Characterizing the Weather Band Variability of the Texas Coastal Current

Current velocities from 21 years (1992-2012) of near-continuous observations are used to investigate the Texas Coastal Current on the western Texas-Louisiana continental shelf in the northwestern Gulf of Mexico. Observations were made using the moored current meters deployed as part of the Texas Automated Buoy System (TABS) and historical current meter data. The general coastal circulation is known to be deterministic, with downcoast flow (westward) in the non-summer months (September-May) and a reversal to upcoast (eastward) flow in the summertime (June-August). This study focuses on characterizing features of the Texas Coastal Current that include the onset, frequency, magnitude, and persistence of current reversals along with the upcoast transport that occurs during reversals. The determined interannual variability of the Texas Coastal Current is imperative for understanding the surface transport of water and mitigating associated coastal hazards, including oil, harmful algal blooms, and hypoxia.

Results show the onset of the upcoast reversal during the summer with a mostly downcoast flow during the non-summer at upper Texas coastal locations. More persistent currents are observed during the non-summer in the downcoast direction within the weather band frequencies (2-15 days). Currents with longer persistence are found to be relatively slow, generally below 10 cm s^(-1). Fast currents (> 50 cm s^(-1)) tend to be short-lived, typically lasting less than 72 hours. Maximum upcoast transport is observed along the upper coast during the summer, reaching a minimum in the winter and fall. A relationship between the along-shore wind stress and along-shore current velocity is indicated, signaling that the Texas Coastal Current is mostly wind-driven.

Spatial variability is present along the southern Texas coast. Current flow is directed downcoast during the summer and slightly downcoast during the non-summer at buoy J, the southernmost location. Currents near the coastal bend tend to be upcoast during the non-summer and slightly downcoast during the summer. Longer persistence is observed at the southern location in the downcoast direction during the summer, with several currents lasting longer than 15 days. Maximum upcoast transport is present during the winter along the southern Texas Coast, reaching a minimum during the summer. Some evidence of a relationship between the along-shore wind stress and along-shore current flow are present, indicating some wind-driven forcing on the current flow.

Less seasonal variability is present at offshore locations. Locations on the outer shelf display a general upcoast flow regardless of season. Longer persistence is observed in the upcoast direction on the outer shelf during the summer and non-summer. Maximum upcoast transport is present during the non-summer at all offshore locations. Little correlation is found between seasonal winds and along-shore current flow, meaning mesoscale features, such as Loop Current eddies, provide offshore current forcing.