Bali is always warm, humid and tropical, remaining around 30C to 35C all year round. The April-October dry season and November-March rainy seasons are only relative, with plenty of rainfall around the year, but the Balinese winter is cloudier, more humid and with a higher chance of thunderstorms.
A more important consideration is the tourist season, as Bali can get packed in July-August and again around Christmas and New Year's. Australians also visit during school holidays in early April, late June and late September, while Indonesians visit during national holidays. Outside these peaks, Bali can be surprisingly quiet and good discounts on accommodation are often available.