Yes, morning visibility around the 6-7am time frame are very prone to fog. Usually both crew members will be CAT 2 qualified to be able to land in the lower visibility. On this particular day one of the crew was not qualified for the lower visibility hence the diversion to Haneda. I was actually concerned this morning coming in on my cargo flight for this very issue. My first officer had not yet been checked out for the lower visibility landings. Thankfully the visibility improved before our arrival at 7am.