Yes you could say "the temperature hit 30 degrees". (Include the article "the" to make it sound fluent.) There is a small difference between that and "the temperature was 30 degrees"... "was" is just a neutral statement about the temperature. Saying it "hit" a certain number means that it usually wouldn't be so hot, but this time it is unusual and it made it to that extra high number. Tim's comment is a good point, though... you should indicate C or F to mean Celcius or Fahrenheit if you're talking internationally.

By the way.... Of course I think you mean 30 Celcius which we wouldn't say in america. God I wish we used the metric system. So we would say "The temperature hit 86 degrees yesterday."

Yes we often say that in English when the temperature is at an extreme or it is unusual for a particular time of year.