I'm sweating like a pig. It's a sauna in here. I'm dying from the heat. I'm melting. Kushushu namhlanje - it's hot today (Xhosa)

There are many things you could say! Here are a few more examples (US English): It's extremely/incredibly/unbearably/super hot today. I can't believe how hot it is. I'm sweating buckets. I'm sweating like a pig. I can't stand/bear/tolerate this heat. This heat is too much for me. etc.

Another option for you. We often use the word "scorcher," especially if the sun is intense that day. So you can say : It's a scorcher today/ It's gonna(going to) be a scorcher today/tomorrow. Note that "gonna" is informal and very common in conversation. But it's best not use it for formal writing like reports or job applications etc.

Instead of “it is”, just say “it’s” (sounds more natural 🤗) “It’s so hot out” is very common. 🫶🏼