Wednesday, December 23, 2009

Easterly wave activates N-E monsoon

A prevailing easterly wave has helped power the NorthEast monsoon to be active over coastal Tamil Nadu during the 24 hours ending Tuesday morning.

Rainfall has been reported from many places over coastal Tamil Nadu and at a few places over interior Tamil Nadu. Isolated rainfall was reported over Kerala and Rayalaseema.

Wind Confluence

The confluence of winds traced over central India seems to have shifted to the seas. Opposing winds blowing into a trough had triggered activity over south-south-east Arabian Sea and adjoining southwest Indian Ocean.

In a similar fashion, a confluence has been taking place over southwest Bay of Bengal just to the east of Sri Lanka in association with the easterly wave.

Additional ground support was being provided by the sea-surface temperatures that continued to be elevated over south-east Arabian Sea and adjoining southwest Indian Ocean and slightly less so over the south-west Bay of Bengal.

Wind streamline maps over land showed that the easterlies blowing into the peninsula had pushed up the anti-cyclone to the north over the peninsula.

The north-easterlies filling the southern flanks of the anti-cyclone had caused the moisture-laden easterlies from the Bay of Bengal to make a token presence over the peninsula.

Rain forecast

The Regional Meteorological Centre, Chennai, has said in its forecasts for the next two days that rain or thundershowers are likely at many places over coastal Tamil Nadu.

Thundershowers are also likely at a few places over interior Tamil Nadu, Kerala and Lakshadweep. Isolated rain or thundershowers are likely over Rayalaseema and coastal Karnataka.

Cloud imagery on Tuesday showed convective clouds over parts of southwest Bay of Bengal and southeast Arabian Sea.

The European Centre for Medium-Range Weather Forecasts (ECMWF) has maintained its outlook for a basin-wide area of trough of low pressure showing up over south Bay of Bengal, equatorial Indian Ocean and southeast Arabian Sea during the whole of this week.

Towards the north, minimum temperatures slumped by 2 to 3 degrees Celsius over east Uttar Pradesh, Punjab and Haryana.

Adampur in Punjab recorded the lowest minimum temperature of 0 degree Celsius on Monday as cold northwesterlies (as against warmer westerlies) began to fill the plains tracking the movement of a western disturbance to the east.

An India Meteorological Department (IMD) forecast has said that strong northwesterly winds will prevail over Indo-Gangetic plains during the next four days.

This is expected to cause a further fall in minimum temperatures by 2 to 3 degrees Celsius over the Indo-Gangetic plains during the next three days.

For the first time this season, the IMD has warned of ground frost conditions over isolated pockets of Punjab, Haryana and west Uttar Pradesh during next three days.

Cold and chilly conditions can lift only with the arrival of the next western disturbance from across the border. The Global Forecast System of the US Fleet Meteorological Oceanography Centre has indicated the arrival of such a system around the weekend.

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