Genesis of the Gulf Stream Subseasonal Variability in the Florida Straits

The properties and generation mechanisms of the Florida Current on the subseasonal timescale (20-100 days) are evaluated from in-situ and satellite observations. The Florida Current volume transport estimates from submarine cable measurements reveal that subseasonal variability accounts for 37% of the total transport variance and is most variable from September to November. Here we show that coastal-trapped waves are the primary driver of the subseasonal variability in the Florida Current transport. The role of local winds and open ocean signals is of secondary importance. The alongshore wind component of the anomalous North Atlantic subtropical anticyclone generates the subseasonal coastal-trapped waves off the northern South Atlantic Bight coast. The subseasonal coastal-trapped waves propagate from Cape May to Apalachicola, behaving as Kelvin waves in the Florida Straits and as continental shelf waves along the rest of the waveguide. They affect the Florida Current transport by up to 2.6 Sv, on average. As the subseasonal waves propagate into the Gulf of Mexico, their energy substantially dissipates. The wave amplitude at Port Canaveral of up to 15 cm is three times higher than at Apalachicola. Concurrent subseasonal changes of the meridional overturning circulation in the subtropical North Atlantic are discussed.