Source: The Library Of Congress Country Studies
Panama has a tropical climate. Temperatures are uniformly high- -as is the relative humidity--and there is little seasonal variation. Diurnal ranges are low; on a typical dry-season day in the capital city, the early morning minimum may be 24°C and the afternoon maximum 29°C. The temperature seldom exceeds 32°C for more than a short time.
Temperatures on the Pacific side of the isthmus are somewhat lower than on the Caribbean, and breezes tend to rise after dusk in most parts of the country. Temperatures are markedly cooler in the higher parts of the mountain ranges, and frosts occur in the Cordillera de Talamanca in western Panama.
Climatic regions are determined less on the basis of temperature than on rainfall, which varies regionally from less than 1.3 to more than 3 meters per year. Almost all of the rain falls during the rainy season, which is usually from April to December, but varies in length from seven to nine months. The cycle of rainfall is determined primarily by two factors: moisture from the Caribbean, which is transported by north and northeast winds prevailing during most of the year, and the continental divide, which acts as a rainshield for the Pacific lowlands. A third influence that is present during the late autumn is the southwest wind off the Pacific. This wind brings some precipitation to the Pacific lowlands, modified by the highlands of the Península de Azuero, which form a partial rainshield for much of central Panama. In general, rainfall is much heavier on the Caribbean than on the Pacific side of the continental divide. The annual average in Panama City is little more than half of that in Colón. Although rainy-season thunderstorms are common, the country is outside the hurricane track.
Data as of 1987