Two weather systems likely to trigger heavy rain over south T.N.

Two weather systems, with the prospects of intensifying, are expected to trigger heavy rainfall, particularly over south Tamil Nadu districts, pushing Northeast monsoon into a more vigorous phase this week. Some northern districts, including Chennai, may see intense rain on November 29 and 30.

The Regional Meteorological Centre (RMC), Chennai, is monitoring the weather systems’ development and trajectory to assess changes in rainfall impact. According to it, a well marked low-pressure area now lies over Malaysia and the adjoining Strait of Malacca along with an associated cyclonic circulation. It is expected to concentrate into a depression over the South Andaman Sea by Tuesday and intensify into a cyclonic storm over the South Bay of Bengal by Thursday. If the system gains strength as cyclonic storm, it may be named ‘Senyaar’, a name given by the United Arab Emirates.

Currently, the upper air circulation over Comorin area and neighbourhood, which is likely to develop into a low-pressure area by Tuesday and intensify further, is influencing rainfall in the State. Torrential downpour for the past two days has wiped out the seasonal rain deficit in the State, pushing the figures to surplus by 5% on Monday. Tamil Nadu has received 34 cm of rainfall against its normal of 32.3 cm since October 1. A few districts, including Chennai, Chengalpattu, and Dindigul, still have a rain shortfall.

Downpours across State

During the past 24 hours ending 8.30 a.m. on Monday, many places received heavy rainfall, with Oothu in Tirunelveli district topping the list with 23 cm. While wet weather over the State will persist till the month-end, the RMC has forecast heavy rainfall to continue over four districts, including Tirunelveli and Ramanathapuram, on Tuesday. Intense downpour may cover more places in south and delta districts as the weather systems develop. The department has issued orange and yellow alerts for various districts between November 28 and 30.

It may be the turn of northern districts, including Chennai and Chengalpattu, to receive very heavy rain on November 29. An orange alert has been issued to Tiruvallur district for November 30.

B. Amudha, Head, (Additional in-charge), RMC, said the interaction between the three weather systems, including another cyclonic circulation over southeast Arabian sea, would influence changes in the weather dynamics and rainfall potential. Such interaction of systems, particularly in the equatorial trough zone, were likely during the Northeast monsoon, with one feeding the other with moisture.

“We are monitoring the possibility of the system near the Strait of Malacca merging with the one near the Comorin area and moving as a single weather system. There will be more clarity in two or three days about the weather disturbances,” she said.

On the torrential downpour in southern districts, Ms. Amudha said localised activity in some places along the ghat areas could sometimes enhance the rainfall intensity. “We are expecting November rainfall to be normal as rain associated with weather systems may spike the seasonal numbers and erase the deficit,” she added.