An analysis of the number of thunderstorm days for the meteorological station at Juan Santamaria Airport and of days with storms in the 06-18 hour period for the other six synoptic stations of Costa Rica is made. On the Pacific watershed, it was found that the seasonal distributions of the number of days with storms in the 06-18 hour period are similar to the corresponding distributions of rainfall. This is because rain is produced mainly by diurnal convection. On the Caribbean watershed, this not occur in such a form, because it rains mainly during the night and the morning, With exception of Limón station (on the Caribbean watershed), the annual number of days with storms in the 06-18 hour period is in the 86-108 range. 1t was estimated, utilizing empirical relationships, that between 12.2% and 14.7% of the total number of lightning flashes go to ground. The máximum value for the total number of lightning flashes (intracloud and to ground) per km2 per month, considering the different meteorological stations and excluding the station of Limón, varies between 7 for Liberia to about 10 for Nicoya. The annual total s are between near 33 (Liberia) and near 52 (Nicoya). Excluding also Limón, the number of lightning discharges to ground per km2 per month varies between 0.96 for Puntarenas to 1.15 for Nicoya. The annual total s are between near 4.6 (Palmar Sur) and near 6.4 (Nicoya).
