Another Low Pressure Area Around August 29? New Weather System May Put Mahanadi Basin Back on Flood Watch| Exclusive

Bhubaneswar: Just as the current low-pressure area is expected to move across central and western Odisha, forecast models are indicating the possibility of another low-pressure system forming around August 29, raising the prospect of a renewed flood threat for the Mahanadi basin.

The danger lies not in any single weather system, but in the back-to-back sequencing of two lows.

The first low, currently over the northwest Bay of Bengal, is expected to move across central and coastal Odisha before shifting west-northwest towards western Odisha and Chhattisgarh. This could bring significant rainfall over both the downstream and upstream parts of the Mahanadi system.

Then comes the second weather system.

How It will Pan Up?

Forecast guidance of reputed significant weather forecasters like National Centre For Medium Range Weather Forecast (NCMRWF), European Centre for Weather Forecast (ECMWF) and NCICS points to the formation of another low-pressure area around August 29-30, with a more active monsoon phase developing over the Bay of Bengal and eastern India.

The system is projected to evolve around the Head Bay of Bengal, potentially producing another widespread spell of heavy rainfall over eastern and central India.

For the Mahanadi basin, this timing could become crucial.

Why All Eyes on Mahanadi?

The first system is expected to load the upstream catchments in western Odisha and Chhattisgarh with heavy rain, increasing runoff into the Hirakud and Mahanadi system. At the same time, it could also bring heavy rainfall to the downstream coastal-central plains.

If another low forms around August 29, the concern is that a fresh spell of widespread rainfall could arrive before the river system fully drains the runoff generated by the first system.

That creates what could be called a catchment-to-delta flood trap.

The first low could saturate the western and upstream catchments. As the resulting runoff moves downstream, the second low could bring another round of rain over central and coastal Odisha.

In such a scenario, the Mahanadi system would face pressure from both incoming upstream discharge and fresh local rainfall over the downstream basin.

This is why the projected second low around August 29 holds significance for Odisha's flood outlook.

The issue is not merely how much rain falls under the second system. The more important factor will be where the rain falls and when it arrives relative to the runoff generated by the first low.

Back-to -Back Low Threat

If the first system substantially loads the Mahanadi catchment in western Odisha and Chhattisgarh, and the second system subsequently delivers widespread rain over central and coastal Odisha, the river channels and drainage systems could face a much tighter situation.

Forecast guidance currently suggests that the second system could form further north around the Head Bay of Bengal and intensify the active monsoon phase towards the end of August. But the exact rainfall distribution and track (suggest northwest movement as of now) will be crucial in determining the eventual flood impact.

Why North Odisha On Watch Again?

There is also a separate concern for northern river basins if the second system tracks, as per NCMRWF Forecast, closer to north Odisha, West Bengal and southern Jharkhand. Such a track could increase rainfall over the catchments of the Brahmani, Baitarani and Subarnarekha as well.

For now, the immediate system may spare flood-hit north Odisha from a fresh weather blow. But the August 29 window is emerging as the next key date to watch.

The Mahanadi flood threat will depend on whether the second low materialises as projected and whether its rainfall arrives over the downstream basin while the runoff pulse from the first system is still moving through the river network.

That is the real flood risk equation: one low loading the catchment, followed by another weather system arriving before the Mahanadi basin gets enough time to drain. 

Also Read: Low Forms Over Bay, But Flood-Hit North Odisha Gets a Breather; Heavy Rain Shifts to Mahanadi Belt| Exclusive