An analysis is made of very high resolution radiosonde data taken at seven western Pacific island stations during TOGA-COARE (Tropical Ocean--Global Atmosphere and Coupled Ocean-Atmosphere Response Experiment). Evidence is found for a wave near the tropopause with periods ~30--40 days and with very slow (~3 m s-1) eastward propagation. This oscillation appears quite coherent across the region considered (a 37¿ longitude spread). The oscillation has a short vertical wavelength (~3 km) and is strongly attenuated above the tropopause and thus would be very hard to observe in either satellite data or conventional meteorological analyses.