Everyone talks up the tropics, but how many of you have actually flown there?
Most of the build ups (as J3 said) are in the afternoon. They are generally coastal and scattered. If you have a GPS and divert around them you will not have a problem whatever time of day you fly. If a storm happens to be over the airstrip you are landing at, hold. It will be gone fairly quickly.
The main problem you will experience is flooding of unsealed airstrips and the risk of a prop strike in mud or getting bogged.
If you plan to land at sealed strips only, you will not have a problem. If you get stuck in the weather there are plenty of airstrips around to put her down and wait it out.
I would suggest doing a flight through the topend in the wet. It will give you 'wet season experience' and it is the most beautiful time to fly. The air is crystal clear (no smoke,haze, dust) everything is bright green, there is water everywhere, and the waterfalls are in full swing in all the national parks.
Take a camera, you will get some photos of some amazing weather, most of which you can appreciate from a distance and make sure you post it on here!
GG