Today's flight investigated a strong mesoscale convective complex that formed in the early morning hours south of Mazatlan. The cluster of storms persisted into mid-afternoon, gradually shifting up the Gulf and inland. The P-3 took off under IFR conditions and ascended to the northeast, measuring 25 kt winds from the SE at 700mb. Thereafter, the P-3 flew generally west and south, then returned along the coast offshore from Puerto Vallarta. This part of the flight described the cyclonic flow associated with a lower-mid tropospheric trough (probably a component of the tropical farther south). Porpoising was between 500ft and 10,000ft. The P-3 returned over the Altair and flew north over the gulf to near Los Mochis, doing an E-W run across the Gulf in that area, before returning at 10,000ft to Mazatlan. In general, the flight was successful in capturing the synoptic environment of a major MCS complex over the lower Gulf and the subsequent surge-like feature.