Seguro que mañana hará buen tiempo.


#1

i’m sure tomorrow will be good weather


#2

I cannot comment on the validity of the translation; however, the “I” is always capitalized when referring to first person pronoun. Also, it seems more natural in English to say “Tomorrow the weather will be good.” To avoid ambiguity in the Spanish sentence where “tiempo” could mean time or weather, one might use the word “clima”.