This year monsoon has started early in Nepal, probably because of global Climate warming up, rains afternoon and evening time, however trekking season also almost End, the monsoon climate effect Everest Base Camp Trek, Annapurna Base Camp, Ghorepani, Langtang region but still trekkers doing to Annapurna Circuit because this area is considered Rainshadow area.
Nepal has four seasons, June-August is monsoon season, September-November is the autumn season, and December-February is winter season, and March-May is spring season. The autumn and spring are the best Trekking season in Nepal Himalayas but in winter and monsoon season would not be suitable for Trekking except few trekking areas.
Many tourists visit Upper Mustang, upper Dolpo and Annapurna Circuit in monsoon season because in those trekking region very little rainfall. This trekking region called the rain shadow area even though small rainfalls compare to other trekking parts of Nepal.
Economically Annapurna Circuit is cheaper than Upper Dolpo and Upper Mustang because the permit cost is high for upper Mustang and Dolpo.
Click below link for more info: Monsoon Trekking Itinerary