It i's humid today. It's humid today.

Yours is okay but this is another way to write it and still be considered proper English.

The temperature is about 25-celsius degree degrees Celsius and there i's no wind, so Iit feel hotts warmer than what it is. The temperature is about 25 degrees Celsius and there's no wind, so it feels warmer than what it is.

In the US, we usually put the unit after "degrees." Saying it's "hotter" instead of "warmer" is okay, too. We usually say, "it feels ..." in reference to the weather instead of "I feel ..."

However, I could see a rainbow this evening maybe thanks to this climateweather. However, I could see a rainbow this evening maybe thanks to this weather.

We usually use "weather" to describe how the weather is today and "climate" as the weather in a region from year to year. For example, "tropical" or "temperate" describe climates in different regions while "hot" or "cool" would describe how the weather is.