Cyclone Arnab became monstrous without warning: Is El Nino fuelling it?

Cyclone Arnab strengthened rapidly over the Bay of Bengal before becoming a very severe cyclonic storm. It developed a compact, tightly organised structure and approached Andhra Pradesh with destructive winds and heavy rain possible. The speed of its growth exposed limits in cyclone forecasting.

Arnab made landfall during the early hours of October 28, between 2 am and 4 am IST. Its outer spiral rainbands were already reaching land. The storm was also moving faster, which caused the expected landfall time to arrive sooner.

The exact weakening before landfall was uncertain. Interaction with land, ocean upwelling and changing winds could reduce its strength. However, even a weaker storm could still bring torrential rain, flooding, coastal inundation and damaging winds across Andhra Pradesh and inland areas.

A tropical cyclone intensifies rapidly when its circulation becomes much stronger in a short period. The process usually involves falling central pressure, faster sustained winds and a more organised storm core. It matters because communities and emergency planners may have far less time to prepare than forecasts initially suggest.

Arnab rapidly intensified over the Bay of Bengal into an exceptionally powerful and compact system. Its tightly wound inner circulation helped concentrate the strongest winds around a relatively small area. Warm water, moist air, strong thunderstorms and low vertical wind shear can all support this quick strengthening.

The article reports that several models failed to anticipate the extent of Arnab’s growth. Official estimates also appeared to underestimate its intensity until only hours before landfall. Satellite observations can track changes, but rapid shifts over open water remain difficult to predict.

Arnab’s published forecast identified it as a very severe cyclonic storm. Its sustained winds were estimated at 115–125 kmph, with gusts reaching 140 kmph. This classification describes the storm using India’s system, rather than the Saffir-Simpson scale used for Atlantic and eastern Pacific hurricanes.

A Category 4 hurricane has approximate winds of 200–250 kmph. The word “Drillbit” is not an official category. It informally describes a compact, tightly wound cyclone with a sharply defined core, like a rotating drill bit. Such a structure can concentrate destructive winds in a smaller area.

India’s classification also includes the higher category of super cyclonic storm. That designation requires sustained winds of at least 222 kmph. Therefore, the Category 4 label and India’s “very severe” classification should not be treated as direct equivalents.

El Niño is a recurring climate pattern involving unusually warm tropical Pacific waters. It can shift atmospheric circulation and influence weather far beyond the Pacific. The article links El Niño with warmer ocean waters around the broader system, suggesting that it may have added energy to Arnab’s development.

Warm seawater provides the basic fuel for a tropical cyclone. More heat encourages evaporation, loading the atmosphere with moisture. When that moist air rises and condenses into clouds, it releases latent heat. This heat strengthens the storm’s circulation, especially when winds are organised and the storm remains over water.

El Niño alone does not determine a cyclone’s strength. Arnab’s intensification also depended on wind shear, moisture, thunderstorms and its compact inner core. The article presents warmer water as a possible contributing factor, not a complete explanation for the storm’s sudden growth.

Rapid cyclone strengthening is difficult to forecast because several ingredients must change together. Forecasters must assess ocean heat, moisture, vertical wind shear and the storm’s inner circulation. Small or fast-moving changes can make a cyclone intensify much faster than earlier projections indicate.

Arnab’s compact core was especially important. A tightly organised inner circulation can allow winds to rise rapidly as pressure falls. Low vertical wind shear also helps keep thunderstorms near the centre, while warm water and moist air provide energy. These processes can reinforce one another over open water.

The article reports that several forecasting models failed to anticipate Arnab’s extent of strengthening. Official estimates appeared to underestimate its intensity until only hours before landfall. Satellites helped track the storm, but uncertainty remained because conditions and internal structure evolved quickly.

A cyclone usually weakens over land because friction increases and it loses direct access to warm ocean water. Ocean upwelling can also bring cooler water to the surface, removing some of the energy that powers the storm. Yet weakening describes a change in strength, not the end of danger.

Arnab could still produce destructive winds, torrential rainfall, coastal flooding and dangerous inundation after landfall. Heavy rain may trigger flash floods far inland. Strong winds can damage communities, while coastal waves and rising water threaten areas near the shore.

The article also notes that an eyewall replacement cycle could temporarily change Arnab’s wind structure and intensity. This means conditions may remain complicated even as the storm weakens. Emergency attention must therefore continue beyond landfall, especially along the storm’s path and in low-lying inland areas.

A tropical cyclone acts like a heat engine powered by warm seawater. Heat causes seawater to evaporate, adding moisture to the air above the ocean. This warm, moist air rises inside the storm’s thunderstorms. The process matters because it transfers ocean energy into the cyclone’s circulation.

As rising moist air cools, the water vapour condenses into clouds and rain. Condensation releases latent heat into the surrounding atmosphere. That released heat helps maintain rising air and lowers pressure near the storm’s centre. Air then flows inward, supporting stronger circulation and faster winds.

Arnab could intensify quickly because warm water, abundant moisture, strong thunderstorms and a compact core worked in favourable conditions. Low vertical wind shear also helped preserve its organisation. Forecasting remains difficult because these ocean and atmospheric ingredients can change rapidly over open water.