I don't know if the content at the first link below is visible to everyone or just to subscribers (?) because some of their content is public but not all, but Undercurrent offers a nice, succinct "seasonal dive planner" that summarizes seasonal conditions for many destinations, from A to Z:
Seasonal Dive Planner - Undercurrent
They also offer a destination guide with dive and vacation information about many popular destinations, resorts, dive ops, and liveaboards, the Caribbean page at the link below is available to everyone but it links to more detailed "whole world" content for subscribers:
Caribbean Diving Guides for Dive Resorts & Liveaboards
After perusing the info on SB and UC I think that
Aruba may be a good option for you,
@rmssetc, and your wife. I have never been there and I know that it is not considered a top dive destination but it is popular with some divers. The seasonal information and destination description for Aruba on Undercurrent and SB sounds like it might be a nice compromise for you and your wife in August.
It won't have diving like Cozumel - but it doesn't sound like you will melt from the heat and humidity, either - or be driven crazy by the biting insects - or be chased by storms. It should be easy to get there and the water is warm. Also, it is below the hurricane belt - which is a nice feature in August!
Here is an excellent, recent report about Aruba as a dive and vacation destination posted by
@2airishuman and it sounds like it would work well for you. The dive op that he used was even called "Mermaid" so it could be a sign that this is the place you are looking for!
Trip report: Aruba
Also see the Undercurrent descriptions below:
"Aruba
With no more than three degrees °F difference between summer and winter air temperature averages and low annual rainfall, the main factor affecting diving in Aruba is the wind. The trade winds blow year-round but are highest from January through April. Bad weather on the coast of Venezuela can also cause a decrease in water visibility.
Diving Aruba Overview
Near the Venezuela coast, the Dutch-owned island of Aruba has diving that doesn't match neighboring sister islands, Bonaire and Curacao, but some operators will take you to a few decent sites. Miles of white sand, glitzy casinos, hotels, and restaurants may make it a good compromise destination for the nondiving spouse. There are several good boat dives. The South Wall, past San Nicholas near the southern tip of Aruba, is also good. Aruba lies south of the hurricane belt."
I believe that the reader report below for Aruba is publically available; it is from December 2017; but the author has dived widely in many parts of the world and has made several trips to Aruba, in fact she did two trips there in 2017. She says that there are easy, non-stop flights from East Coast cities available and that the water temps vary from 82 to 83 Fahrenheit.
Here is a comment from her report:
"...Aruba isn't Bonaire, but you will see most of the same kinds of fish and plenty to do topside... I paid $352 including CC charge (3%) for 10 dives with my own equipment. That's 4 or five dives in Hawaii. BTW, Aruba is ALWAYS windy; keeps the bugs away."
https://www.undercurrent.org/members/UCnow/dive_reviews/Aruba/SEArubaFlynDive_report_10084.html