The ocean is the planet's largest heat reservoir, storing solar energy for weeks, months and even years. Without this energy, tropical cyclones simply could not form. The upper layers of the ocean accumulate a large energy reserve known as ocean heat content. In the North Atlantic and the eastern North Pacific, September sees the highest number of hurricanes because the ocean has spent the summer storing vast amounts of solar energy. As this cycle repeats itself, the system grows stronger, much like an engine continuously fueled by the warm ocean.