Thunderstorms regrouping over North-West, South, and East Coast

After a lean patch from March 26 to April 4, thunderstorms are resuming activity over the South Peninsula to likely grow more intense from mid-April until the month-end. The ongoing week (April 5 to 14) would mark the transition to a more fulsome and productive 10 to 15 days till April 30, according to the US Climate Forecast System (CFS) model.

A few other models indicate the possibility of South India with the Bay of Bengal joining in the party and pushing a wave of rain into Tamil Nadu just ahead of April 15. This would happen after thunderstorms spawning from the West along the Kerala coast move towards South Interior Karnataka and Tamil Nadu.

Wind discontinuity

India Meteorological Department (IMD) attributes this to the presence of a wind discontinuity or trough, a prominent pre-monsoon feature over South India, capable of generating thunderstorms, lightning and gusty winds during the next three days. Isolated heavy rainfall is also likely over Coastal and South Interior Karnataka, Tamil Nadu, Puducherry and Kerala till tomorrow (Tuesday).

To the North-West, the IMD saw western disturbance activity building in right earnest with at least two such disturbances expected to check in one after the other. This is even as an existing system is readying to leave the country to the East and away.

Western disturbances

These disturbances travel all the way from the Mediterranean to Iraq, Iran, Afghanistan and Pakistan before reaching North-West India and amplifying weather during winter and spring. They bring thundershowers accompanied often with lightning, hail and high winds in line with the heating up of land.

The latest one was moving over Iran on Monday to Afghanistan, but will induce the formation of a cyclonic circulation over Central Pakistan and adjoining West Rajasthan by tomorrow (Tuesday). Cyclonic circulations get induced depending on the strength of the parent, making it an active one. The IMD sees a follow-up disturbance affecting the hills of North-West India from Thursday (April 9).

These systems will jointly drive the weather across North-West India to a peak from Tuesday to Thursday, with scattered to fairly widespread rain/thundershowers over the hills (Jammu & Kashmir,Himachal Pradesh and Uttarakhand), Punjab and Haryana, Chandigarh and Delhi. Isolated thunderstorm accompanied with lightning, hail and gusty winds (speeds reaching 30-40 km/hr) are also likely over these places.

Scattered to fairly widespread rainfall/thunderstorms are likely over North-East India on Wednesday and Thursday and isolated squalls over Assam, Meghalaya and Nagaland, Manipur, Mizoram and Tripura Tuesday and Wednesday. Isolated to scattered rainfall/thunderstorms accompanied with lightning are likely over East India also during this period.

Rainfall pattern

Productive western disturbances through this winter and spring have ensured that the rainfall for the country as a whole remain above normal by 28 per cent till date during the season (March 1 to April 4). Only South Interior Karnataka; Tamil Nadu & Puducherry; Konkan & Goa; and a few North-Eastern States are in varying deficit. The rest of the country have received excess or mostly large excess rainfall during this period.

Rains are also expected to materialise along the East Coast and adjoining East India during the next few days as the western disturbances start moving to Central India (especially Madhya Pradesh) and the rest of East-Central India. The US National Centres for Environmental Prediction agrees, and points to rain-bearing clouds forming over South India, the East Coast, and North-West India. Only regions outside of the rain wave would be South-East Rajasthan, Gujarat, West Madhya Pradesh and West Maharashtra.

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