adjective
DUBIOUS : The afternoon was very rainy.
GOOD : The afternoon was very wet.
DUBIOUS : It's rainy again today.
GOOD : It's wet again today.
GOOD : It's raining again today.
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When rainy is used it generally comes in front of words like day, afternoon, Sunday and season (NOT after a verb): 'The baby was born on a rainy Sunday in June.' 'When does the rainy season begin?'
The more usual word is wet: 'Apart from a couple of wet afternoons, the weather was fine.' 'If it's wet tomorrow, we'll go on Monday instead.'