India Meteorological Department (IMD) has said heavy rain (≥7 cm) may lash isolated places over the South Peninsula across Tamil Nadu, Puducherry & Karaikal and Kerala & Mahe on Sunday as a trough of low-pressure parked itself off the Tamil Nadu coast. Thunderstorms accompanied with gusty winds, and lightning may prevail at isolated places over the region. 

Scattered light to moderate rain accompanied with heavy rain, thunderstorms and lightning is likely at a few places over south interior Tamil Nadu and south Kerala. The US Climate Forecast System saw a varyingly light to moderate wet cover sustaining over parts of the South Peninsula (Kerala, Tamil Nadu and Karnataka) for rest of January, and even into early February. 

Numerical model forecast

The Ensemble Prediction System that incorporates projections by various numerical models said South Peninsula would be a beneficiary of spillover rain from easterly waves/troughs originating in the Gulf of Thailand/Sumatra regions and travelling in a towards the Sri Lanka coast. The island nation is expecting heavy to very heavy rain from these systems over next few days.

To the north, a western disturbance in the form of a weather-making trough of low pressure across the tri-junction of Iran-Afghanistan-Pakistan borders is interacting with a counterpart trough in easterlies extending from Gujarat to north Rajasthan in the east, to set off isolated to scattered rain/snow for three days over the hills (Himalayas) of North-West India until Tuesday.

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Western disturbance moving in

As the trough moves east and continues to interact with southeasterly winds from the Bay, distribution and intensity of rain/snow may increase over the hills, apart from triggering a rain spell over the plains of the region from Tuesday to Thursday. Isolated to scattered rain is forecast over Punjab, Haryana and Chandigarh during these days; over Rajasthan on Wednesday; and West Uttar Pradesh on both Wednesday and Thursday. Isolated heavy snow is predicted for Uttarakhand on Thursday. 

Cold spell over North

Warmth associated with clouds and moisture associated with a western disturbance is bitterly lacking over North-West India, which has once again triggered a cold spell over the region. This may be lifted over the next 3-5 days as the incoming western disturbance starts to impact weather. The IMD said minimum (night) temperatures are below 0°C over many parts of Jammu, Kashmir & Ladakh; 2-5°C over some parts of Himachal Pradesh; 6-12°C over North-West and Central India;12-16°C over East and West India. The lowest minimum on Saturday of 5.0°C over the plains was reported at Bulandshahr (West Uttar Pradesh). 

Rainfall scenario

The rainfall scenario since the dawn of the New Year fails to inspire confidence over Central India (a deficit of -94 per cent until Saturday), while it has improved over North-West India, the South Peninsula, and East and North-East India. While Central India continues to wallow at the bottom of the rainfall sweepstakes, the deficit is -35 per cent over East and North-East India; 51 per cent over South Peninsula; and -67 per cent over North-West India till Saturday, the IMD said.