I haven't heard that early september was different than end of august. I think the bad bad times where start and end of the monsoon like end November and January-mid february
Hence, you should have mostly calm seas though not as flat as they can be from march to may. I've had quite some rain though, nothing that would strand you to your room, but the usual sunny morning, rain shower in the afternoon scheme.
from my experience, I would have stated :
March always sunny, flat seas, great viz 25m+ up to 30-35 sometimes, probably more!
August sun in the morning, calm seas, rain in the afternoon/evening, viz mostly like 15/18m up to 20-25m in the morning.
December, some rainy days but still no days without sunshine, quite calm seas, sometimes a little wavy, viz never up to 18/20m.