2 of us are heading to Thailand for full month of August. Looking for best bang for our buck on the Liveaboard. Was hoping to go on the Junk but it's out of commission. We're not loaded but want to see what's the best available.
The "green-rainy-SW monsoon-low" season on the Andaman Sea side of Thailand is actually quite a nice time to dive the Andaman Sea despite what you may read and hear from so many other (non-West Coast) people on this board.
True, there are days with rain, wind and rough seas but I would say there are MANY more days with fine weather, great visibility and calm seas. Also, dive boats and dive sites tend to be quite a bit less crowded than during the "hot-dry-NE monsoon-high" season.
Just to give you a little example: yesterday at Racha Yai Island we had 35+ meter visibility, sunny weather and calm seas. Those conditions are quite rare to get even in the "high" season. Last Friday there was a whaleshark at Homerun Reef on Racha Yai, the week before that one on the King Cruiser Wreck and a couple of days before that 2 whalesharks at Phi-Phi Island. Unfortunately because of poor information and/or misunderstandings it is still believed by many divers that we only see whalesharks during March-April and only in the Similan Islands and at Richelieu Rock. (Actually already since the year 2000 whaleshark sightings are NOT all that common anymore at Richelieu Rock)
The Similans are CLOSED for diving between May and October but there are still a few liveaboards operating in the Phuket/Phi-Phi/Koh Lanta area that you could join. The Junk is this rainy season in Bangkok on a movie project but boats like Sai Mai, Sea King and others still run cruises throughout the "wet" season.
Even on a "bad" diving day (poor vis, current, rough) I believe the diving is more interesting and colorful on the Andaman side than on the Gulf of Thailand side. That said; I must also admit that I have done plenty of great dives at especially Sail Rock and Chumpon Pinnacles in the Gulf.
I recommend you to go to the Andaman Sea and to do your dive holiday from Phuket. August is a fine month for diving and you will have a great time.