How pre- and post-monsoon information can shape cyclone preparedness in the Bay of Bengal

Tropical cyclones (or hurricanes) are intense storms often featuring high winds, heavy rain and the potential for a lot of damage. Despite the wealth of information on cyclone impacts themselves, there has not been much learned about the impacts cyclones have on oceanic stability and recovery. The Bay of Bengal (BoB) is a hotspot for such activity, leading researchers to look into how the pre-monsoon and post-monsoon seasons might shape the frequency and tenacity of tropical cyclones in this area. A team of researchers compared pre-monsoon and post-monsoon tropical cyclones of the same categories using the same key markers to find significant differences in oceanic conditions between the two seasons. The information found highlights the importance of seasonality in cyclone intensity and the ocean’s response pertaining not only to the Bay of Bengal but also to areas with similar conditions.

Researchers published their results in Ocean-Land-Atmosphere Research in August 2025.

“The Bay of Bengal responds differently to pre-monsoon and post-monsoon cyclones, creating unique seasonal patterns in sea surface temperature, salinity, mixed layer depth, and biological productivity,” said first author and scientific officer Siraj Uddin Md Babar Chowdhury.

Results demonstrated the importance of seasonality on cyclone conditions by measuring multiple factors during the pre-monsoon season (March to May) and post-monsoon season (October to December). Understanding these differences is paramount to the goal of predicting cyclone impacts.

For example, the sea surface temperature (SST) during the pre-monsoon season ranges from 29°C to 31°C, whereas for the post-monsoon season, there is less variability (28-29°C), indicating pre-monsoon cyclones might be more influenced by the higher ocean surface temperature and post-monsoon cyclones by the ocean’s structure.

Additionally, post-monsoon sea surface salinity (SSS) information indicates post-monsoon cyclones could be more driven by rainfall than the pre-monsoon cyclones, which appear to be primarily driven by drastic changes in salinity due to more freshwater availability. Sea level pressure (SLP) also appears to indicate stronger winds and lower pressures of a cyclone system in the post-monsoon season.

However, not all of these factors can instantly be measured. There is a time delay for some of the upper ocean responses, making ocean monitoring during the pre- and post-monsoon seasons critical for improving prediction accuracy. Some distinct differences between pre- and post-monsoon seasons have been observed, such as higher sea surface temperatures and coastal freshening (a noticeable decrease in the salinity of the water near the coast) seen in pre-monsoon cyclones, and cooler surface water temperatures and elevated chlorophyll-a (the predominant type of photosynthetic pigment found in algae) levels in the water for post-monsoon cyclones.

Even though there are some limitations to the study, such as the limited sample size and short time frame in which the comparative analysis was done, there is still promising information from which future plans can be built. Researchers hope to utilize high-resolution models and real-time ocean observations to continue their analyses and predictions on cyclone-driven ocean changes. Expanding upon the observations already made, the goal is to develop early warning tools and forecasts to protect regions that are vulnerable to cyclone damage and impacts, as well as inform adaptive mitigation strategies for damage that is inevitable when dealing with such forces of nature.

Siraj Uddin Md Babar Chowdhury of the Physical and Space Oceanography Division at the Bangladesh Oceanographic Research Institute, Md Minarul Hoque of the Bangladesh Oceanographic Research Institute, Showmitra Chowdhury of the Biological Oceanography Division at the Bangladesh Oceanographic Research Institute, Anik Karmakar, Md Enamul Hoque and Tabassum Hossain Tahsin of the Department of Oceanography at the University of Chittagong contributed to this research.

No specific funding was received for this research.