It's difficult to give a general answer to this question because Maui is so diverse. But here are a few thoughts. In general, the rainy season runs from late November thru March. Often the rain is of the scattered showers type; but sometimes (rarely) one can experience days of steady rain.
It also depends on where in Maui you have in mind. It rains most in the mountains. In fact some of the wettest spots on the planet can be found in Maui where it rains nearly every day. No worries, though, since these rains occur where you would never go.
It rains more in the Hana area (but don't let this discourage you...Hana is super)!
On the west side, it rains more in Kapalua than in Kaanapali, but ditto above.
The weather is driest in the Wailea area.
Heat is not an issue. Summer is a great time to visit Maui. It almost never reaches 90 degrees F and humidity is nothing like southeastern US.
Cold isn't a big deal either. Nighttime temperatures rarely reach into the high 50's.
Trade winds can be an issue (especially in the summer) but they're delightful...and always come with good weather.