Magic continues to yield key pieces of the puzzle, but that info is not passed along, except in the most non specific terms to Kimmel in Hawaii.
Intel in DC has been tracking a series of “winds” messages from Tokyo to embassies, and receive a winds message that they, correctly, believe to be the war warning to the embassy, known as the “winds execute message”: “north wind clear”. Hawaii is never informed.
Kimmel, Navy Commander Hawaii, receives intel that the local Japanese consulate is destroying all but one code, and is burning documents, but fails to understand the significance of this.
The head of RCA, Sarnoff, had agreed to provide the Navy in Hawaii with the coded messages tapped from local Japanese and from the Japanese Consulate phones and messages. Key intercepts were provided on December 3, 4. Rochefort put his best people on it, but couldn't finalize decoding until Dec 10, at which point they realized they had the key info forecasting the attack.
How maddeningly frustrated and sick to their stomach they must have been on Dec 10.
The fact that they know that the Japanese are destroying their codes makes the infamous “winds” codes completely irrelevant. Perhaps redundant is a better word since both a “winds” broadcast and the knowledge of the destruction of codes mean the same thing. The fact that Kimmel and Short failed to understand the significance of this is really incredible when you think about it.