Question

I (arrive) tomorrow,if the weather is fine

Answer 1

Hola mate the answer is
I will arrive tomorrow, if the weather is fine.

Answer 2

I will arrive tomorrow, if the weather is fine.

The verb will is representative of future tense.

Here the person is going to make a decision for tomorrow based on the weather condition.

He or she haven’t arrived yet and just foretelling what is going to happen if the weather stays fine.

In this situation the verb will complete the incorrect sentence.