First, the second part of your statements have to be written in the future. For instance: "... you won't be able to touch it", "...we won't be able to see", and "... because the [tide is coming in (or another reason)]". Secondly, to answer your question, we would use "getting" in the first two sentences in informal speech only. In written English, one would say "it is going to get hot/dark/wet ..." Edited to add: The third sentence is more complex. We would use: "is getting" more often than "will be getting". Here's an example: The shirt is getting wet because I dropped it into the lake. We wouldn't often use "getting wet" in the future, because it's not something that we can predict. One could say "It will get wet when it starts to rain". I hope this helps.

Yes "getting" is correct. "Becoming" however, isn't the correct form. You should be using "Become" instead. You could also say "it will get..." instead of "it will be getting" . Hope this helps.