When visiting Bali it is important to take the weather conditions under consideration. Although the Bali weather is understood to be sunny skies and cool breezes this is only half the tale. The weather in Bali isn't split into four seasons but rather into 2. There's the dry season and the wet season, with the temperature remaining pretty constant across the year. The averages temperature in Bali is 28C all year and even in winter you may expect it to fall to only 24C.
The hottest time to visit Bali is during the dry season which lasts from April to September, with June to September being the top season. There's very little rain at all during these months and you should expect to have 99% of the time you spend in Bali with sunny blue skies. There's slight rainfall in this time, but it is mostly in the afternoon, and although if can be a heavy downpour, only last a little while and then the sun comes out again.
The other, less popular season to visit Bali is during the wet season, typically from October to March, because of the very wet conditions. In this time of year you should expect awfully heavy rain for days if not for weeks at a time. It is this season that give Bali its dense tropical rain forests that it is known for. The high rain volume during the wet season gives the trees and plants lots of moisture to grow at an incredible rate.
In the entire year you should expect to have a high humidity which is at its peak during the stormy months and can reach as high as 90% which if you are not used to it can be very stifling. When coming to Bali and you are not used to living in a humid climate it is essential that you book a hotel that has air conditioning for you to acclimatize. The humidity is felt more inland where the coast gives way to a higher altitude and some areas are so dense with foliage that some folks can find it tricky to breathe.
The winds that blow in Bali are gentle to moderate and you don't get the major monsoons and gales that are associated with many Indonesian nations. There are some dazzling storms that are grand to experience, but apart from landslides there isn't any danger if you visit Bali in this time. Many people still come to Bali during this time as you will find that the Bali accommodation is less crowded and you will be able to find miles better rates.
With Bali being such a small island that is famous for its sea life and amazing scuba diving areas it doesn't really matter when you come to go to if you are interested by diving. Even during the heavy stormy season you are still guaranteed of some sunny days, it is just that when it rains it really rains and you may have to stay in the hotel during the heaviest of the downpours or spend some time doing some Bali shopping.