Be sure to expresses an action which is almost certain to occur. The present tense therefore gives a future meaning:
Bruno and Horatio are sure to succeed. Bruno and Horatio are almost certainly going to succeed.
The weather is sure to be worse tomorrow. We can be certain that the weather will be worse tomorrow.
It was sure to happen! It was almost certainly going to happen!
• In imperative constructions, Be sure to... is a synonym of Make sure to, and has a similar meaning to Don't fail to...:
Be sure to bring your passport. Don't forget to bring your passport. It's important.
Make sure to arrive at the meeting on time. Do not be late for the meeting.
Don't fail to pay me back by Thursday. You must pay me back by Thursday.
• Be sure and Make sure can also be followed directly by a personal pronoun (you, she, they, etc), to express the same imperative sense:
Be sure she brings the report.
Make sure you wear pants to the meeting.