EXCLUSIVE|Bay of Bengal Cyclogenesis Faces Big Hiccup Near Odisha-Andhra Coast: Heavy Rain More Likely Than Severe Cyclone

Bhubaneswar: The developing cyclonic circulation over the Bay of Bengal may find the open sea increasingly supportive for intensification, but its biggest test could come precisely when it approaches the Odisha-Andhra coast.

Forecast analysis indicates that the system is likely to move from a relatively favourable low-shear environment over the south-central Bay into progressively hostile atmospheric conditions closer to the coast, where vertical wind shear could disrupt its vertical structure and put a ceiling on further strengthening.

That creates a significant distinction for Odisha's weather outlook: a strong rain-bearing system remains a serious possibility, while the probability of it becoming a severe, high-category cyclone appears constrained by the coastal atmospheric environment.

The forecast window under examination is broadly September 23–25, when the system is expected to approach the eastern coast.

Open Bay offers the system a launchpad

The initial phase is not the weak point of the forecast.

As the upper-air cyclonic circulation moves from Thailand towards the Andaman Sea around September 18–19, it is expected to encounter a low vertical wind-shear environment south of 15°N. Wind shear of around 5–10 knots is generally supportive of a tropical system because it allows the circulation to remain vertically aligned and helps convection wrap around the developing centre.

The analysis therefore indicates that the system should have an opportunity to consolidate over the southern and central Bay.

Ocean conditions add another layer of support. Sea-surface temperatures across the central and southern Bay are assessed at around 29–31°C, while the analysed marine heatwave covers a substantial part of the basin. Ocean heat content is also described as exceptionally high, exceeding 80–100 kJ/cm² in parts of the central Bay.

In simple terms, the system is unlikely to run short of oceanic fuel while it remains over open water.

The key question, therefore, is not whether the system can organise at sea. It is what happens when that organised circulation moves north-westward into a much less favourable atmospheric environment.

The coastal "shear wall" changes the equation

The forecast becomes substantially more complicated between September 21 and 24.

The central Bay is projected to contain a moderate-shear zone of roughly 10–20 knots, followed closer to the north-western Bay and coast by a much stronger shear environment exceeding 25 knots.

That transition matters.

Low shear allows a storm to build vertically. High shear, by contrast, can tilt the circulation, displace convection away from the low-level centre and prevent the core from consolidating efficiently.

The analysis identifies this high-shear zone along the immediate coastal sector of northern Odisha and adjoining areas as a potential atmospheric firewall. Strong upper-level easterly winds associated with the late-monsoon atmospheric pattern could interfere with the circulation just as it gets close to land.

This is where the system could face its biggest hiccup.

Why the models are not seeing the same cyclone

The divergence between the major models is itself important.

Model	Forecast treatment of wind shear	Broad implication
ECMWF	Assumes the circulation can partially shield itself through strong upper-level outflow	Deep Depression to marginal/possible Cyclonic Storm
NCMRWF ENS	Allows moderate shear to tilt and elongate the vortex	Depression/Deep Depression with broad circulation
INCOIS	Gives greater weight to the coastal high-shear environment dismantling the core	Weak/open circulation and no significant cyclone
NCICS diagnostics	Indicates strong tropical forcing and vigorous convection despite shear	Strong rain-producing system

The ECMWF scenario is therefore the more organised end of the forecast spectrum, showing a compact circulation and a large precipitation envelope extending towards the east coast.

The NCMRWF ensemble, however, points towards a broader and elongated depression rather than rapid intensification into a severe cyclone.

The INCOIS scenario is weaker still, with the coastal shear effectively dismantling the system's vertical organisation.

The common thread is not a severe cyclone. It is a moisture-rich system capable of producing substantial rainfall.

Odisha's bigger threat may come from rain, not wind

This distinction is crucial for interpreting the forecast.

The analysed system is expected to carry a large moisture envelope towards the Andhra-Odisha coast. Even if its circulation weakens or fails to achieve a high cyclone category, its rainfall-producing capacity may remain substantial.

The analysis indicates heavy to very heavy rainfall, broadly 7–20 cm, during September 23–25, with the coastal belt and adjoining districts particularly exposed.

Zone	Districts identified in the analysis	Possible weather concern
Coastal/Border belt	Ganjam, Puri, Jagatsinghpur, Kendrapara, Bhadrak, Balasore	Heavy rain, squally conditions and localised intense rainfall
Adjoining interior	Khurda, Cuttack, Jajpur, Gajapati, Rayagada	Prolonged rain, waterlogging, urban flooding and rapid stream rises
Northern/Western interior	Mayurbhanj, Keonjhar, Dhenkanal, Nayagarh	Rain spreading inland, with isolated flash-flood potential

For Bhubaneswar and Cuttack, the principal concern in such a scenario would consequently be rainfall accumulation and drainage stress rather than a destructive cyclone wind field.

September 23–25: The decisive phase

The next several days could therefore produce two very different weather stories.

Over the open Bay, the system has warm water, high ocean heat content and a favourable low-shear genesis zone. These ingredients can help it develop into a well-defined depression or deep depression.

But as it advances towards the Odisha-Andhra coast, the atmospheric equation changes sharply.

The ocean continues supplying energy, while the atmosphere increasingly works against organisation.

That is why the system could remain an efficient moisture carrier even if its wind structure deteriorates.

The present analysis consequently points towards a heavy-rainfall threat with a significant probability of intensity limitation near the coast, rather than a straightforward march towards a severe cyclone.

The final outcome will depend on how quickly the circulation strengthens over the central Bay, how long it remains over favourable waters, and – most importantly – how effectively its core withstands the sharp increase in vertical wind shear before reaching the coast.

For Odisha, therefore, the forecast message at this stage is relatively clear: do not equate cyclogenesis over the Bay with an inevitable severe cyclone landfall. The bigger and more persistent signal is for a moisture-loaded system capable of delivering heavy to very heavy rain, while coastal wind shear could become the critical brake on cyclone intensification.
Also Read: EXCLUSIVE| Cyclone Brewing: MME Consensus Points To Odisha Landfall On Sept 23–24; Rain Threat Bigger Than Wind