"I'm glad that you brought an umbrella": If I want to mean something similar which is better, "It's good that you...." or "It's a good thing that you ..." or just "Good thing that you..."? 用 英語 (美國) 要怎麼說？

查看翻譯

The first one is correct.

How you can modify it is " It's a good thing that you brought an umbrella."

If you wanted to express gratitude you could add something to the line of " I'm glad that you thought a head." or " I'm glad we don't have to get rained on."
The "we" can be interchanged with "I" depending on if you are using the umbrella with another person.

"It's a good thing that you brought an umbrella. I'm glad we don't have to get rained on."

I hope this helps!