Answer:
The wind is fierce; it sounds like a locomotive.
Step-by-step explanation:
A semicolon is used to separate two independent clauses when there are no coordinating conjunctions to join them.
In this sentence, you have two independent clauses:
1. The wind is fierce.
2. It sounds like a locomotive.
Since there are no coordinating conjunctions between them, you have to use a semicolon after the first clause.