Rain is one thing, because when it rains, it can and will do so anywhere on the Island of Roatan.
Winds and storm effects are quite different. The Northern approach takes a beating.
Any time during the Caribbean Tropical Storm Season (Aug>Nov), most all Hurricanes (and serious Tropical Depressions) track along a NW path... and well to the North of Roatan- usually no closer than 90 miles... and those are fairly rare. So- even when a close call swings past- a storm that is headed for Belize or Cozumel, the rain storms that spin-off of it can be pretty intense. These are usually accompanied by strong winds and wave, again~ affecting the North and West dive operations. A few of the better equipped dive-ops will move their boats to the South side.
Some people will mince words as to what constitutes the Tropical Storm Season, confusing it superficially with Hurricane Season. If rains and wind are what you are worried about, the effect can be felt almost anywhere in the Caribbean well into December. (and beyond... keep reading!)
The Bay Islands (and Coz & Belize) do absolutely share one common weather phenomena, the "Norther". Simply described, when you get a cold snap as far South as Texas, the weather will descend from the North and turn everything from Cozumel and South into puppy poop. The singular advantage that Roatan has over Coz and Belize is that it is 17 miles wide, so on the Southern "lee side", divers can still go merrily about their business, in the shadow of the blowing wind and waves.
Once things do calm down, a few days after any given blow, the North/West with greater water exchange, returns to its generally better 60~80' visibility, and the South side, being as sheltered as it is, retains the same 50~70' ranges. That is, for most experienced divers, an irrelevant factor as Northern diving is generally deeper with emphasis on larger creatures, whereas South side Roatan is shallower and focused on close range examination of tiny critters. Roatan and the Bay Islands are simply not noted for great visibility~ a fun sensation for sure, but again, of debatable value after you've experienced it once.
