The best time to go to Koh Phi Phi is from December to April. From May the monsoon sprinkles the island regularly with torrential downpours. September is particularly a bad moment to go to Phi Phi islands, it is the rainiest month. It is also better to not com in October.
We are one week away from Chinese New Year (January 25th, 2020) and despite a lot of mail and detailed information requests from various Tourist Offices in several cities, I unfortunately did not get all the details that I would have liked...