。
Tomorrow's weather will be sunny with occasional rain.
Literal
Tomorrow [possessive-の] weather [topic-は] sunny sometimes rain probably.
Typical Japanese weather-forecast phrasing. 晴れ時々雨 is a fixed news-style construction where 時々 ('sometimes/occasionally') links weather states without connectives — very compressed, almost telegraphic. でしょう here is the forecaster's hedged prediction, standard in weather reports. The noun predicate (weather state + でしょう) avoids needing a verb.