The continents have drifted together to form a new supercontinent - Pangaea ll. A single landmass like this creates a world of extreme climates. The single sea - the Global Ocean - has a huge anticlockwise current circulating around the southern hemisphere.
The rotation of the Earth has slowed, adding an hour to the day - now 25 hours. The sun is brighter, and temperatures have risen. Heating the ocean leads to frequent and very strong hurricanes.
The sea is whipped up by these frequent hypercanes. But the resulting rain does not travel far inland. It falls on a coastal mountain range.
The Rainshadow Desert is close to the huge peaks of this volcanic mountain range. The moisture rich clouds crossing the Earth rise over the mountains, losing water as they go and starving the land behind of moisture.
The hypercanes provide high humidity; they also supply food in the form of sea creatures whipped from the surface waters and dumped in the desert.