[Grammar] I hope that the weather is/will be fine tomorrow.

[wotcha]

1. I hope that the weather is fine.

2. I hope that the weather will be fine.

3. I hope that the weather is fine tomorrow.

4. I hope that the weather will be fine tomorrow.


I think 1 and 2 can be used interchangeably. \

Then how 3 and 4?

 

[Raymott]

1. I hope that the weather is fine.

2. I hope that the weather will be fine.

3. I hope that the weather is fine tomorrow.

4. I hope that the weather will be fine tomorrow.


I think 1 and 2 can be used interchangeably. \

Then how 3 and 4?

1 and 2 can't be used interchangeably in all situations. 3 and 4 probably can.
The problem with 1 and 2 is that you haven't stipulated whether you mean now or some other time.