The antonyms for the word "becoming sunny" would be any words that describe unfavorable weather conditions, such as cloudy, overcast, gloomy, stormy, rainy, or windy. These words denote situations where the sky is not clear or is obscured by clouds, cold winds, or precipitation. While "becoming sunny" implies a transition towards pleasant weather, its antonyms indicate the opposite - an impending or current period of unpleasant and potentially hazardous conditions. It is essential to be aware of these antonyms and to monitor weather forecasts to prepare for any adverse conditions that may occur.