Scientists Explain Why Cyclone Arnab Paused off Andhra Coast

Visakhapatnam: The very severe cyclonic storm, Arnab, remained almost stationary over the west-central Bay of Bengal for several hours on October 28, an unusual behaviour that experts attribute to the interaction of multiple weather systems in the region.

According to Dr KSR Murthy, a retired scientist at the National Institute of Oceanography, “contending atmospheric forces likely caused the cyclone's prolonged stationary phase and disrupted its normal forward movement toward the AP coast.”

Murthy said, "Generally, this happens when the track of a cyclone is resisted by opposing forces."

He explained that strong westerly winds, a developing low-pressure area over the Bay of Bengal, and another cyclonic system forming near Myanmar may have collectively influenced Arnab's movement, slowing it down and even restricting its advance.

IMD recorded the unusual situation on October 28, reporting that Arnab was "practically stationary" over the west-central Bay of Bengal near latitude 16.4°N and longitude 82.0°E. The cyclone was located about 30km east of Narsapur, 45km south-southwest of Yanam, and 70km south-southwest of Kakinada while maintaining its severe intensity.

Despite its restrained movement, Arnab continued to pack power with sustained winds of 115-125kmph, the gusts reaching up to 140kmph. IMD noted that landfall occurred even as the cyclone remained nearly motionless for several hours.

Meteorologists say while a cyclone generates its own internal circulation, larger atmospheric steering currents majorly govern its movement. When surrounding weather systems exert opposing influences, these steering flows can weaken or become disrupted, causing a cyclone to slow down, alter its track, or temporarily stall.

In cyclone Arnab's case, Dr Murthy believes strong westerlies, a developing low-pressure system over the Bay of Bengal, and cyclonic circulation near Myanmar created a complex atmospheric environment.

"The complex weather systems prevailing in the Bay of Bengal are responsible for slowing down or keeping Arnab stationary," he observed.

However, he cautioned that only detailed meteorological analysis can determine the precise role of each atmospheric feature.

For coastal communities, a cyclone's speed can be as important as its intensity. Even without strengthening, a slow-moving or stationary cyclone can prolong heavy rainfall, strong winds, and storm surge over the same area, increasing the risk of flooding, coastal inundation, and infrastructure damage.

Arnab's pause highlighted the challenges of cyclone forecasting, wherein not only wind speeds and landfall location but also a storm's forward velocity play a critical role in disaster preparedness and response planning.

The episode reminds us that a cyclone's behaviour is shaped not only by its own dynamics but also by the wider atmospheric systems around it, which can sometimes produce unexpected and potentially hazardous changes in movement.