Rewrite the following sentence so that related ideas are expressed in similar or parallel structures.
Weather forecasters predicted a hurricane, and emergency plans were developed by local authorities.
Please explain your steps and process.
This is a compound sentence, and the first clause is cast in active voice ('forecasters predicted') while the second clause is in passive voice ('plans were developed by').
This sentence is fine as it is, but if one wished to make the clauses parallel, one would have to cast both in active voice:
Weather forecasters predicted a hurricane, and local authorities developed emergency plans.
OR both in passive voice:
A hurricane was predicted by weather forecasters, and emergency plans were developed by local authorities.
As you should be able to see, both of these latter sentences are less interestingly composed than the original, which demonstrates that parallel structure is not always the best style.