‘There will be more low-pressure area days in post monsoon season of 2026’

When cyclone Arnab made a prolonged landfall along the coasts of Andhra Pradesh and Odisha on October 28, it appeared to be interacting with another low-pressure system to its northeast. But the India Meteorological Department (IMD) had not acknowledged the low-pressure system in its public bulletins.

What role did this overlooked system play in cyclone Arnab’s development? And what does the episode reveal about broader patterns of cyclogenesis over the Bay of Bengal, particularly during a year of very strong El Niño conditions?

In this interview, K J Ramesh, former director-general of the IMD, discusses these questions and the evolving dynamics of tropical weather systems over the North Indian Ocean.

Akshit Sangomla (AS): There was some confusion about the interaction between cyclone Arnab and a low-pressure area that made a secondary landfall along the coast of northern Andhra Pradesh and southern Odisha, a few hours after the cyclone Arnab's landfall. To what extent did this low-pressure event contribute to cyclone Arnab's intensity? Was the cyclone’s stalling on the morning of landfall also a consequence of this interaction?

K J Ramesh (KJR): At six-hourly intervals, between 00UTC [coordinated universal time] on October 28 and 00UTC on October 29, the presence of two distinct vortices was clearly visible at 700 hectopascal (hPa) level, at 00, 06,18UTC. The two-vortices gradually merged over a 24-hour period. During this critical phase of cyclone Arnab’s evolution, the system’s intensity and movement or landfall was stagnant for some time—until the full-scale merger was complete.

Meanwhile, during this 24-hour period, cyclone Arnab underwent rapid intensification before making full landfall on the afternoon of October 28.

Because of these unusual circulation characteristics of cyclone Arnab, heavy rainfall continued along the coastal Odisha and and over western interior Odisha, adjoining Chhattisgarh, from October 27 until October 29. Shown below is the estimated wind distribution, excluding gusts, at 3:40 am on October 28.

AS: There was also a substantial discrepancy between the peak sustained wind speeds of cyclone Arnab as reported by the India Meteorological Department or IMD (150-160 km/hour) and by the US Navy's Joint Typhoon Warning Center or JTWC (213-222 km/hour). These two agencies, as we understand, use different measurement techniques, but can those differences alone account for such large disparity?

KJR: The IMD operates a network of high wind-speed recorders along the Indian coastline, which enables it to record sustained wind speeds at three-minute averages. These observations provide most representative wind speeds associated with cyclone landfall.

On the other hand, JTWC assesses a cyclone, typhoon or Hurricane intensities and wind speed characteristics using satellites (Advanced Dvorak Technique) and the standard 34, 50, and 64-knot thresholdsfor wind radii criteria surrounding cyclone circulation (using scatterometry data). These estimates, however, are not equivalent to the actual, ground-based measurements done by IMD.

AS: ⁠There has been persistent convective activity over the Bay of Bengal during the post-monsoon season. How might the very strong El Niño in the Equatorial Pacific Ocean be influencing this activity?

KJR: Post monsoon seasons during El Niño years are usually characterised by above-normal rainfall activity. This pattern is evident during the ongoing October-December 2026 season, with Madden-Julian Oscillation (MJO) providing support currently. IMD’s extended range forecasts also point to sustained cyclogenesis [development or strengthening of a cyclonic circulation] potential over the Bay of Bengal over next four weeks.

In the coming weeks, both El Niño and the positive Indian Ocean Dipole (IOD+) phases are expected to approach their peak phases, and the basin-scale warming anomaly over the Indian Ocean up to the South China Sea are likely to play in favour of an above-normal low-pressure-area (LPA) days even in the post monsoon season of 2026. [MJO is an eastward moving weather disturbance that traverses the planet in the tropics and returns to its starting point in 30 to 90 days, on average. There can be multiple MJO events within a season]

AS: ⁠What is the general influence of El Niño on low-pressure systems and cyclone activity over the Bay of Bengal and the wider North Indian Ocean? Has this relationship changed over the past few decades?

KJR: The forecast of above-normal northeast monsoon rainfall during 2026 season over southern Andhra Pradesh, south-interior Karnataka, Tamil Nadu, Kerala, the Maldives and Sri Lanka indicates the possibility of above-normal LPA days. In general, a gradual increasing trend in northeast monsoon rainfall has been reported in a 2024 study by the Council on Energy, Environment and Water (CEEW), “Decoding India’s Changing Monsoon Patterns: A Tehsil-level Assessment”, based on Indian Monsoon Data Assimilation and Analysis (IMDAA) reanalysis data, as presented below.