Transport variations with periods of 3 ~ 5 days have been measured in the Korea (Tsushima) Strait by cross-strait cable voltage fluctuations and by direct, long-term measurement. Here we show that these variations can be explained in part by large-scale atmospheric pressure fluctuations over the East (Japan) Sea. First, using basin-wide averages of atmospheric pressure and sea surface height we show that sea surface height in the East Sea is not in isostatic equilibrium with atmospheric pressure, and that the imbalance is correlated with transport fluctuations. Second, we use a simple model to estimate the relationship between these quantities. The model displays a Helmholtz-like resonance in the observed range of periods and is in reasonable agreement with the observed transport variations.