The dry season from May to October is the best time to visit Lombok. This is when Mount Rinjani trekking is at its best (July–September are peak months), the surf is most consistent on the south coast, and the Gili Islands are at their most pleasant. The skies are clear and rain rare.
The wet season (November to April) brings afternoon rain, reduced visibility for diving, and the closure of the Rinjani summit route (officially closed February to March). The Gili Islands are still accessible and snorkelling is still possible, but diving conditions deteriorate. The upside: accommodation is cheaper, the islands are less crowded, and the green rice paddies of the interior are at their most photogenic.
The surf at Desert Point and other south coast breaks fires best in May to September when Indian Ocean swells are largest. For the Gilis, visibility peaks May to August in the calmer dry season. For Rinjani, start planning by April to secure guides for the July–September peak — groups book out months in advance.