Why is it unusual for Uncle Henrik to say “Tomorrow will be a good day for fishing” in Lois Lowry's Number the Stars?

The quote which you are asking about comes in chapter eight of Number the Stars. The reason that Uncle Henrik’s comment “Tomorrow will be a day for fishing” is strange is because Uncle Henrik was a fisherman, and fisherman didn’t wait for good days to fish. Uncle Henrik goes fishing every day, rain or shine.
When Uncle Henrik says this phrase, it strikes Annemarie as odd, and she makes the connection with something she’d heard her father say on the phone. He’d asked Uncle Henrik if the weather was good for fishing. This was their code to determine whether it was a good time to bring Jewish people to Sweden. Uncle Henrik goes on to talk in code about their plans, which include a funeral for a great-aunt that Annemarie is pretty sure they don’t have.