Eight years of data from the Tropical Rainfall Measuring Mission (TRMM) satellite, along with QuickScat winds, are used to analyze tropical instability waves (TIWs) and their influence on the overlying tropical atmosphere. TIWs are visible meridional undulations of sea-surface temperature (SST) fields on the northern and southern sides of the equatorial cold tongues in the Pacific and Atlantic Oceans that result from the dynamical instability of equatorial currents. They typically have wavelengths of about 1000 km and periods of 20 to 40 days. TIWs have a distinct seasonal cycle, and TIWs in Pacific Ocean also show a clear correlation with the ENSO cycle. Concurrent satellite observations of winds, atmospheric water vapor, cloud liquid water, and precipitation are used to demonstrate the influence of these waves on the atmosphere on daily and seasonal time scales.