The Kimberley has 2 seasons:
The Wet (November - April) & The Dry (May - October). The Wet is hot, humid, rainy and cyclonic.
The Dry is the ideal time to visit, with 30 degree days.
Both seasons are invariably hot, although the buildup weeks to the wet are kind of hotter.
April is a great time to see large volumes of water in the falls, while July and August is a great time to get more temperate weather, while still experiencing great fishing and wildlife spotting, especially as August is the Humpback whale migration period.
During the Wet, the Gibb River Road is alltogether closed and various areas can be flooded, keep that in mind while planning your trip.
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License.
Based on a work at Wikitravel.org & Traveldudes.org.