Question:
If a Ben Eretz Yisroel will be traveling to chu”l after starting to say vesain tal umatar, but before it is being said in chu”l, and will be returning back to EY before it is started in chu”l, what should be said while in chu”l?
Answer:
He should continue saying it while in chu”l, since you started saying it already and you are only going there temporarily.
Best wishes
Sources:
M:B 117-4, Halichos Shlomo ( Tefilla) 8-20, Eishei Yisroel 23-38.