Well, I've never yet failed to see Drew's truck up there so he's probably got the place wired.
Yes, at Shark's Cove, if you get near or outside of the MLCD line -- just about the 50ft contour -- on rare occasions there can be a fairly strong longshore current pushing toward Waimea Bay. That's one reason that nearly all ocean contests go from Sunset to Waimea. Gauging the wind and looking at the water can give a clue. If the wind direction and current are more or less the same direction and close in speed, the water will tend to look smoother. If wind and current are opposing, the chop will be more pronounced; the wave peaks will be steeper. Within the MLCD, there's typically a slight clockwise circulation. In summer, it rarely can be noticeable but not a problem. To find the direction of a current, you can obviously watch your drift. But also, the "mu" (bigeye emperor) fish is also known to habitually face into the current. (Makapuu, Waimea Bay, and Makaha tend to go clockwise also.)
Tide charts can be used two ways. The first is obvious to check the local tidal flows. The second is to check for north-south (latitude dependent) currents by comparing the tide times at different areas of the island. For example, I believe the tides at Haleiwa are about an hour ahead of Honolulu. Since water runs "downhill", if for example, Haleiwa has a high tide before Honolulu, then you can expect some kind of current moving north to south until Honolulu catches up. This is part of the explanation for the confusing reports of the "Molokai Express" along the east coastline switching directions (Usually, the tradewind-driven currents dominate, but on still or southerly wind days, the Molokai Express toward Molokai can be quite strong.)
At Haunauma, there's a counterclockwise current in the swimming area. Basically, the surf on the left or "backdoor" side of the Bay typically comes in higher than on the right. This means more water coming into the left side of the swimming area. This water flows to the right, along the beach, and exits through the cable channel. If like most people, you only look at the surf at the cable channel, you may get the false impression that the current isn't too bad. But you must also look left and check the surf breaking over the reef to the left. If it's big, there could be a potent current at the cable channel. Waves tend to come in sets of about 5, maybe about 10-15 minutes apart. So don't just look for a few minutes and say "good to go". (Experienced big wave surfers typically will sit on the beach for an hour and often more, just studying the wave patterns. The yahoos tend to just jump right in; all balls and no forehead.)
The same idea also applies to the entry/exit at Kahe Beach Park but is more obvious. The volume of surf breaking over the shelf on the park side is an indication of how much water will be exiting through the swimming channel. Trying to exit by puliing in underwater might not be a good idea if it's big because you'll probably be driven into the very shallow bottom by the breaking waves. It might be better to bodysurf in, taking great care to not let your legs get flipped overhead, somersaulting you. Also, your navigation has to spot-on to avoid getting face-planted and rolled on the shelf on the right (on the park side) and eating the boulders to the left (on the cooling pool side).
The Waianae coast is notorious for a strong offshore current from Kaena towards Honolulu. This seems to connected with surf and the tide differentials. When they line-up, it can be a ripper. This is most noticable at about the 40ft gradient which is fairly far offshore except around Mt Lahilahi where deepwater is relatively close in.
A dive that was supposed to be "easy" left me pretty shaken.
