Dear Rabbi Simon.
During Sukkot we had rain in Israel. I was very happy about it, yet I was notified with raised eyebrows that my joy was misplaced, as this is likened to spitting in the face of my master, as the midrash (or Mishnah?) states. I then learned that it is the prevailing approach, as incompatible as it may be for the current water affairs in Israel. I could not find a reliable source for a discussion on this matter. However one person mentioned that he does recall a discussion regarding the type of rain on Sukkot. I hope you could refer me to that discussion and perhaps your own insight.
The Talmud (Sukkah 28b) likens rain on Sukkot to a servant who seeks to present a glass of wine to his master (which needs to be diluted with water), yet the latter spurns it, and throws the pitcher of water in his face. The analogy is that by forcing us from the Sukkah, Hashem is (ke-ilu) rejecting our efforts to fulfil the mitzvah of dwelling in the Sukkah during the hag. The basis for this is the assumption that rain at such an early stage of the season is not beneficial. However, since today that is not necessarily the case (from an agriculture and water table standpoint) IMO your joy need not be regarded as misplaced. Still, it would have been better if the rain had waited until after Shemini Atzeret.
Rabbi Rashi Simon