Vinson Kurian

Thiruvananthapuram, Dec. 5

SUNDAY'S `low' over south Andaman Sea has crossed into the Bay of Bengal overnight and lay some 650 nautical miles (1,200 km) east-southeast of Chennai at 3 p.m. on Monday.

The location was traced to almost the same latitude as Jaffna in eastern Sri Lanka but the circulation had well-developed features that bested even predecessor Tropical Cyclone Baaz at a comparable stage, said Dr K.J. Ramesh of the National Centre for Medium Range Weather Forecasting (NCMRWF).

The Joint Typhoon Warning Centre (JTWC) has measured the maximum sustained wind speed buffeting the system at about 30-35 km/h. It is expected to move west-northwest, the beaten track for most storms taking shape over the Bay waters during this time of the year.

Under its influence, coastal Tamil Nadu and south coastal Andhra Pradesh are likely to receive a fresh spell of fairly widespread to widespread rains with isolated heavy falls from Wednesday/Thursday, the NCMRWF said in its forecast on Monday. The fertile shear zone of turbulence extending from east to west will likely help the system graduate soon enough to become a well-marked low, the next scale in terms of intensity.

Weakened westerlies: Importantly, the circulation will not be made to encounter the westerlies that blew away `Baaz' as it approached land. This giant-killer westerly trough has lately been reduced to insignificance, Dr Ramesh said. Upper level analysis carried out by the University of Wisconsin-Madison (UWM) indicated that the Bay circulation remained in a region of low to moderate vertical wind shear only.

Microwave imagery depicted a larger and more symmetric circulation than what was observed earlier, the UWM said. Due to an increase in convection, the potential for the development of a significant tropical cyclone within the next 24 hours is upgraded to fair, its forecast said.

According to Dr Ramesh, what could possibly inhibit the system from intensifying beyond a point is the prevailing cooler anomaly in the coastal waters of eastern peninsula left behind by Baaz's passage. If the as yet unnumbered/unnamed system were to curl in fast and not allow the breather for southwest Bay to warm, it could slow down, if not entirely change course. Meteorologists are closely watching the system as it progresses.

In its weather update, the NCMRWF said that scattered to fairly widespread rainfall was reported from north Tamil Nadu, Lakshadweep, Kerala, Karnataka and the Andaman and Nicobar Islands during the 24 hours ending Monday morning. The remnant upper air cyclonic circulation from `Baaz' had moved out from Sunday's perch over the Malabar Coast into southeast Arabian Sea.

The east-west shear zone continued to feature three cyclonic circulations, two of them over the Arabian Sea and the other one over the Bay of Bengal. Moderate rainfall activity is expected to continue over south peninsular India in view of this active shear zone.

In its forecast for the next four-five days, the NCMRWF said isolated to scattered rains are expected over south India for the next two days due to the moderate convective activity in the zone. The new cyclonic circulation system over southeast Bay is expected to trigger a fresh spell of rain over coastal Tamil Nadu and Andhra Pradesh likely from Wednesday. Subsequently, fairly widespread to widespread rains with isolated heavy falls are expected to lash north Tamil Nadu and south coastal Andhra Pradesh.

(This article was published in the Business Line print edition dated December 6, 2005)
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