Yesterday was hot but it was (or "has been") said that today would be even hotter. However, it is much cooler as I myself feel even it is almost at noon now. ??? So, the weather forecast is not always right, not to say it is only right for about 70 percents. ??? I don't understand your second sentence. Could you explain it to me? What is the meaning of "feel"? Are you talking about how your body feels, or are you talking about how the time feels? I don't understand your third sentence. Could you explain it to me? What is the meaning of "not to say"?

Yesterday was hot but it is said that today would be even hotter. However, it is much cooler than I expected even though it's almost noon now. So, the weather forecast is not always right/accurate, not to say it is right only 70 percent of the time.