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Vinson Kurian

Thiruvananthapuram, Nov. 29

Isolated rain has been reported over Tami Nadu during the 24 hours ending Sunday morning, with the heaviest falling over the southeast coast.

This could be the harbinger of a wet regime that could slowly begin to assert itself over the southern peninsula during the first week of December and possibly into the second, says the US National Centres for Environmental Prediction (NCEP).

The weak north-east monsoon conditions are likely to continue over south peninsular India during the next 36 hours ahead of a slight increase in rainfall activity thereafter, an outlook posted by India Meteorological Department (IMD) said on Sunday.

Isolated to scattered rains have been forecast over the region until Wednesday, up to which forecasts were available.

Low in making?

A couple of international models have been suggesting the formation of a low-pressure area being triggered over southeast Bay of Bengal and travelling west towards southwest Bay of Bengal during this period.

A shorter-term outlook for the next two days by the Regional Met Centre, Chennai, said that rain or thundershowers are likely at a few places over coastal Tamil Nadu and Puducherry.

Isolated rain or thundershowers has been forecast for interior Tamil Nadu and Lakshadweep. The short-term outlook is based on the expected behaviour of a slow-moving, westward-bound cyclonic circulation over southeast and adjoining southwest Bay of Bengal.

The US Navy's NGP model that tracks movement of cyclonic circulations showed the southwest Bay of Bengal system moving south of Sri Lanka and heading towards southwest Arabian Sea.

But, the Canadian Meteorological Centre (CMC) has suggested the possibility of another system being generated from the deep south of Gulf of Thailand crossing into the Bay of Bengal and funnelling towards Tamil Nadu coast during November 29 to December 5.

In CMC's view, it is likely to be a cyclonic circulation, not amounting to a low-pressure area as suggested by other models.

The NCEP's precipitation forecast chart too shows a ‘blow-up' of rains over the Tamil Nadu coast during the week beginning December 7.

MJO BOOSTER

The wet session could likely get a boost from an incoming wet phase of the Madden-Julian Oscillation (MJO) wave (the alternating dry phase with suppressed rain is currently active over the region) that travels in the upper levels of the atmosphere from the west to the east.

Of a set of three leading MJO wave tracker models, two were of the view that it would be active after December 8 over the equatorial Indian Ocean and adjoining Arabian Sea and Bay of Bengal. The third one saw it coming delayed by four to five days.

But the wave could extend its influence over local weather as late as beyond the dawn of the New Year, according to the longer term projections by one of these models.

Meanwhile on Sunday, satellite imagery showed presence of convective clouds over parts of south Bay of Bengal and south Arabian Sea.

Cold in north

In the north, minimum temperatures are below normal over parts of Marathwada, Vidarbha, north interior Karnataka, Telangana, coastal Andhra Pradesh, Orissa, Chhattisgarh, Jharkhand and east Uttar Pradesh, the IMD said.

The lowest minimum temperature of 3.9 deg Celsius was recorded at Amritsar in what is an improvement over the sub 3-deg Celsius level recorded the previous day. This is being ascribed to the presence of the ‘steaming head' of a prevailing western disturbance.

The IMD has also declared the lookout for the arrival of a fresh western disturbance over the western Himalayan region on Monday and Tuesday. Isolated to scattered precipitation has been forecast here during this period.

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