Starting in 1997, and expanding in the year 2000, special pilot balloon observations have been made in Mexico as part of the Pan American Climate Studies Sounding Network (PACS-SONET). These observations, carried out by the Mexican Navy, have been made during the past 4 years at 6 sites along both Mexican coasts. Two of these sites fall within the Tier 1 domain of the planned North American Monsoon Experiment scheduled for the summer of 2004. These sites, located at the extreme north of the Gulf of California (Puerto Peņasco) and at Topolobampo, midway between the radiosonde sites of Empalme and Mazatlan, have provided additional information on the synoptic and diurnal variability of the low level flow along the Gulf. This presentation will describe the synoptic variability and mean flow at both sites during their period of record, as well as a comparison of the mean winds from these sites with the observations from nearby radiosonde sites.

In addition to the Gulf of California soundings, three other sites have operated around the Isthmus of Tehuantepec since 1997. These sites are useful in depicting the gap flow over the region and also the passage of tropical waves during the summer months. A description ("climatology") of the characteristics of the gap flow during summer and winter months will be shown, as well as the mean structure of tropical waves that pass over the region during July and August. The feasibility of detecting tropical waves from these observations will be discussed.