Move effect that does double damage in a certain weather?

I want to make a move called Tropical Wave that does double damage in Sunny weather. How would I make the move effect for that?

Try getting the move effect of Solar Beam (because changes with sun) and the effect of Venoshock, that doubles damage when poisoned. Just see the if condition of Solar Beam and put it into Venoshock.

I'm pretty sure weather ball doubles in power for any weather except sandstorm. It also changes type depending on the weather, so you'll have to take that bit out but otherwise it would be a good template to start with.