Are these three 'stormy' sentences synonyms?
Solution 1:
All the phrases (preferable 1st and 2nd) can be interchanged for colloquial usage, yet there are subtle differences.
- A storm coming means it is right about the happen. On your doorstep.
- A storm approaching to an extent can be understood as less urgent.
- A storm brewing implies it has not yet acquired its shape/intensity.
All of them are natural depending on the context. I am more of a laid back person so I prefer "a storm coming" (when I finally take note of it).