Mount Rinjani in December

April through October offers the most reliable weather, but each month brings trade-offs. May to September is peak season with clear skies and minimal rain, but also crowds and higher prices. July and August see the most trekkers, so book early. April and October are sweet spots — fewer people, decent weather, and shoulder-season pricing. The dry season doesn't mean zero rain though. Afternoon thunderstorms can roll in fast, especially during transitions between seasons. November through March is officially closed due to heavy rains and dangerous trail conditions, but some operators still run trips in November and March. Don't risk it — the trails become slippery death traps and visibility drops to zero. For summit attempts, plan to reach the crater rim during the dry season when you'll actually see something from the top. Cloud cover can persist for days during the wet season.