Seasonal Upper Shelf Circulation Along the Central Western Gulf of Mexico: A Preferential Upcoast Flow Reinforced by the Recurrent Arrival of Loop Current Eddies

The shelf circulation along the central western Gulf of Mexico has been traditionally attributed to a local alongshore wind stress component (AWSC) that heads upcoast during spring‐summer and turns downcoast to reach long‐term monthly averages larger than ∼ 0.05 Pa during fall‐winter. Modern wind databases exhibit, however, a local seasonal downcoast AWSC more than 10 times weaker. A realistic numerical model implementation revealed that the effect of the downcoast AWSC is recurrently overwhelmed by the upcoast geostrophic shelf circulation induced by the anticyclonic Loop Current Eddies arrival. Sporadic energetic downcoast shelf flows were generated by erratic cyclonic eddies next to the shelf and by the propagation of coastally trapped waves; nonetheless, the upcoast AWSC and the recurrent presence of Loop Current Eddies induced a preferential upcoast shelf circulation throughout the year. The upcoast shelf flow reached long‐term bimonthly averages up to ∼ 50 cm/s during spring and summer. Although weaker, the shelf current remained preferentially upcoast during fall and winter with long‐term bimonthly averages less than ∼ 10 cm/s. The long‐term seasonal variability of the reproduced shelf dynamics represented the long‐term annual cycle of the directly observed local shelf circulation. Direct observations and a second numerical experiment revealed that the previously reported seasonal alongshore inversion of the central western Gulf of Mexico shelf circulation, with downcoast flows that reach long‐term monthly averages larger than ∼ 40 cm/s, can be attributed to both an exaggerated wind forcing during fall‐winter and an inadequate representation of the local mesoscale dynamics.