Unfortunately, there seems to be a very likely scenario in which it will be raining tomorrow night, the first night of Sukkos. Beyond the disappointment of the impediment to fulfill the mitzvah at its first opportunity, rain on the first night raises a significant halachic issue. While this is in the Tishrei guide I distributed, I wanted to call attention to it since it's not a frequent occurrence.
Normally, when it rains, one is entirely exempt from eating in the Sukkah (and it is inappropriate to do so). However, on the first night of Sukkos, when there is a Torah-obligation for men to eat challah in the Sukkah, it is more complicated.
In theory, if there were a chance that the rain would subside within a reasonable amount of time, then one should wait to make kiddush/eat until the rain passes. With that said, it seems unlikely that the rain will stop during the night.
Therefore, kiddush and hamotzi should be done in the Sukkah without the bracha of leishev ba-sukkah. Eat a k'zayis (olive-worth) of challah in the Sukkah, and then the rest of the meal takes place inside.
(If the rain stops in the middle of the meal, then the meal should resume in the sukkah with the bracha of leishev basukkah. If the rain were to stop after the meal but before one goes to sleep, one should go out and eat a k'zayis of challah with leishev basukkah.)
If one has a tarp/awning to cover the schach, that can be applied on Shabbos and Yom Tov. However, it would be best to have it on the schach slightly open before Shabbos and Yom Tov.
