Sea surface inflow angle asymmetries show tropical cyclone movements

Despite extensive efforts in dynamic analysis, numerical modeling, ensemble forecasting, and machine learning having led to improved tropical cyclone (TC) movement forecasting over the last century, the fundamental physical mechanisms related to TC motion still lack direct observational evidence, constraining predictive understanding. In this paper, we propose that sea surface inflow angle asymmetries can reveal TC movement, and demonstrate this through a universal verification with 24 years of 34-kt wind radii (R34) data from the best-track archive and a high-resolution analysis of Super Typhoon Saola’s loop track. To assess the universality, we determine the sea surface inflow angle asymmetry from R34, which shows that nearly 60% of the results agree well with TC movement. Specifically, by analyzing five SAR (synthetic aperture radar) observations, we derived three distinct steering flows from the sea surface inflow angle asymmetries. These flows coherently explain the loop track movements of Super Typhoon Saola. Consequently, sea surface inflow angle asymmetries perform well in both universal application and specific cases, and we show that sea surface inflow angle asymmetries serve as a baseline for TC motion studies, while also incorporating dynamic factors such as wind shear, poleward pressure gradient force, and the Coriolis effect.