Twice a day, every day, the outgoing currents rip through Hol Chan. It's tidal and if you look up the rule of twelfths it explains slack water at the tides turn, when there is no current at all and then three to four hours later when the most water volume flows and current is at it's peak. High and low tides are widely published, so an indication of when the current is running is easily worked out. I see no reason why the Hol Chan Rangers can't have a flag system on the Ranger Boat indicating when the current is at it's peak.

Hol Chan current is also greatly affected by wind as when more water comes over the reef in large waves it has to exit back to sea somewhere and that is through the Cuts of which Hol Chan is the narrowest for miles. So on windy days it can be greatly magnified and is less predictable.

Generalising and not specifically talking on this tragic incident, if people were better informed of what to do if caught in a current a lot more people around the world would live through an incident like this. It is human nature to try and swim back where you came from and it is physically impossible for even an Olympic Swimmer, let alone an overweight out of shape average person to do this. It tires you out and you get into trouble very quickly. I speak from experience getting caught in a really bad Rip Tide in Northern Sumatra and was very lucky to survive as I did everything I possibly could have wrong.