YOU SAID:

the weather is warming up this time of year

INTO JAPANESE

この時期は天気が暖まっています

BACK INTO ENGLISH

The weather is warm at this time

INTO JAPANESE

この時期の天気は暖かいです

BACK INTO ENGLISH

The weather at this time is warm

INTO JAPANESE

この時の天気は暖かいです

BACK INTO ENGLISH

The weather at this time is warm