Here's why:
* Adverbs modify verbs, adjectives, or other adverbs. They tell us how, when, where, or to what extent something happens.
* In a sentence, "temporarily" will often answer the question "how long?" or "for how long?"
For example:
* The store is temporarily closed. ("Temporarily" modifies the verb "closed" and tells us how long the store is closed.)
* I am feeling temporarily better. ("Temporarily" modifies the adjective "better" and tells us how long the feeling will last.)