Bromo Tengger Semeru in May

April through September offers the clearest skies and least rain. July and August get crowded with domestic tourists, but the weather is most reliable. May and June hit the sweet spot - good visibility without peak season crowds. September can be excellent too, though afternoon clouds build more frequently. Avoid October through March if possible. The wet season brings daily downpours, and clouds often obscure the mountains entirely. But if you do come during rainy season, aim for early morning before the weather deteriorates. For Semeru climbs, stick to dry season. The summit is often cloud-covered during wet months, and river crossings become dangerous.