Deep Depression Meets Western Disturbance: The Weather Collision Behind Uttar Pradesh's Deluge

Uttar Pradesh has witnessed intense rainfall over the past few days, leaving several districts facing flood-like conditions. The downpour has disrupted normal life, damaged houses and crops, and triggered rain- and storm-related incidents across the state.

Between September 25 and the morning of September 27, 56 people died and 46 were injured in rain- and storm-related incidents, according to data shared by the state’s Office of Relief Commissioner, reported The Indian Express.

Official figures showed that 1,021 houses were damaged during the period. Heavy rain was reported in Kanpur, Varanasi, Prayagraj, Gorakhpur, Bareilly and several other parts of Uttar Pradesh, accompanied by winds reaching 30-40 kmph.

The state received 45.1 mm of rainfall in the 24 hours ending Sunday, against the normal 1.8 mm. As many as 56 of its 75 districts recorded excessive rainfall.

The India Meteorological Department (IMD) said the intense rainfall was likely linked to the interaction of two weather systems - a deep depression that originated over the Bay of Bengal and a Western Disturbance over northwestern India.

Low-pressure Weather System

A deep depression is an organised low-pressure weather system that can produce strong winds and heavy rainfall.

In its September 26 press note, the IMD said the deep depression formed over the Bay of Bengal and crossed the North Andhra Pradesh-South Odisha coast before weakening. It was subsequently centred over north-eastern Madhya Pradesh and adjoining south-eastern Uttar Pradesh.

A low-pressure system develops when atmospheric pressure in an area is lower than in surrounding regions. Air moves towards the low-pressure area and rises. Moist air can cool as it rises, causing condensation, cloud formation and rainfall.

The IMD said depressions can bring strong winds and heavy rain. As a system weakens into a well-marked low-pressure area, its intensity and wind speeds decline, reducing rainfall activity.

On September 27, the IMD said the system had moved north-northwestwards and weakened into a well-marked low-pressure area at 5.30 am. It was expected to continue moving across Uttar Pradesh and weaken further into a low-pressure area over the next 12 hours.

As per September 27 note, IMD also said the likely interaction of the deep depression with a Western Disturbance could produce strong gusty surface winds and heavy to very heavy rainfall in parts of Uttar Pradesh.

It forecast isolated extremely heavy rainfall in the central Terai belt and exceptionally heavy rainfall of more than 30 cm at one or two places.

How Intense Was The Rainfall?

The IMD's Uttar Pradesh daily weather report said western Uttar Pradesh received light to moderate rainfall with isolated heavy to very heavy rainfall at most places in the 24 hours ending 8.30 am on September 27.

Eastern Uttar Pradesh recorded light to moderate rainfall with isolated heavy to extremely heavy rainfall at most places. Thunderstorms with lightning and gusty winds were also reported at isolated places.

Kaimganj in Farrukhabad recorded 32 cm rainfall, the highest, followed by Birdghat in Gorakhpur at 23 cm. Nighasan in Kheri and Trimohani Ghat Fmo in Maharajganj recorded 19 cm each, while Gorakhpur and Bilari in Moradabad received 18 cm each.

Bareilly CWC, Aonla and Bareilly PBO recorded 17 cm each, while several locations recorded 15-16 cm.

Day temperatures also fell across several districts. The highest maximum temperature recorded on September 26 was 28°C at Churk, while the lowest minimum temperature on September 27 was 18.4°C at Orai.