You need a (good) sub-editor.
I'm not especially good, but this is what I'd do with that storyline.
It was early September when the ocean went mad. The same day a family moved into the abandoned house behind the hill.
Cathy felt it rather than heard it, as she walked along the shoreline: a deep rumble as if from the depths of some mythical beast. Despite the calm air, a stampede of powerful breakers pummelled the sand until it almost vibrated.
Within seconds, The lifeguard sounded the alarm for swimmers to get out of the water.
Even as the alarm sounded, a bloodcurdling scream pierced the air. Cathy's head whipped round. Not 10m from the shoreline, a small boy's face twisted in terror. In the time it took for the scream to register, the boy had been dragged further out into the thundering swell.
Cathy rushed into the water and immediately knew something was wrong. She was a strong swimmer and loved to relax in the friendly ocean during the holidays. Today it was a ferocious beast, slamming into her body and pushing her downwards, sucking at her torso and thrusting her violently into the sand.
Above her efforts to fight the pounding, disorienting waves, she heard the boy's screams, she heard bare feet slapping against the sand and other would-be rescuers yelling instructions. And she heard the weirdest thing. Was that really the sound of dolphins trilling, squeaking, whistling? For one insane moment, she imagined dozens of great sea predators coming toward her. Whether to help or to kill, she could not tell.
She found her feet. Adding to her confusion, a silhouette appeared in the foaming surf. A boy about her age, sixteen, had positioned his hands close to his mouth. The most extraordinary squeaks and whistles were coming from the youth. No human, surely, could make sounds like that. "Can't you do something?" she appealed.
"I'm trying," he retorted, stepping closer to the angry waves. He had the most peculiar way of walking, as if he barely touched the sand. "Do you think they will hear me, in this maelstrom?"
Among the churning waves, the poor lad was trapped in a vortex. He was not waving. Surely he did not have long left.
Amid the confusion; the extraordinary young man beside her; the insanity of the ocean; she watched in terror as a waterspout grew from the waves and hurtled, with a deep, gut-wrenching roar toward the would-be rescuers on the sand.
In that moment, the lifeguard lost his cabin. Chunks of metal and wood flew from the vortex of the waterspout, causing the onlookers to flee. A metre-long bar torn from the stair rail buried itself in the flat sand, just centimetres from Cathy's leg.
Although the waves obscured all detail, Cathy saw dark shapes in the water. A dozen dorsal fins were targetting the whirlpool where the helpless young lad was being sucked under the waves.
Cathy knew; everyone in the beachside community know. Sharks go for the helpless. She wrenched the bar from the sand, no thought in her head but to smash it against the noses and plunge it into the murderous eyes of the swarming sharks.
Anger drove her forward. Anger helped her overcome the pounding, thrashing waves, with no thought except to deny the sharks their meal. Anger almost made her drive the stake into the brain of the nearest dolphin.
Wonder made her realise the sleek, powerful dolphins were supporting the drowning boy. Wonder as the pod worked intricately to bring the boy to shore. Wonder as it dawned in her exhausted brain that the strange lad on the shore had called them
There was a crazed look in the lifeguard's eyes as he stared into the ocean. Cathy followed his gaze. For a second, she couldn’t breathe or move. "You two." He looked from her to the strange youth with the extraordinary power to summon dolphins "Run! Inland! find high ground. Now!"
The mad water was running away from them, exposing sand, rocks, coral, kelp that had never before breathed air.
They ran, before anyone had time to yell, Tsunami!