Season by season
Dry season (May–October)
The trekking season. Days are clear and nights on the rim are cold — close to freezing in July and August, which are also the busiest months on the trail. The savanna on the Sembalun side turns golden, and dust on the summit scree is at its worst. May, June and September have the best balance of stable weather and fewer tents.
Wet season (November–April)
Heavy rain, cloud, slippery paths and landslide risk. The park normally closes the trekking routes from around January to March, and the shoulder weeks either side can be wet. The waterfalls, by contrast, are thunderous and the forest is at its greenest; Tiu Kelep’s river crossing may be unsafe after downpours.
Sea conditions & crossings
You will reach the mountain by boat from the Gilis to Bangsal, a short crossing that runs in nearly all conditions. If your trip also depends on a fast boat from Bali, leave a buffer day between it and your trek start, especially between December and February.
Month by month
| Month | Avg high | Avg low | Rainfall | Crowds |
|---|---|---|---|---|
| January | 26°C | 18°C | 380 mm | Quiet |
| February | 26°C | 18°C | 340 mm | Quiet |
| March | 26°C | 18°C | 300 mm | Quiet |
| April | 27°C | 18°C | 180 mm | Busy |
| May | 27°C | 17°C | 110 mm | Busy |
| June | 26°C | 16°C | 60 mm | Busy |
| July | 26°C | 15°C | 40 mm | Very busy |
| August | 26°C | 15°C | 25 mm | Very busy |
| September | 27°C | 16°C | 55 mm | Busy |
| October | 27°C | 17°C | 160 mm | Busy |
| November | 27°C | 18°C | 280 mm | Quiet |
| December | 26°C | 18°C | 360 mm | Quiet |
Temperatures and rainfall are approximate long-term averages for the area, rounded; individual years vary and the islands themselves have no long-running weather station.
Festivals & events
- Trail opening (usually around April): the park announces the reopening date each year; the first weeks are green and uncrowded.
- Mulang Pekelem: a Balinese Hindu pilgrimage to Segara Anak, when offerings are cast into the lake; dates follow the Balinese calendar.
- Maulid Adat in Bayan: the Wetu Telu community celebrates the Prophet’s birthday with processions, music and ritual at the old mosque; the date moves each year.
- Rinjani 100: an international ultra-trail race held on the mountain in some years, usually in the dry season; trails are busier around it.
- Independence Day (17 August): Indonesian hiking groups climb to raise the flag on the summit — a spirited but very crowded date.
Our advice
Trek in May, June or September if you can. Avoid the week around 17 August unless you enjoy company. For the waterfalls alone, April and May combine strong flow with drier paths. Always confirm with your operator that the route you want is open before you pay. The region-wide picture is in when to go.
