Characterizing Tropical Easterly Waves across Central America during the Organization of Tropical East Pacific Convection (OTREC) Experiment

Abstract The Organization of Tropical East Pacific Convection (OTREC) experiment took place from 5 August to 9 October 2019 in Costa Rica, with additional measurements collected in July and August of 2022. To observe the interaction of tropical easterly waves (TEWs) with the diurnal cycle over Central America and to assess the wave vertical structure over land, we installed a network of 15 global positioning system receivers with meteorological packages (GPS-Met), as well as two radiosonde sites, from the Caribbean to the Pacific coast. An outgoing longwave radiation (OLR)-based wave index indicates that 13 TEWs passed over the surface network during OTREC, with an additional 15 waves during 2022. The relative phasing of peak GPS column precipitable water vapor (PWV) with peak rainfall, together with vertical velocity and moisture profiles of wave active phases from reanalyses, suggests that isolated convective systems with lower-tropospheric heating and moisture evolve into more organized convective systems with elevated heating and moistening as the wave’s active phase progresses inland over Costa Rica. The signatures of propagation in rainfall, PWV, and cloud-top temperature are most pronounced for the active phase, with rain events observed to propagate westward across the network with about a 12-h lag from coast to coast. In contrast, local diurnal land–sea-breeze interactions with strong surface heating play an important role in the timing of convection during the suppressed phase. Significance Statement The results of this study shed light on how tropical easterly waves, westward-propagating disturbances observed over tropical latitudes, interact with the diurnal cycle in rainfall, land–sea-breeze circulations, and low- and midlevel easterly winds over Central America, enhancing the frequency and amount of rainfall and modulating its timing over the region. These results not only highlight the importance of scale interactions in rainfall processes for tropical land areas with strong oceanic influences but also provide situational awareness to operational forecasters tasked with predicting local-scale impacts of synoptic weather events.