This is a common problem with wood located in sunny spots: the heat causes the wood to dry out too fast and shrink apart. There's no absolute fix for it. It's just an ongoing maintenance issue which you have to keep an eye out for.
There are other problems which crop up on shady spots, like mildew!
I cleaned the surface with a bleach-based cleanser before I repainted it. Then I scraped, patched and primed a few dozen other places where the paint was bubbling due to fluctuations in the weather.
Then I repainted everything and stepped back to take a look.
It looks great! And this summer, the weather has been ideal for sitting in the shade with a glass of lemonade and watching a parade. Or a motorcade. Or a serenade... a masquerade... a promenade by the fire brigade...
Anyway, if your porch or deck needs a little TLC, give me a call. I love this stuff!