The best month to go to Bali is September. The weather is perfect at this time of year, with the average temperature sitting at a comfortable 27 degrees Celsius. The sea is also calm and clear, making it ideal for swimming and surfing. If you're looking to avoid the crowds, then September is also a good time to visit as it's shoulder season. However, if you're after a party atmosphere then you may want to consider visiting during the peak season of June-August.