What determines the weather in the Haina Desert?

Question

Bulbapedia states that it is sunny during the day and has a Sandstorm at night, but that doesn't seem right at all, as it is currently daytime in-game and there's a Sandstorm (i am playing Ultra Moon, and it is a Sandstorm in both the regular and reverse world). I've always been curious about this and was wondering if anyone had a definitive answer.

Answer 1

What determines the weather? It's Time:

Harsh Sunlight times are listed below.

10:00 AM to 4:59 PM (Sun/Ultra Sun) or
10:00 PM to 4:59 AM (Moon/Ultra Moon)

Sandstorm times are listed below.

5:00 PM to 9:59 AM (Sun/Ultra Sun) or
5:00 AM to 9:59 PM (Moon/Ultra Moon)

The reason why you are experiencing the wrong weather condition could be that the Reverse World's time does not affect the weather from the main world.

Comments

This is the same info on Bulbapedia that asker has already seen, so you may need to explain more.