Where are you from. The weather in Negril is much like the midwest in the U.S. in the summer, hot and humid. When we get off the plane from St. Louis in June, MoBay feels like home almost. But the humidity in St. Louis is worse.
We were in Jamaica last June for my sister's wedding (not Couples, but a nearby resort because kids also attended...). The weather was nice - it was warm, but not terribly so and not as humid as I expected (it has been worse in Wisconsin!). I wouldn't hesitate traveling again to Jamaica during this time of the year. And expect a brief rain in the afternoon - not an issue and actually refreshing. Enjoy your trip.