The high seasons are July and August and the weeks surrounding Christmas and New Year's, when prices are higher and tourist traffic is considerably increased. Try to avoid these times as well as February and March (given the heat and humidity).
Climate -- Bali is just below the equator -- so days are a consistent 12 hours long -- and the temperatures always hover in the 80s Fahrenheit (upper 20s to low 30s Celsius). The rainy season lasts from October to April; rain usually comes in short, violent bursts that last an hour or so, and the humidity is at its crushing worst during this period. The hottest months are February, March, and April. Remember that it gets a bit nippy at night up in the mountains, but a light sweater will certainly be enough.
Public Holidays & Events -- Public holidays and events include New Year's Day (Jan 1), Idul Fitri (celebration of the end of Ramadan, in late Feb), Nyepi (a major purification ritual and a time when Balinese are supposed to sit at home, silent, in late Mar), Good Friday and Easter Sunday (late Mar/early Apr), Muslim New Year (mid-May), Indonesia Independence Day (Aug 17), Ascension Day of Mohammed (early Dec), and Christmas (Dec 25).
