Florida Current meanders and gyre formation in the southern Straits of Florida

Abstract

Moored current measurements, shipboard hydrography, and a time sequence of satellite‐derived surface thermal images are used to show the formation and evolution of cold, cyclonic gyres coupled to large offshore meanders of the Florida Current in the southern Straits of Florida (SSF). Gyre formation is dependent upon the orientation of the Loop Current as it enters the SSF. With a well‐developed Loop Current the flow overshoots the entry to the SSF causing the formation of a cold recirculation off the Dry Tortugas, approximately 200 km in size, that persists over timescales of about 100 days. The demise of the gyre occurs as it moves to the east at about 5 km d−1, reducing to half its original size off Big Pine and Marathon Keys and unobservable off the northern Keys. Previously observed local gyres between Key West and Islamorada, Florida (Lee et al., 1992), are identified as a latter stage in the downstream evolution of the gyres formed off the Tortugas. When the Loop Current is not developed, flow from the Yucatan Channel turns anticyclonically into the SSF, causing strong eastward flow over the slope off the Dry Tortugas and lower Florida Keys, and gyre formation does not occur.