Friends from Chutz LaAretz (where they will begin saying "Ten Tal U’matar only in December) will be visiting in Israel on 7 Cheshvan, when we begin saying "Ten Tal U’matar" here. Should they also begin saying it with us on 7 Cheshvan, or should they wait until December (by which time they will be back in Chuts LaAretz)? If they should begin saying it on 7 Cheshvan while in Israel, what should they do in a few weeks when they return to Chuts LaAretz where everyone else will not yet have begun saying it?
The Chida in his commentary to the Shulchan Aruch, Birkei Yosef, (Orach Chaim 117), says that they should start saying "Ten Tal U’matar" on 7 Cheshvan. This is also the opinion of the Mishna Br'ura (Orach Chaim 117:5). As far as continuing when they will be back in Chutz La'aretz, the opinion of the Chida is that they should continue so that it should not be a mockery. May Hashem grant us a blssed rainy winter.