Ten days have already passedIts been ten days since autumn began, but it is still hot these days and the highest temperature can even reach. For example,the temperature can go anywhere from 36 to 40 degrees Celsius.

Instead, I only stay at home and turn on the air conditioner.

this can be included in the previous sentence.

I consulted thelooked at a 15 - day weather forecast, and it indicatedthey predict that the temperature won't dip until September.

predict/forecast = 预测

The temperature bBetween now and September, the temperature will still be between 36 and 40 degrees Celsius.

structural change.

Undoubtedly, I have to continue to endureing the heat for about anothermore ten days.

i have to continue (enduring) = 还有受苦

Ten days have already passed since autumn began, but it is still hot these days and the highest temperature can even reach up to 36 to 40 degrees Celsius.

Your original sentence was good, I just suggested this alternative which still conveys the same idea.

I can't go out during the daytime.

Your original sentence was still good, I just prefer how “during the day” sounds (but I think that’s purely personal preference)

I consulthecked the 15 - day weather forecast, and it indicated that the temperature won't dip until September.

Depends on the context - “consulted” feels very formal to me