Source : INDIA TODAY NEWS
Chennai’s main weather station collected 69.5 mm of rain in the 24 hours to 8.30 am on Saturday, October 17. That is about 70 litres of water on every square metre of ground.
The downpour came just two days after the northeast monsoon began. The India Meteorological Department (IMD) said monsoon rains commenced over Tamil Nadu, Puducherry and Karaikal on October 15, the same day the southwest monsoon, which brings rain from June to September, withdrew from the entire country. The airport recorded 37.2 mm in the same period, and Perambur in north Chennai got 9 cm, the highest in the city. A millimetre of rain means one litre of water on every square metre, so 9 cm is 90 litres.
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THE SEASON THAT BELONGS TO TAMIL NADU
The northeast monsoon is the main rainy season for Tamil Nadu and the coast around Chennai.
For Chennai, this season, not the June to September monsoon, brings most of the year’s rain. In October, the winds over southern India turn. They blow from the north-east, pick-up moisture over the Bay of Bengal and drop it on the east coast. IMD said easterly and north-easterly winds have now set in over the southern peninsula and the neighbouring Bay of Bengal.
TWO FEATURES HIGH IN THE SKY
This spell did not come from a cyclone, but from two features in the upper atmosphere that turned ordinary showers into a heavy one.
The first is an upper-air cyclonic circulation, a swirl of winds high above the ground that tends to push air upwards and build thick rain clouds. IMD said it moved over north Tamil Nadu and neighbouring south coastal Andhra Pradesh, between 4.5 and 5.8 km above the ground.
The second is a trough, a long, stretched-out zone of low pressure along which air gathers and rises. This one linked a circulation over northern Lakshadweep to the south-west Bay of Bengal, running across Kerala and Tamil Nadu.
IMD’s bulletins did not report a low-pressure area over the Bay of Bengal, and no system has been named.
WHERE ELSE IT RAINED
Chennai was not the wettest place in the state.
In the same 24 hours, Uthiramerur in Kancheepuram district recorded 148 mm, or 15 cm, the highest in Tamil Nadu. Puducherry recorded 96 mm. IMD describes the northeast monsoon as active over Tamil Nadu.
WHAT COMES NEXT
The rain has not finished.
IMD’s Chennai centre had forecast moderate to heavy rain at times in the city on October 17 and 18. For the wider region, it expects fairly widespread to widespread rain over Tamil Nadu, Puducherry, and Karaikal until October 22, with isolated very heavy rain until October 20. Isolated thunderstorms are likely, with gusty winds of 40 to 50 kmph.
The department has warned of waterlogging, localised flooding and disruption to road and rail traffic. Farmers have been advised to drain excess water from paddy nurseries and fields, and to harvest mature rice and groundnut in rain-free spells.
– Ends
SOURCE :- TIMES OF INDIA
