July to September and we are firmly in the Kingdom of Bhutan's monsoon season, with the heaviest rains occurring in the west, which includes the nation's capital, Thimphu. In July the daily highs are around 25 °C, but it is muggy and average precipitation in the capital reaches 373 mm monthly. Thunder and lightning often comes before the rain, with large dark clouds plunging the skies into a frequent overcast gray. Travelers duck between the showers and head inside to visit significant historical and religious sights dotted throughout central Bhutan, such as the Changangkha Temple in the Thimphu valley, or the Watchtower of Trongsa Museum, which offers unrivalled insight into the nation's political history.
In northern Bhutan, though precipitation depends on altitude and is much lower than in other regions, it is significant enough to make many of the trekking routes too wet and muddy for safe passage, with many choosing to wait for the drier autumn. The temperature remains fairly constant in the highest alpine areas along the Tibetan border, remaining between 4 and 8 °C both day and night, though it is up to 10 degrees warmer at lower elevations. While not ideal for trekking, the higher altitude flowers come out over the summer months, and it is a good time to seek out a sheltered vantage point to watch the mountain meadows as they slowly burst into summer bloom.
The climate in southern Bhutan is hot and humid ranging from 15 to 35 degree Celsius throughout the year. Virtually any time of the years is good to visit though the summer monsoons bring the natural limitations of the constant downpours.