Similan Liveaboard Diving Conditions in April-early May

[Ironborn]

I am considering the possibility of a liveaboard trip to the Similan Islands toward the end of the official season - April and possibly early May. I understand that the season ends in mid-May due to riskier weather conditions beginning at that time. I am curious as to whether or not that tail end of the season brings heightened risk of such unfavorable weather, e.g. has that specific and seasonal weather ever begun early, in April or early May, before the official end of the season? I noticed that some liveaboards stop operating earlier than others, even in mid-April, and was curious if that was because of risk of the seasonal unfavorable weather starting earlier than the official end of the season. Or, is the risk of unfavorable weather toward the end of the season just as high or low as it would be at any other point in the official liveaboard season? In other words, is the change in weather relatively sudden and predictable, or is it gradual and variable?

I also heard (please correct me if I am wrong) that visibility changes with the seasonal weather as well due to plankton blooms, and that those plankton blooms increase the chances of seeing large plankton feeders, such as whale sharks and manta rays. Is that correct? If so, what would it typically be like in April or early May?

 

[stevenl]

Chances of whalesharks and manta rays are highest around May, but there are sightings year round.

Most boats don't stop early due to unfavorable weather conditions, but due to less people around and having scheduled trips in other areas like Malaysia and Indonesia.

Chances of winds prohibiting a visit to Koh Tachai or Richelieu Rock are higher mid May than they are mid April.