Unfortunately, the weather on the Carstensz Pyramid is unpredictable and often bad. The good news is that there is no “better” time in the year to plan your climb.
The weather is constantly changing at any time of the year and you should expect to be inundated with rainstorms, scorched by the sun, an even welcomed to the summit by an enthusiastic snowstorm.
To avoid the majority of precipitation, most tour companies plan their ascent days in the early morning, when the chance of rain and snow is much lower.
It should be noted that these chaotic conditions are only really seen in the highlands, where the mountain is located. If you plan to trek to Carstensz through the rainforest, however, it would be prudent to choose the dry season – from April to November.
At all times of the year, in the rainforests, you can expect temperatures of around 77F (25°C) in the day time, which drop to about 41F (5°C) at night.
Even in the relatively dry season, you should be prepared for warm afternoon downpours. As you approach the base of the mountain, the likelihood of afternoon snow increases, temperatures drop below freezing, and strong winds are a possibility.