Wednesday, August 11, 2010

Monsoon easterlies being eased out from north-west

Westerly flows have started filling North-West India by easing out monsoon easterlies in the build-up to what is thought to be a ‘break monsoon' condition, or an intra-seasonal weakening trend in rainfall.
Break monsoon condition comes about in association with the northward shift of the monsoon trough from its normal position over Gangetic plains towards the foot of the Himalayas.

OTHER FEATURES
The monsoon westerlies in the lower troposphere extend right up to the rim of the Tibetan Plateau, a process that has been set already in motion over the Northwest.
Two other features – eastward movement of the westerly trough with large amplitude extending into West Pakistan and North India, and a high-pressure region over Arabia protruding into Central and Peninsular India – are also indicated, though not conclusively so.
During a break monsoon, heavy to very heavy rain is to be expected along the Himalayan foothills and Northeast India, and to some extent over parts of East and South-East India as well.
But the rainfall is comparatively muted along the west coast, if not entirely shut out.

TROUGH TO SHIFT
An India Meteorological Department (IMD) update said on Tuesday that the western end of monsoon trough is likely to shift northwards during the next two days.
It is expected that the eastern end would also follow suit in another three days' time for the trough to move entirely to the foothills.
A warning valid for the next two days said that isolated heavy rainfall would occur over Jammu and Kashmir, Himachal Pradesh and Uttarakhand in accordance with the proximity gains vis-à-vis the incoming monsoon trough.
The 24 hours ending on Tuesday afternoon saw fairly widespread rainfall being reported from the Western Himalayan region.
It was scattered over Madhya Pradesh, East Rajasthan, the West Coast and the coastal areas of Orissa and West Bengal.

CONVECTIVE CLOUDS
Satellite pictures on Tuesday showed the presence of convective (rain-bearing) clouds over parts of the Western Himalayas, north-west, East and Northeast India, the Bay of Bengal, Andaman Sea and north-east Arabian Sea.

LOW PRESSURE AREA
An IMD outlook for Tuesday indicated the possibility of a feeble low-pressure area materialising over north-west and adjoining West-central Bay of Bengal under the influence of a persisting upper air cyclonic circulation.
Forecast for the next three days said that fairly widespread rain or thundershowers would occur over the Western Himalayan region during the next 24 hours and increase in intensity thereafter.

WIDESPREAD RAIN
Fairly widespread rain or thundershowers would occur over East Uttar Pradesh, Bihar, Konkan, Goa, Coastal Karnataka, Kerala, Sub-Himalayan West Bengal, Sikkim, the north-eastern States and the Andaman and Nicobar Islands.

EXTENDED FORECAST
Scattered rain or thundershowers has been forecast over Punjab, Haryana, Delhi, West Uttar Pradesh, Central and East India during next 24 hours before scaling up in intensity.
Extended forecast until Sunday said that widespread rainfall with isolated heavy to very heavy fall would occur over the Western Himalayan region and adjoining northern plains.
Fairly widespread rainfall has been forecast for Central and East India.

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