"In summer I am sometimes here."
Translation:Néha nyáron itt vagyok.
The problem is we do not know the original emphasis of the sentence.
Néha nyáron itt vagyok. (Emphasis is "nyáron") Nyáron néha itt vagyok (Emphasis is "néha")
The question is, what is the core? "I am here in summer" and it is modified by "sometimes", or the other way, "I am here sometimes" and it is modified by "summer".
Your sentence, "itt nyáron néha vagyok" is weird because you separated the verb "vagyok" from "itt". I would not say it.