Although the Gemara (Sukkah 29a) explains rain on Sukkos isn't such a great sign,
דתניא שפך לו רבו קיתון על פניו ואמר לו אי אפשי בשמושך - His master poured a jug of water on his face and said to him: I do not want your service.
are there any positive perspectives on having rain over Sukkos?
Right at the begining of Shaarei Teshuva 1,1 Rabeinu Yonah says:
מן הטובות אשר היטיב השם יתברך עם ברואיו, כי הכין להם הדרך לעלות מתוך פחת מעשיהם ולנוס מפח פשעיהם, לחשוך נפשם מני שחת ולהשיב מעליהם אפו, ולמדם והזהירם לשוב אליו כי יחטאו לו, לרוב טובו וישרו כי הוא ידע יצרם, שנאמר (תהלים כה, ח): "טוב וישר ה' על כן יורה חטאים בדרך"
From the bountiful good Hashem does for his creations, He shows them the path how to get up from their misdeeds and He taught them and explained to them how to prevent his Wrath from them and showed them to repent when they do sin with his Bountiful goodness as the Passuk states: "Good and straight is Hashem so He redirects sinners back onto the right path."
If we know that Hashem is upset its really a kindness to us to indicate that we need to improve ourselves, and He cares about us because otherwise we would sink and sin till no possible return like Pharoh when G-d hardened his heart (see Ramban Shemos 9,12)
