The Diurnal Cycle of East Pacific Convection, Moisture, and CYGNSS Wind Speed and Fluxes.

The far eastern tropical Pacific is one of the rainiest locations on Earth. This region is characterized by a robust diurnal cycle with precipitation initiating over the Andes mountains in Colombia in the late afternoon and moving offshore overnight while organizing into mesoscale convective systems (MCSs). As the MCSs move westward, they can seed tropical easterly waves that develop into tropical cyclones. Novel measurements of near‐surface wind speeds and latent heat flux (LHFLX) from the Cyclone Global Navigation Satellite System (CYGNSS) mission and ERA5 reanalysis are used to evaluate changes to regional flow patterns, moisture, and LHFLX that favor a strong westward propagating diurnal cycle of precipitation in this region. Days with strongly versus weakly westward propagating diurnal precipitation are compared during the extended boreal summer of the CYGNSS era (May–October 2018–2021). Strongly propagating days have a more moist lower troposphere with stronger vertically integrated moisture flux convergence than days with weakly propagating precipitation. The enhanced low‐level moisture is supported by increased wind‐driven LHFLX from stronger regional flows including the Choco and Caribbean Low‐Level Jets and Panama and Papagayo gap winds. Increased offshore convergence and vorticity also help sustain convection during the days with strongly propagating precipitation. Background variations in the physical environment, as opposed to diurnal variations, seem more important for supporting a robust diurnal cycle of precipitation in the region. Plain Language Summary: The eastern tropical Pacific Ocean off the coast of Colombia is one of the rainiest locations on Earth. Thunderstorms frequently form in the late afternoon over the foothills of the Andes mountains and then move offshore into the eastern Pacific overnight and into the early morning while growing into bigger thunderstorms. These large thunderstorms are important because they can eventually lead to tropical cyclone development as they move westward over the eastern Pacific parallel to central America. We evaluate environmental conditions that favor days when thunderstorms move far away from the Colombian coast along central America versus days when thunderstorms stay closer to the Colombian coast. We find that days when the thunderstorms move farther away from the Colombian coast have more moisture near the Earth's surface. This enhanced moisture is supported by increased winds near the surface in the east Pacific and Caribbean that help transport moisture from areas near the Pacific equator and Caribbean to offshore of Colombia and transfer moisture from the far eastern Pacific Ocean surface into the overlying atmosphere. Measurements from eight microwave‐size satellites in space were critical to determine the role of the transfer of moisture from the ocean surface to the atmosphere. Key Points: An index is developed to distinguish between days with strong versus weak westward‐propagating diurnal precipitation in the far east PacificStrongly propagating days have increased low‐level moisture, regional circulations, and gap winds relative to weakly propagating daysCyclone Global Navigation Satellite System measurements show that increased moisture on the strongly propagating days is supported by increased wind‐induced latent heat fluxes [ABSTRACT FROM AUTHOR]