Tropical Cyclone Patterns Near Sri Lanka and Their Environmental Controls: A 45-Year Analysis (1980–2024)

Tropical cyclones (TCs) are infrequent but potentially high-impact hazards for Sri Lanka. Using IBTrACS best-track data and ERA5 reanalysis for 1980–2024, a Sri Lanka-centered climatology was developed to characterize storms approaching the island and the large-scale environmental conditions associated with their occurrence. Storms were identified using proximity thresholds within a 700 km screening domain; 67 TCs satisfied the ≤100 km direct-impact criterion, corresponding to approximately 1.5 events yr −1 . Sri Lanka-influencing tracks were dominated by Bay of Bengal systems propagating westward to west-northwestward at low latitudes. Peak-intensity timing near Sri Lanka was strongly seasonal, with a primary maximum in October–December and a secondary peak in May, consistent with the broader bimodal seasonality of North Indian Ocean TC activity. Storm-event rainfall over Sri Lanka, accumulated within a fixed ±48 h window centered on closest approach, showed substantial overlap between direct-impact storms and near-miss storms, defined here as systems whose minimum center-to-coast distance was >100 km and ≤300 km. This result indicates that offshore storms can still produce notable rainfall over land even when their centers remain away from the coast. Trend analysis indicated no statistically significant long-term change in direct-impact frequency or genesis location over 1980–2024. Wavelet analysis further suggested that variability in annual direct-impact counts is weighted more strongly toward interannual than lower-frequency timescales, although no robust long-period oscillation is inferred because of the short record length and edge effects. Environmental changes were selective rather than uniform: storm-peak deep-layer shear increased significantly; OND mean SST and RH700 also increased significantly, whereas OND lower-tropospheric wind extremes, low-level vorticity, and upper-level divergence showed no significant long-term trends. Overall, the results show that near-miss storms remain rainfall-relevant for Sri Lanka and provide a Sri Lanka-focused hazard climatology linking storm proximity, rainfall-footprint relevance, and environmental conditions.