Nick Korniloff called the Jupiter Police Department at 4:23 p.m. Friday to alert them about his stepson Perry Cohen and his friend Austin Stephanos.
In a calm voice, the stepfather says the 14-year-old boys hadn't been heard from since about 11:30 a.m. and calls to a cellphone went unanswered.
"Usually he checks in and he's told to check in on a regular basis," Korniloff said.
The dispatcher says, "And you know we had a storm before, too?"
Korniloff says the boys went offshore, outside the bounds of their expected trip, though it's not clear how he knows this.
"We had no idea they were going offshore," he said.
The Coast Guard launched its search shortly after the 911 call was placed.
Meanwhile, the Coast Guard says its search for two missing teenage boaters will press forward at least into Friday.
Chief Petty Officer Ryan Doss says crews will continue surveying waters from Florida up through South Carolina throughout the day and overnight. A determination on plans for beyond that haven't been made, but Doss says there are no immediate plans to call the search off, since it is still believed there's a chance the 14-year-olds, Perry Cohen and Austin Stephanos, are still alive.
There are many unknowns about the boys, including whether they have life jackets on, might have a cooler or some other object to cling to, or have drinking water or food. The Coast Guard makes its decision erring on the side of best-case scenarios, while still noting there are limits to how long humans can survive in the open ocean.
The teens have been missing since leaving on a fishing boat on Friday.