Enhanced water transport when a tropical storm meets an atmospheric cold front

Weather systems that interact with one another can enhance coastal water transport, facilitating the movement of waterborne materials. In this study, we examine the influence of such weather interactions on water transport within a tidal pass along the coast of the northern Gulf of Mexico, focusing on the event when Tropical Storm Lee (2011) made landfall and merged with an atmospheric cold front, which was a leading edge of an advancing continental polar air mass. We conducted continuous surveys using an unmanned surface craft to measure water transport through a tidal pass. The transport was analyzed by calculating a regression-based time series, with additional measurements obtained from a moored side-looking horizontal acoustic Doppler current profiler (HADCP). Our findings reveal that the combination of the tropical storm and cold front substantially enhanced the total water transport, driving significant amounts of water out of the bay. The storm tide-induced water transport through the narrow 500-m pass reached ~ 13,630 m³/s, with a maximum velocity around 2.4 m/s. The cold front amplified the effect of the tropical system by reinforcing winds and vorticity from both systems. Both weather systems contributed notably to the energy density in the sub-tidal band, while also overlapping the tidal and inter-tidal frequency bands. The sub-tidal-to-tidal-energy density (power) ratio increased from an average of 21-114% during the two weather systems and 205% during the tropical storm period alone. These results highlight the significant implications of such weather interactions for coastal erosion, sediment transportation, and sediment deposition during coastal weather events.