We have Hurricane Ana in Hawaii and have heavy rain all day……. I enjoyed a lazy day(LOL) When you watch the Japanese weather forecast, he/she often say “Ashita wa ame deshoo”. It means they are 70-80% sure. (It will probably be rain tomorrow.)When you predict something, you could use “desu or masu” ” deshoo” and ” kamoshiremasen”.

Ashita wa ame desu. (100% sure)
あしたは、雨　です。
Ashita wa ame deshoo. (70-80% sure)
あしたは、雨　でしょう。
Ashita wa ame kamoshiremasen. (50%sure)
あしたは、雨　かもしれません。