Average climate for these nations is influenced heavily by the presence of warm ocean waters which maintain high temperatures and high humidity. The influence of the ocean waters also maintain fairly constant climate throughout the year, and so these nations tend not to experience seasons as we do at higher latitudes. Most notable here are the small daily and annual ranges of temperature.
Tropical climates result from general circulation of the atmosphere.
When air comes in contact with the tropical ocean it becomes high in temperature and humidity, and sees little change over long horizontal distances. The dry tropics, which lie in the eastern and polewind ends of the tropical oceans result from large scale sinking of the Hadley-Walker circulations. Rainfall is these areas can fall well below 100 centimeters per year. Some countries which are considered to be in the dry tropics are the line Islands in the Pacific. In some nations, half of the yearly rainfall can occur within 10 percent of the time, while most days within this region are usually fair, with few clouds.