When to visit Lombok depends of course on what you are planning to do there and not too much on the weather. The weather quite stable and it is not difficult to find the best time to visit Lombok.
But if you are going there for specific reasons or activities or festivals, then you might want to plan around it.
Lombok, in West Nusa Tenggara of Indonesia, share the major tropical climate of two seasons – the dry season and the wet season. It is also one of the drier places to enjoy in comparison to Bali or the other nearby counterparts with temperatures averaging around 30 C and are mostly humid.
Therefore mostly you may enjoy your time here with the good amount of sun if you can ignore the humidity, and during wet season with some bouts of rains in the day but it should not be much of a deterrence in your holiday.
The dry season is from May to October, where it is also the peak season where most tourists flock to Lombok, though this is also the best time to go here. The wet season is from October to March, with rain less than an hour a day, therefore can be your alternative choice to escape the crowd.
In terms of weather, the best time to go to Bali is from July to August as the temperature is at its coolest at these times and also the driest in terms of rain. But it is also the peak season naturally, thus take note of the tourist crowds and do book in advance.
However, it is still possible to travel in the rainy season. It may still rain during the dry season and not rain for a week in the wet season, and it usually comes down big but quick in the evening or late afternoons. Therefore if you must, traveling in Lombok during the wet seasons is still possible if you do most of your sightseeing in the morning and early afternoons and rest in the evenings.
High/Peak and Low Season in Bali
From April to September will be the high season in Lombok, as it is purportedly the dry season and also generally the summer holiday season in many parts of the world.
The quieter months are from October to March, and though it is considered the rainy seasons, most of the rains come only in the evening and leave pretty quickly. Therefore, it is still possible to enjoy Bali in this weather if you plan your days earlier and rest in the evening.
Best time to visit Bali
The best months to go to Lombok in terms of weather and also the crowd are the shoulder seasons, that is either March or October. At these times, you will have a relatively dry weather yet without the tourist crowds!
If you want to visit some of the festivals in Indonesia, the most interesting one in Lombok is the Bau Nyale Festival, normally in either February or March. Hundreds of people will rush to Lombok to catch a glimpse of the first nyale (worm-like fish) at this huge fishing festival.