Last year I went to Valley of Flowers & Hemkund trek during monsoon (Aug). There was forecast of heavy rains which was a risk factor in mountains and i was wary of it. But thankfully there were light showers here and there and the trek experience was absolute amazing and fulfilling. The light showers were good enough to keep the weather pleasant and cool, usually due to heavy rains people have to turn back from valley of flowers but in my case due to pleasant weather i was able to go till the last allowed trekkable point in valley of flowers.