We honeymooned last August in Flic en Flac, on the west coast, staying in the Sugar Beach Resort.
The weather was lovely, at least 25oC throughout the day, but it did cool down in the evenings. That said, we ate outside each evening between 8.00 and 10.30pm, and i was more than comfortable in a short sleeved shirt.
Also, the sun sets on the west coast, so you get it for just a little bit longer.
We had a fantastic time.
Good luck...