July 12 flight (surge genesis/moisture flux flight) This flight was called to investigate the possible genesis of a gulf surge. Surge genesis was likely because a well-marked mid tropospheric wave was propagating from the east across central Mexico and upper tropospheric difluence and upward motion was expected over the coastal plain of Sinaloa etc… A flight was called based on these forecasts, and the flight was not cancelled in the early AM of the 12th because widespread convection was observed in the early AM IR imagery. The flight was designed to cover some of the same legs flown on the first (moisture flux) flight, but would include additional legs over the southern Gulf to enhance measurements in the suspected genesis region. Porpoising was done throughout, but because the IOP soundings from surrounding raob sites were fairly frequent in time and dense in space the P-3 descended infrequently to 10K ft and concentrated on lower-level soundings. Main surprise was the strong southeast winds west of Mazatlan; these were associated with a strong early AM storm that passed through Mazatlan at 5 AM with very strong winds. However, SE winds were observed all along the Gulf, though much weaker to the north. Winds approaching 40 kts were measured in the central Gulf. A well-marked trough in the windfield was evident up to 800 mb, with NE flow above. The attached figures are self-explanatory.