In the western Gulf of Mexico, depth contours of the 15 ¿C isotherm are compared during two observation periods: April 1--12 and April 12--26, 1978. Comparison of the two isothermal maps allows one to estimate changes in the mesoscale current patterns. A cyclonic circulation feature and an anticyclonic feature are found in both data sets and seem to have intensified and weakened respectively. Two possible causal mechanisms are discussed. The observed changes may be due to the effects of a severe norther (cold air outbreak) that occurred between the observation periods. An alternate mechanism is the dissipation of energy associated with the spindown of a westward moving anticyclone as it reaches the western boundary of the Gulf of Mexico.