Clouds are the key variable. When the sun shines on the ocean at a low angle of incidence, SW radiation enters the water and heats it. When it is cloudy, less heat enters the water.
So a critical factor in predicting changes to ocean heat content is being able to forecast clouds. If you can’t model clouds accurately, you can’t forecast changes in ocean heat content. If you can’t forecast changes in ocean heat content, you can’t forecast changes in climate. Period.
Climate models don’t model clouds accurately.