。
Get up early tomorrow morning.
Literal
Tomorrow [possessive-の] morning [topic-は] early get-up [assertive-よ].
起きろ is the plain imperative form of 起きる — the gruffest command form in Japanese. Softened slightly by the final よ, which makes it feel like a reminder or assertion rather than a pure bark. This is the kind of thing a parent or older sibling would say.