National weather: Rogue thunderstorms may raid parts of Tamil Nadu, Kerala

Active North-East monsoon conditions may have exited the South Peninsula but model forecasts suggest that rogue thunderstorms coming in from around the Sri Lankan seas could hit some areas in Tamil Nadu and Kerala during the rest of December.

The India Meteorological Department (IMD), New Delhi, has already forecast the possibility of heavy rainfall breaking out at isolated places in Tamil Nadu, Puducherry and Karaikal on Thursday. Going forward, the IMD-Global Forecast System (GFS) sees more wet weather materialising over the southern parts of Kerala and Tamil Nadu, heavy at times.

The IMD has forecast heavy rainfall breaking out at isolated places over Tamil Nadu, Puducherry and Karaikal on Thursday. The dark clouds seen in Chennai on Monday morning portend more rainy days for the region.

Dip in night temperatures

Minimum (night) temperatures have fallen at a number of places in North-West India after an active western disturbance weakened and exited the country to the East-North-East. Remnants of moisture left behind by the system have cooled and condensed into fog to dense fog enveloping the region in the morning hours, from the North-West to East India.

An IMD outlook on Monday said that shallow to moderate fog will hang over isolated pockets of Madhya Pradesh and parts of East and North-East India during the next two or three days. Minimum (night) temperatures are expected to fall gradually by over 2-4°C over East India during this period, as the skies clear up there as well. Extended outlook from December 25 to 28 hinted at the possibility of isolated to scattered rain/snow over the hills of North-West India. Isolated rainfall is likely over parts of the South Peninsula (mainly Tamil Nadu) and the islands.

The mercury would drop further with cooler Arctic air filling the region and the skies clearing up along the track of the away-moving western disturbance. The moisture from the western disturbance sets up the clouds, which prevents the cold air from seeping in from the upper levels. With the clouds gone, the dense cold air weighs in over the ground, bringing down the mercury.

On Monday, a winter haze was observed in a number cities in West and Central India, including Mumbai. Photo: Paul Noronha

 

Feeble western disturbance

The next western disturbance with its steam engine upfront (moisture carrying) and warm, moisture-laden air rising to form clouds alone can break the cold. A follow-up western disturbance expected to arrive over the hills of North-West India may not, however, have what it takes to alter the weather in the plains. It would at best trigger snow and thunder-showers along the hills, but not do much over the plains. An IMD update indicated how the clearing skies brought down the day temperatures during the 24 hours ended Monday morning at a number of places in the region.

Day temperatures were markedly below normal at most places over Madhya Pradesh; at a few places over Jammu & Kashmir, Rajasthan and Bihar and at isolated places over Himachal Pradesh, Haryana, Chandigarh, Delhi and the hills of Bengal and Sikkim; appreciably below normal at most places over Gujarat and at a few places over Punjab and Uttar Pradesh; below normal at most places over Saurashtra and Kutch and at isolated places over Konkan and Goa, Gangetic West Bengal and Lakshadweep; and near normal over the rest of the country.

Continued clear skies would mean the cold conditions may continue with fog to dense fog drifting across North-West India and adjoining West and Central India, apart from East and North-East India. On Monday, a winter haze was observed in a number cities in West and Central India, including Mumbai.

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