According to the National Hurricane Center, rapid intensification is an increase in the maximum sustained winds of a tropical cyclone of at least 30 kt in a 24-h period.
Watch this video from the Pacific Northwest National Laboratory to learn more about this process.
Source: A Recipe for Rapid Hurricane Intensification | Pacific Northwest National Laboratory | YouTube
For a storm to intensify quickly, it needs to have these near-perfect conditions, which don't happen often. So, all of the environmental parameters that play a role in the intensification of the hurricane have to align themselves for this to happen. And that doesn't happen very frequently. For example, it can have a warm ocean surface, but at the same time, it could have a high wind shear, which doesn't allow the storm to develop. Or it could be the other way around. So, as the storm is moving westwards gradually, it begins to encounter these warm waters, which are typically there in the Caribbean Sea and the Gulf of Mexico. And when that happens, occasionally, it will also encounter low wind shear conditions, and when things align like that, then that would be like a perfect recipe for the storm to explode in strength.