We knew from intercepts that the Japanese fleet had sent a force with 4 Carriers to sea, and that it was to be refueled at sea after 8 days.
We watched for that fleet (no satellites then), and it did not come south, toward the Philippines. The only other way it could go was East, and the only target in that direction, that far, was Hawaii.
We also knew that all regular Japanese merchant shipping was ordered to be back in Japanese home waters by Dec. 4.
So that alone would have been enough.
It was the belief then that no airplane could survive the intense, concentrated anti-aircraft from several battleships (hence, Battleship Row was considered the best defensive posture against an air attack).
It was also the belief that torpedoes could not be used in an attack from planes in Pearl Harbor, because the harbor was too shallow.
Both beliefs were obviously wrong. (Hopefully we won’t pay that kind of price again for being overconfident and under-estimating our foes...)