This is the 702nd most frequent French word.
fortes
"Fortes" means "strong" or "strong ones" (feminine plural).
Here, 'fortes' is used as an adjective agreeing in number and gender with 'pluies' (feminine plural), describing them as intense or heavy.
Les pluies fortes ont inondé les rues.
The heavy rains flooded the streets.
In this sentence, 'fortes' describes the subject 'elles' (feminine plural), indicating their strength or proficiency in a subject.
Elles sont fortes en mathématiques.
They are strong in mathematics.
The word 'fortes' is used here as an adjective to describe 'couleurs' (feminine plural), implying that the colors are bold or vibrant.