It's not a common way of saying it perhaps, but you'd certainly understand it easily if someone said it. Also, I think if you had a "rather strongly" or "pretty strongly" then it'd be fine.
More importantly though, using it like this helps learn it, if the french term used is Strongly rather than Heavily - and Strongly is certainly the meaning of fortement, I would think.
Hello, Jason. It is only that "raining heavily" is the more natural expression rather than "heavily raining". Of course, grammatically they are equivalent. This course is for native English speakers so some expressions that may seem to be grammatically correct will not be incorporated.
I listened to this very carefully in bot the fast and slow pronunciations and still think that somehow there is an "r" in the second word, so my response was "il pleure fortement" How are we to distinguish between that and "il pleut fortement" (which was the the alternative I was considering)
I just submitted both the male and female voices to my French ears (with headphones) and couldn't hear an "r" in the second word.
Note that along with the presence and absence of "r", the « eu » is pronounced slightly differently for « pleure » (\plœʁ) and « pleut » (\plø), and a French native would definitely make the difference regardless of the presence or absence of a "r". Google translate has quite accurate pronunciation of them, although I can guess it is difficult to distinguish for a non-French ear.