A numerical simulation of the Gulf of Mexico (GoM) using the Navy Coastal Ocean Model (NCOM) is used to identify the pathways by which fresh water discharged by major rivers in the northern Gulf is exported away from the region. The NCOM, a new primitive equation ocean model with a hybrid sigma/geopotential level vertical coordinate, is described along with its application to the GoM region. Trajectories from surface drifters are analyzed to show evidence of the seasonally shifting alongshore and cross‐shelf transport in the region. The model results are used to determine the preferred locations and times of year for cross‐shelf and along‐shelf export of low‐salinity water from the northern GoM. The annual cycle of local wind stress plays an important role in shifting the export pathway of the fresh water discharged from the major rivers (primarily the Mississippi River) toward the east in the spring/summer, where it can be transported offshore by the currents associated with deep ocean mesoscale eddies, and toward the west in the fall/winter, where it is transported southward along the Mexican coastline as a coastally trapped current.

The Loop Current and its shed eddies dominate the circulation and dynamics of the Gulf of Mexico (GoM) basin. Those eddies are strongly energetic and are the cause of intense currents that may penetrate several hundred meters deep. However, there are regions in the GoM and periods of time in which the local atmospheric forcing plays an important role in its dynamics and thermodynamics. The circulation on the shelves, and particularly on the inner shelf, is mainly wind-driven with seasonality, changing direction during the year with periods of favorable upwelling/downwelling conditions. The wind-driven circulation is associated with the transport of waters with different temperature and salinity characteristics from one region to another. The interannual variability of the circulation on the shelves is linked to the atmospheric variability. Intraseasonal variability of the wind patterns considerably affects the likelihood and magnitude of upwelling and downwelling. The geometry of the GoM is such that large-scale winds may drive opposing upcoast/downcoast currents along different parts of the curving coast, resulting in convergence or divergence zones. The width of the shelves in the GoM is variable;while the West Florida Shelf, the Texas-Louisiana shelf and the Campeche Bank are more than 200km wide, they are narrower near Veracruz and Tabasco. Another consequence of the GoM physiography and the wind forcing is the development of cross-shelf transports in the southern Bay of Campeche, the southern Texas shelf and southeast of the Mississippi river, which in turn vary during the year. During autumn-winter (from September to April), the GoM is affected by cold fronts coming from the northwest United States, which are associated with strong, dry, and cold winds that mix its waters and generate large sensible and latent heat fluxes from the ocean to the atmosphere. These frontal passages also cool the GoM surface waters due to mixing with lower temperature subsurface waters. During summer, tropical cyclones crossing the GoM can dramatically affect circulation and coastal upwelling

Eight cyclonic eddies were identified near the western edge of the Loop Current, at the northeast shelf break of the Campeche Bank, through TOPEX/Poseidon sea surface height anomaly data from January 1993 through March 2000. The eddies' migration and their lifecycle are described. The formation of the eddies appears to be related to the dynamics of the Loop Current because the timing of their generation corresponds to the last stage of the anticyclone shedding from the Loop Current. The cyclones intensify while moving slightly to the northwest along the shelf break of the Campeche Bank; later, some cyclones are observed to move northward toward the Mississippi shelf break. The cyclones remain next to the Campeche Bank, south of 268N, from 1.3 to 9.6 months; later, some of them move northward and strengthen by merging with other eddies, extending their life span. The eddies' vertical structure is analyzed with hydrographic data, and the connection between the formation of the cyclones and the evolution of the Loop Current is further described using sea surface temperature images.