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Vinson Kurian

Thiruvananthapuram, July 17 A classical ‘weak monsoon’ phase has set in with rainfall being confined to the extreme east and northeast and along the west coast of the country.

The northwest, central and the interior peninsula are witnessing subdued activity that is expected to continue for at least another few days, said Dr Akhilesh Gupta, Advisor to the Department of Science and Technology.

The subdued conditions will feature a minor change during the subsequent five days. The ‘change’ will be provided by a spurt in rainfall activity over Tamil Nadu, again a feature associated with weak monsoon. Rains are expected to begin around July 23 in these parts and will continue for at least 10 days.

The weak phase could end sooner, or last unduly longer, depending on the unravelling of two milestone events – development of a tropical disturbance in the Bay of Bengal or the initiation of the next monsoon-friendly Madden-Julian Oscillation (MJO) wave, in that order.

According to Dr Gupta, the Bay can buzz back to life with the formation of the next ‘low’. This can happen in two ways – an ‘in situ’ system developing within the basin or a migrant coming from the east (South China Sea/West Pacific).

The monsoon trough having retreated to the Himalayan foothills rules out an ‘in situ’ system developing any time soon. There is no indication either of a migrant system reaching the Bay to set up a ‘low’ although some models suggest that Typhoon Man-Yi that hit Japan last Saturday might just be able to spring up a surprise. But this is only a remote possibility.

The MJO is one of the world’s key large-scale atmospheric circulations that regulate the intensity and breaking of rainfall associated with the Indian monsoon. The MJO is a large-scale eastward movement of air in the upper troposphere with a period of about 20-70 days, over the tropical eastern Indian and western Pacific Oceans.

The MJO is the main fluctuation of atmospheric circulation that explains variations of weather in the tropics and regulates the monsoon. It is believed to have aided the ‘bull run’ of the monsoon after Super Cyclone Gonu rendered it asunder earlier in June. The variation of the MJO involves variations in wind, sea-surface temperature, cloudiness, and rainfall.

Mr Jim Andrews of AccuWeather.com says that the broad-scale upward motion associated with an MJO, and spread over South Asia, is fading eastward. A belt of ‘sinking air’ is on the way in from Africa, which signals ‘drying up’ of the landscape. It kills any prospect of systems forming in the nearby seas.

According to Mr Andrews, the return of a broad-scale upward motion from the west is suggested for late August only. In this manner, the monsoon has reached a stage where the revival could take weeks to accomplish in the absence of the Bay responding in kind sooner.

Meanwhile, Monday’s well marked ‘low’ over Bihar and adjoining Jharkhand lay over east Uttar Pradesh and adjoining Bihar on Tuesday. Under its influence, widespread rainfall with isolated heavy to very heavy falls is likely over east Uttar Pradesh, Bihar and Sub-Himalayan West Bengal and Sikkim during next three days. These are all rain-deficit areas as per latest India Meteorological Department (IMD) tally.

The current meteorological analysis suggests that widespread rainfall with isolated heavy to very falls is likely over the Northeastern States during the next five and over Kerala, Lakshadweep and coastal Karnataka during the next three days, an IMD update said.

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