Thursday, April 28, 2011

Heating of land apace in northwest India

A forecast outlook from India Meteorological Department (IMD) indicates that the summer heating of extreme northwest India has started in right earnest.
Arrival of a spoilsport western disturbance has been factored in, but its influence would not extend beyond Jammu and Kashmir and Himachal Pradesh. Mainly dry weather is expected to prevail over the plains of northwest and adjoining west and central India.
The westerly system would be able to do no more than cap the heating trend in the northwest, according to the outlook.
Strong surface winds would prevail over Gujarat, Rajasthan and the Indo-Gangetic plains until Friday. No significant change in temperatures is seen over parts of the plains of northwest India and adjoining central and west India until Friday, the IMD said.
Meanwhile, maximum temperatures recorded on Tuesday ranged between 40.0 deg Celsius to 44.0 deg Celsius at many parts of Rajasthan, west Madhya Pradesh, north Gujarat and Vidarbha.
Global models had indicated earlier that the core heating would cross the northwest border into the western parts of India from this week. This is where the ‘heat low’, a peculiar phenomenon triggered by sustained heating of the land surface develops locally.
This in turn leads to the creation of an elongated area of lower pressure extending from the West Asia desert across Pakistan and into northwest India. This is unlike the usual pattern when heating of the land assumes the sinking motion of air and therefore higher pressure.
The ‘heat low’ is a crucial cog in the wheel of the monsoon system, helping draw, as it would, moisture-laden southwesterly winds from the Arabian Sea and the Bay of Bengal.
Even as the northwest is heating up, the IMD said maximum temperatures were below normal by 2 to 6 deg Celsius over Gangetic plains and Tamil Nadu on Wednesday.
They were near normal over rest of the country except parts of Assam, Meghalaya, Arunachal Pradesh and interior Maharashtra where they are above normal by 2 to 3 deg Celsius. The highest maximum temperature of 45.2 deg Celsius was recorded at Ganganagar in Rajasthan.
During the day on Tuesday, scattered rain or thundershowers occurred over Tamil Nadu and Jharkhand and isolated over east Uttar Pradesh, sub-Himalayan West Bengal, Sikkim and Kerala.
Satellite imagery early on Wednesday morning showed the presence of convective (rain-driving) clouds over parts of south and east-central Bay of Bengal, Assam, Nagaland, Manipur and southeast Arabian Sea.
The IMD traced a trough extending from west Rajasthan to southwest Bay of Bengal across interior Maharashtra, interior Karnataka and Tamil Nadu with embedded upper air cyclonic circulations over west Madhya Pradesh and southwest Bay of Bengal.
Another trough lay extended from an upper air cyclonic circulation over west Madhya Pradesh and ‘telescoped’ into a counterpart circulation over Gangetic west Bengal. In the process, the trough passed over east Madhya Pradesh, north Chhattisgarh and Jharkhand.
A weather warning said that isolated thunder squalls would occur over Jharkhand, Orissa, West Bengal, Sikkim and the Northeastern States until Friday.
A short-term outlook said that fairly widespread rain or thundershowers would occur over Andaman and Nicobar Islands and Lakshadweep until Friday. Scattered rain or thundershowers may break out occur over south and coastal Karnataka, Kerala and Tamil Nadu during this period.
Scattered rain or thundershowers would unfold over the Northeastern States, West Bengal, Sikkim, Jharkhand, Orissa and Chhattisgarh. It may relent later over Jharkhand and Chhattisgarh from Friday.
Isolated rain or thundershowers are likely over Jammu and Kashmir and Himachal Pradesh from Friday.
An extended outlook until Sunday said that scattered rain or thundershowers would occur over northeast and adjoining east and south peninsular India. 

No comments:

Post a Comment