Monday, August 03, 2009

Monsoon subdued as ‘low’ fails to materialise

The Bay of Bengal has once again failed the forecaster community with an anticipated low-pressure area not materialising on the appointed day on Sunday. The India Meteorological Department (IMD) and the European Centre for Medium-Range Weather Forecasts had maintained their outlook for the 'low' until only two days ago.

UPPER AIR WHIRL

In its update on Sunday, the IMD traced out an upper air cyclonic circulation over northwest Bay of Bengal and neighbourhood. This would have had to descend to lower levels to set up the 'low,' but that was not to be. Satellite picture analysis suggested that the 'pull' of feverish convection and storm-building in the west Pacific may just have proved too strong for the flows to pause and set up a circulation in the Bay.

The impact was such that even westerlies heading into the north of India were made to do the bidding of the buzz in the far-east and join a large stream of eastward moisture-laden flows emptying themselves into the west Pacific.

Cyclone phase evolution analysis by at least two global models indicated that the upper air whirl may hover over the northwest Bay and Gangetic West Bengal for another three to four days. The system would still be able to anchor the ongoing rainfall regime around itself for as many days, the IMD forecast said. Fairly widespread rainfall with isolated heavy falls has been forecast over West Bengal, Sikkim, Bihar and Jharkhand during the next three days.

BUSY IN EAST

In its forecast valid until Friday, the International Research Institute (IRI) for Climate and Society at Columbia University has said that Gangetic West Bengal, adjoining Chhattisgarh and Jharkhand and parts of east Uttar Pradesh and Bihar would witness varying rain spells. Parts of east Uttar Pradesh and Bihar are expected to witness 'wetter than normal' conditions while the rains could be particularly heavy uphill over Nepal. These areas are traditionally considered vulnerable to threats of floods and landslides. A weather-friendly Madden-Julian Oscillation (MJO) wave is expected to be active over equatorial Indian Ocean from around August 15 to 23rd, though the monsoon is known to revive even without an MJO prop. The Climate Prediction Centre (CPC) of the US National Weather Services sees likely 'cyclogenesis' (birth of a storm) over southwest Indian Ocean apparently under the MJO booster impact.

SUBDUED MONSOON

The monsoon was subdued over Uttar Pradesh, Uttarakhand, Haryana, Punjab, Jammu and Kashmir, Rajasthan, Madhya Pradesh, Gujarat, madhya Maharashtra, Marathwada, Vidarbha, Chhattisgarh, coastal Andhra Pradesh and north interior Karnataka during the 24 hours ending Sunday morning.

The western end of the monsoon trough ran close to the foothills of the Himalayas, indicating the `weak phase' with sparse rainfall, if any, for central and peninsular India.

The eastern end of the trough passed through Gonda, Patna, Bankura and Sagar Islands before heading into the east-central Bay. This is what sustains the ongoing rainfall over east and northeast India.

The offshore trough from Maharashtra coast to Lakshadweep area lay extended from the Maharashtra coast to Kerala coast. It may cause fairly widespread rainfall along the west coast for three more days. Isolated heavy rain is likely over coastal Karnataka and Kerala.

The IMD has indicated subdued rainfall for the western, central and peninsular parts of the country during the next five days. But widespread rainfall with isolated heavy falls is likely over the north eastern States during this period.

A warning valid for the next two days said that isolated heavy rainfall is likely over the Northeastern States, West Bengal, Sikkim, north Orissa, Jharkhand, north Bihar, Kerala, coastal Karnataka and Andaman and Nicobar Islands.

The three days that follow will see fairly widespread to widespread rainfall over the northeast and adjoining east India as well as along the foothills of the Himalayas.

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