Is there an opposite to the "Weather Boost"?
Solution 1:
Unlike the main series, where the weather may provide negative effects based on the Pokémon’s typing or lack there of, there are no hinderances with catching or battling based on the weather.
As far as I am aware, the only debuffs that currently exist in Pokémon Go are specific charge moves, like Close Combat, which reduces your stats in PvP.