Virtually all previous work on the subject of atmospheric normal modes has concentrated on the relatively long-period Rossby modes, such as the familiar ''5-day'' and ''16-day'' waves. However, theory does predict the existence of shorter-period Rossby-gravity, Kelvin, and gravity modes. In the present investigation, long time series of hourly and 3-hourly barometric observations from several tropical stations were employed in a search for these high-frequency modes. Evidence was found for several spectral peaks that can be identified with various Rossby-gravity, Kelvin, and gravity wave normal modes. Particularly prominent is the zonal wave number 1 Kelvin normal mode with a period of about 33 hours. This mode was found to undergo systematic seasonal and interannual variations. The theory of short-period normal modes in the Martian atmosphere is also briefly examined. Such modes might be detectable in the surface pressure time series obtained in the Viking missions to Mars.