The Hindu Business Line : Heat wave in Gujarat seen as good augury

Thiruvananthapuram March 30 A minor heat wave in Gujarat and central India is the nature's way of compensating for any excess cooling that may have taken place during the winter, and bodes well for the orderly transformation of weather into pre-monsoon.

Any prolonged cooling of the North and northwest would rather have been a cause for worry, according to Dr K.J. Ramesh of the Department of Science and Technology. The heating of the plains is a must for low pressure to build and induce the monsoon currents to waft in.

But Dr Ramesh said the ongoing heating of Gujarat and central India was transient in nature and likely to ease off with the arrival of the next western disturbance. This is because the ridge (high-pressure system) along the international border has not evolved fully to be able to repel westerly systems.

The ridge should slowly give way for the seasonal anti-cyclone that presides over the extensive pre-monsoon heating from its perch over North Pakistan/West Rajasthan. So long as this does not happen, heat waves will fail to hold for any longer than the prevailing western disturbance obliges.

According to Mr Jim Andrews of AccuWeather.com, consecutive highs (in degree Celsius) of 40, 40, 42 and 41 at Surat in Gujarat (Monday to Thursday) speaks volumes on the kind of weather in those parts. "Normally hot in late March, true enough, but this is significant," he says.

Indeed, the subcontinent has been in an early heat wave since early this week. Highs of 38- to 40 degree Celsius have been common enough over the south of the country. The heat has since reached the heart of the Thar and southeastern Pakistan.

Mr Andrews concurs that the culprit in this early hot blast is the ridge aloft. Its warmth has shunted the jet stream, with its train of weather systems (lows and western disturbances) well to the north of the subcontinent.

But there will be some flattening and weakening of the ridge during the weekend, so the heat wave will get beaten back in most areas before Monday (April 2).

According to Dr Ramesh, this early heating and the `real thing' that is expected to follow would help build the `heat low' in the extreme west-northwest of the country and the required pressure gradient that would run to the south of the country.

PRESSURE DIFFERENTIAL

The southwest monsoon current that barrels into the southwest coast would use this gradient to roll `down' into the rest of the country from a region of comparatively high pressure (around Thiruvananthapuram). It will cover the entire landmass as it seeks to flow into the region of lower pressure (rendered so by the pre-monsoon heat waves).

Leading weather models that have predicted a good monsoon this year could not have failed to factor in this heating process in their models before coming out with their respective forecasts, Dr Ramesh said.

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