Weather: Thunderstorms to scale up over South Peninsula from tomorrow

Rainfall activity over the the South Peninsula is expected to increase from tomorrow (Thursday) and stay as such for the next three to four days as the pre-monsoon thunderstorm activity intensifies. The India Meteorological Department (IMD) has forecast thunderstorms, lightning, gusty winds and heavy rainfall over these region during this period.

The Thiruvananthapuram Met Office has forecast thunderstorms accompanied with gusty winds with speed reaching 30-40 km/hr at one or two places in Kerala from Wednesday to Sunday. This flare-up is usual during this time of the year ahead of the en masse movement of a band of rain-bearing clouds to the East and South-East and into the Bay of Bengal.

Churn in the Bay of Bengal

This will in turn initiate churn in the Bay about which some global models have given advance notification, and the IMD wind profile maps maintains a lookout for. A low-pressure area, the first of the pre-monsoon season, may pop in the South-East Bay and adjoining Andaman Sea by the month-end. This is also in line with the usual pattern of weather during this time of the year in the Bay.

Meanwhile, the IMD has also pointed to the ongoing enhanced thunderstorm activity over East and North-East India, another seasonal feature during the pre-monsoon season. Isolated heavy rainfall, thunder squalls and hailstorms have been forecast over the North-Eastern States during next two days; and over Odisha and plains of West Bengal until for tomorrow (Thursday).

Volatile weather in East India

What works behind the volatile weather over the North-East is the inward movement of western disturbances from North-West India. The IMD has said that the latest disturbance on show will spark isolated to scattered rainfall with isolated hailstorm over Himachal Pradesh, Uttarakhand, Punjab, Haryana, Chandigarh, Delhi and West Uttar Pradesh on Thursday. This is even as incursion of opposing moisture-laden winds from the Bay North-East and adjoining East India continues unabated for the next 4-5 days.

Dry north-westerlies from the western disturbance run into densely wet winds from the Bay triggering fairly widespread to widespread rainfall/thundershowers for as many days. These are called Nor’westers (north-westerlies, also called regionally as Kalbaishakhi or Bordoisila) and affect the neighbouring Bangladesh as well.

Tornado season

The Nor’westers often pack violent hurricane-speed winds across the rugged terrain of the North-East. Depending on the amount of moisture mopped up from the Bay, convection (process of cloud-building) and high winds, they can even spew dangerous tornadoes. The high winds, thunderstorm and lightning occur just before sunset or just few hours after it, when thick dark black clouds start building over the south-western sky and breaks into torrential rain often with hail but only a short period of time.

Forecast for today (Wednesday) said thunderstorms accompanied with lightning and squall (wind speed reaching 60-70 km/hr) may lash parts of Assam, Meghalaya, Nagaland, Manipur, Mizoram and Tripura. Lightning and squall (wind speeds reaching 50-60 kmph) are forecast over the plains of West Bengal.

Thunderstorms accompanied with lightning & gusty winds (speed reaching 40-50 km/hr) are likely at isolated places over hills of West Bengal and Sikkim; with lightning and gusty winds (speeds reaching 30-40 km/hr) over Odisha and Arunachal Pradesh; and with lightning over Chhattisgarh, East Madhya Pradesh, Vidarbha, Bihar, Jharkhand, Coastal Andhra Pradesh, Interior Karnataka, Tamil Nadu, Puducherry, Kerala, and Telangana. Heavy rainfall is likely at isolated places over Arunachal Pradesh and Nagaland, Manipur, Mizoram and Tripura.

Forecast for tomorrow

Thunderstorms accompanied with lightning and squall (wind speeds reaching 60-70 km/hr) are forecast tomorrow (Thursday) over Nagaland, Manipur, Mizoram and Tripura; with lightning, hail and gusty winds (wind speeds reaching 40-50 km/hr) over West Bengal, Sikkim, Assam and Meghalaya; and with lightning, hail and gusty winds (speeds reaching 30-40 km/hr) over Himachal Pradesh, Uttarakhand, Punjab, Haryana, Chandigarh, Delhi, West Uttar Pradesh, Telangana, Uttarakhand, Chhattisgarh and Madhya Pradesh.

Thunderstorms accompanied with lightning and gusty winds (speed reaching 30-40 km/hr) are also forecast over Vidarbha, Kerala, East Uttar Pradesh; and with lightning at isolated places over Bihar, South Interior Karnataka, Jharkhand, Coastal Andhra Pradesh and Rayalaseema. Heavy rainfall is likely at isolated places over Nagaland, Manipur, Mizoram and Tripura. Dust storm/thunderstorm accompanied with gusty winds (speed reaching 30-40 km/hr) is likely at isolated places over Rajasthan.

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