Apparently the US knew that an attack was imminent. They knew the day before that war was very likely to break out because the Japanese embassy destroyed its files and encryption devices. In other words, the embassy basically put itself out of the embassy business.
The US high command told the Pacific commanders to prepare for an attack. The warning was specific enough for commanders to take action, and the time span involved was fairly specific. Not the precise day and hour, but certain a military should be able go on heightened alert for several days without giving itself a hernia. The commanders blew off the warning and nobody bothered to double-check that it was followed.
There was no suspicion that Pearl Harbor would be a target, however. The Japanese naval fleet was assumed to be safely in Japan. When they spotted the Japanese planes over the Pacific shortly before the attack it was assumed to be US planes' relocating, and nobody bothered to ask, "Hey, are those ours?"
I've read the August 2000 briefing. It was less specific by far than the warnings FDR and the US had for a military attack in 1942.
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