Hey Rahul, June is Monsoon time for whole of Maharashtra and Konkan. So if you don't mind the rains and minimal sunlight, you can go ahead and plan Tarkarli for June. I visited Tarkarli and Sindhudurg in Mid August, that was a pleasant time weather wise and also the non-peak season so added advantage.
Best time to visit Tarkarli.
October to March. Travelling here during the months between November and February is comfortable as the temperature is moderate. ...
July to September. These months are suitable for travelling only if you enjoy the monsoons as Tarkarli experiences heavy rainfall.