Date:28/10/2009 URL: http://www.thehindubusinessline.com/2009/10/28/stories/2009102850871901.htm

Back Stage set for onset of north-east monsoon

Vinson Kurian

Thiruvananthapuram, Oct. 27

Conditions are favourable for the commencement of the northeast monsoon over Tamil Nadu and the adjoining meteorological subdivisions during the next two days.

An India Meteorological Department (IMD) update said on Tuesday that the eastto- west trough from southeast Arabian Sea to south Andaman Sea through south Bay of Bengal levels persisted from overnight.

EMBEDDED CIRCULATION

The trough featured an embedded cyclonic circulation over southeast Arabian Sea. The previous day's cyclonic circulation over the southeast Bay of Bengal ceased to exist as easterlies from the South China Sea swept into the Bay.

Thus, the prevailing winds over the Bay of Bengal had turned easterly from being northeasterly heralding conditions considered favourable for the onset of the northeast monsoon.

IMD also assessed that the mainly easterly (towards the south) and partly northeasterly winds over the Bay basin and south peninsular India would strengthen further on Wednesday.

Scattered to fairly widespread rainfall activity is likely over extreme south peninsular India during the next three to four days, the IMD added.

The Regional Met Centre, Chennai, too said in its update that conditions were favourable for the onset of seasonal rains over Tamil Nadu, Puducherry, and adjoining areas of Kerala, Karnataka and Andhra Pradesh during the next two to three days.

During the 24 hours ending Tuesday morning, rainfall occurred at a few places over Kerala. Isolated rainfall occurred over Tamil Nadu, coastal Andhra Pradesh and Rayalaseema.

HEAVY RAINS

Mavelikara and Kayamkulam (both Alapuzha district) recorded very heavy and heavy rainfall of 13 cm and 7 cm respectively. Forecast until Thursday said that rain or thundershowers were likely at a few places over coastal Tamil Nadu, Puducherry, Kerala, Rayalaseema and south coastal Andhra Pradesh.

Isolated rain or thundershowers have been forecast for interior Tamil Nadu, north coastal Andhra Pradesh, coastal Karnataka, south interior Karnataka and Lakshadweep.

Satellite imagery on Tuesday showed the presence of convective clouds over parts of south Andaman Sea and southwest Bay of Bengal.

Meanwhile, the European Centre for Medium-Range Weather Forecasts (ECMWF) said that relative humidity had been pumped up to between 80 to 95 per cent over south coastal Tamil Nadu and the Kerala coast as early as from Monday.

But the rainfall generated overnight has not been widespread with isolated very heavy to heavy rains being confined mostly over Kerala and less so over Tamil Nadu.

These high humidity levels will be retained mostly through Wednesday as well, though ECMWF forecasts saw the build-up going up to even 100 per cent over parts of north interior Tamil Nadu translating into assured rains.

Moisture transport

By Thursday, increased moisture transport and strengthening wind speeds would help beef up humidity to 100 per cent and trigger widespread rains all over coastal Tamil Nadu and Puducherry.

The rest of the southern peninsula too will share the spoils at humidity levels of up to 95 per cent, the ECMWF said.

First available indications of an approaching winter were palpable over north India with minimum temperatures climbing down variously at many places overnight.

Minimum temperatures were below normal by 3 to 6 degree Celsius over Haryana, Uttar Pradesh, Bihar, Orissa, Chhattisgarh, west Madhya Pradesh, Telangana and parts of Maharashtra.

Causative northwesterly/northerly winds are prevailing over these regions in the lower levels, the IMD said. A western disturbance as a westerly trough is likely to affect the western Himalayan region during the next two-three 2-3 days.

The arrival phase of the disturbance may cause the air to warm up with the rising motion up front. But the passage of the western disturbance will allow colder northwesterlies to penetrate the northwest region.

Isolated rain or snow has been forecast over the western Himalayan region during the next two-three 2-3 days. Minimum temperatures are likely to increase by 2-3 degree Celsius over parts of northwest (thanks to the arrival phase of the western disturbance) and peninsular India.