Bali, 8 degrees south of the equator, is blessed with a tropical climate that's divided into two seasons. The dry season runs from April to September and most visit during this period although climate varies across the island. The length of this season is the reason why Bali has no malarial swamps. The rainy season, from October to April, generally sees a rain-shower every day. It can be humid, especially in the hottest months of January and February, but the rain doesn't tend to last very long and the ground steams dry as soon as the sun peeps out again.
Temperature varies across the island – the northern and eastern lowlands can be hot at about 33 Celsius (and it doesn't seem to get much cooler when the sun goes down), while the southern beaches tend to hover around a more digestible 26 degrees.
In Ubud in the centre, the temperature is moderated by its proximity to the central mountains and it can feel quite cool in the shade at 22 Celsius. The highland interior, which experiences year-round showers, is a good ten degrees lower than the coastal regions, and it can get to a cooler 18 degrees.