Field measurements from the Central Equatorial Pacific Experiment (CEPEX) conducted from March 7 to April 5, 1993, are used to study the link between water vapor, convection, and sea surface temperature (SST) in a region of particular importance to global climate. The data are compared with results from a general circulation model (GCM). Three high-resolution simulations were carried out with slightly different initial conditions using European Centre for Medium Range Weather Forecasts (ECMWF) analyses from March 1, 1993, and forced with the observed SST as lower boundary condition. Radiosondes released between the equator and 5 ¿S show a dry region east of the dateline collocated with a clear sky region observed from the Japanese Geostationary Meteorological Satellite (GMS) in the first 2 weeks of CEPEX, which both vanish in the second 2 weeks. The model is able to reproduce this change in convective activity. Moreover, a comparison of the anomalies of the relative humidity profiles grouped according to SST and infrared brightness temperature (IRBT) indicates that the GCM correctly simulates the observed behavior. The atmosphere is relatively moist when the SST is warm and low IRBTs occur at the same time, that is, when convection takes place, and dryer than on average for the opposite case. In general, however, the model is too dry in the midtroposphere and too wet in the upper troposphere. Very good agreement is found between the simulated and observed ice water content, in particular with respect to its increase with in-cloud temperature. ¿ American Geophysical Union 1995