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Vinson Kurian

Thiruvananthapuram April 3 A passing western disturbance and northwesterly winds that blew in its wake have helped bring the mercury level in North India, after seasonal changes in leading weather features along the international border threatened to heat up the plains early this season.

But no such relief is being predicted for South India, where the traditional `hot spots' have already started warming up.

For instance, Kadapa in Andhra Pradesh has been recording persistently high temperatures of around 40 deg C for some time now.

According to Mr Jim Andres of AccuWeather.com, the leading edge of the 38-degree C heat reached to the foothills in Nepal.

On Wednesday, he picked out the hot spot of Nagpur at 42.3 deg C for having warmed up early and abruptly.

RIDGE SITTING

The leading seasonal attribute presiding over regional weather is the `ridge' of high pressure sitting over South Pakistan and adjoining West Rajasthan. The dry, sinking air associated with a high-pressure area (as against the rising, moist air in a low-pressure system) generates clear skies and fair weather.

Western disturbances that manage to march past the ridge and drift across the border head in a north-northeast direction in India to cover the plains and the northeast.

Only those with exceptionally high amplitude manage to dip into the south, bringing associated weather to North Peninsular India But they are hard to come by during this time of the year.

What the ridge essentially does is to deflect the sub-tropical jet stream and its train of weather heads (lows, western disturbances cyclones) to latitude north of India's.

Jet streams are rivers of wind high in the atmosphere - above about 20,000 feet - that steer storms.

They also help determine the locations of areas of high and low air pressure at the earth's surface.

SOUTH HEATS UP

The somewhat flattened ridge (after having been impacted by the western disturbance) may spare the North the heat for sometime, but will ensure that the sun oppresses the southern half of the country.

Many places in Tamil Nadu and Andhra Pradesh have already crossed the 100 deg Fahrenheit threshold (37.8 deg C).

On Wednesday, the maximum temperature rose at some places in Telengana, Rayalaseema and interior South Karnataka.

They were appreciably above normal at many places in Tamil Nadu, Karnataka and Kerala as well.

There seems no respite for them except from the outbreak of isolated thundershowers from locally intensive heating and convection.

The Inter Tropical Convergence Zone (ITCZ), a global band of `low' that drives wet weather, is located far beyond the tip of the landmass to be of any relevance.

More Stories on : Climate & Weather | Climate & Weather | Outlook

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