Unstable weather forecast across country over weekend

Prevailing weather across the country is poised to get unstable with Cyclone Phyan remnant dictating terms over the north as does an incoming easterly wave to the south.

This includes the possibility of moderate to intense fog over the plains during and after the weekend, India Meteorological Department (IMD) said in its outlook on Friday.

MORE RAIN

Phyan may have been reduced to an upper level circulation but is combining with an itinerant western disturbance to still rain over parts of central and east India.

The Phyan remnant will continue to track to the east, driven by the dominating westerly flows. But pushing in from its rear is the western disturbance that features an induced cyclonic circulation over Rajasthan/Gujarat.

This cyclonic circulation is in turn pulling in from the Arabian Sea, triggering the formation of a trough extending from east-central Arabian Sea to west Rajasthan.

The IMD has predicted that the moisture incursion from the Arabian Sea would cause isolated to scattered rain/thundershowers over northwest India until Monday. Moderate to intense fog would be triggered wherever the moisture build is not enough to cause precipitation.

Meanwhile, on Friday, the IMD also located a fresh low-pressure area over southwest Bay of Bengal and its neighbourhood. International models had pointed to building activity over this region from the last week itself.

The sea-surface temperatures continue above the threshold levels in the region, supported by an eastward-transiting wet phase of the Madden-Julian Oscillation (MJO) wave, which can influence weather on ground.

The Climate Prediction Centre (CPC) of the US National Weather Services feels that the MJO wave would be active until Monday, before it moves further east into the western Pacific.

DRY MJO WAVE

Dedicated MJO tracking models - except one - aver that the dry phase would kick in as early as from Tuesday but may not impact the monsoon weather on ground significantly at least this time round.

The MJO can cease to be of much influence after the northeast monsoon - southwest or, in this case, northeast - entrenches and reaches a stage where it can sustain on its own. What it needs is convection in the seas, resultant moisture and winds, which the seasonal weather dynamics provide for.

International precipitation models too suggest that the southeast and southwest Bay would continue to be active even after the MJO wave exits. Resultant rains are forecast to impact Sri Lanka, southeast Tamil Nadu and Kerala.

Intervening western disturbances would cause the moisture being pumped in by the easterlies to be fanned east-northeast over the peninsula.

The US National Centres for Environmental Prediction (NCEP) sees the entire peninsula getting wet in this manner during the next week.

MORE LOWS

According to the ECMWF, easterly waves may be able to sustain the southerly rain regime towards the month-end replete with the possibility of fresh low-pressure areas.

The IMD update on Friday said that scattered to fairly widespread rainfall has occurred over parts of plains of northwest India, central India, and coastal areas of Orissa and north Andhra Pradesh.

Satellite imagery showed convective clouds over parts of south Bay of Bengal, Uttar Pradesh, Uttarakhand and Jammu and Kashmir.

Scattered to fairly widespread rainfall with isolated heavy falls is likely over Tamil Nadu and Kerala during next three days. Scattered rainfall activity is also likely over the Northeastern States from Sunday.

A warning valid for next two days said that isolated heavy rainfall is likely over Tamil Nadu and Kerala.

An update from the Regional Met Centre, Chennai, said that rain or thundershowers are likely at a few places over Tamil Nadu, Puducherry and Kerala.

Isolated rain or thundershowers are likely to occur over Karnataka, Andhra Pradesh and Lakshadweep.