Papa,
Congrats on 30 years! I agree with all of the above, but can maybe give you a little more insight.
End of November until mid of February is "rainy"season. Now understand Bonaire is an arrid island, so what we call rainy season are quick squalls of rain usually while you are sleeping. One or 2 days in the period you may get a day of rain, but no torrential downpowers for the whole day. It does make the vis go down to about 80 ft... not the normal 100+ vis...
Mid September-Mid October can be VERY hot. Our wonderful tradewinds usually decide to go on vacation, but the diving is GREAT. Excellent for coral spawning. Personally, I think anytime from March until Nov is the best for diving...
I also love August because I can watch the AMAZING meteor showers at night after a great day of diving. We used to watch them in the States when we lived there, but they are AMAZING in Bonaire.
Oh heck....there is NO bad time to come to Bonaire.....