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After an agonising wait for more than a day in the waters off the South Andhra Pradesh and North Tamil Nadu coasts, Monday’s depression weakened into a well-marked low-pressure area over West-Central and adjoining South-West Bay of Bengal by 8.30 am on Tuesday morning, the India Meteorological Department (IMD) has confirmed.
The system was located tantalisingly close to the coast in the morning and towards noon, and had even conjured up a rare night when temperatures cooled to levels rarely seen before. It was even trending on Twitter with hashtag #ChennaiSnow through Monday evening, with several memes.
Temperatures hit lows
Twitter handles went wild, giving a hilarious touch to the night of cold weather in the southern metropolis - to the extent of drawing a parallel with ‘North Pole-like situation,’ as one of them put it. Yet others let their imaginations run riot, featuring how their counterparts in the North, who are used to winter and snow, would react to ‘ChennaiSnow’ trending on the internet. All this was triggered when the mercury hit a low of 22.5°C on Monday evening, the cold amplified by a steady breeze, even as the depression lowered anchor for much longer than expected. It later yielded way to dense, cooler winds from the North-West, at the lower levels of the atmosphere, bringing down the ambient temperature at the ground level.
High wind shear
The warm and moist air from the sea dragged in by the depression, marked by lower pressure, was driven up to the higher levels. Not much had changed the morning after, with the depression staying put, except that it has weakened a round to a well-marked ‘low.’ The noon update by the IMD on Tuesday said the system will move towards the coast and weaken further by Wednesday. Global models said its proximity to the coast meant the system braved opposing dry and cool winds (leading to shearing of clouds) emanating from the North-West of the country, which is transitioning slowly from autumn to winter. Also, sea-surface temperatures were relatively cooler than the outer seas, where the depression had sustained overnight.
Easterly wave seen
The IMD has called attention to another cyclonic circulation likely emerging over the North Andaman Sea by Thursday. But it is forecast to lose its way midway and get scooped up northwards towards the Myanmar coast, apparently under the influence of another passing western disturbance. It may throw down a trough reaching the West-Central Bay of Bengal. Easterly winds directed towards Sri Lanka and Tamil Nadu are forecast to strengthen subsequently from an ‘easterly wave’.
The IMD had earlier said in an extended outlook that the easterly wave and cyclonic circulation will combine to set off scattered to fairly widespread rainfall activity over many parts of the South Peninsula during the first half of the week starting Thursday. Overall rainfall is likely to be normal to above normal over here, and below normal over the rest of the country during the week.
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