Rapid intensification is when a storm increases in speed by 35 mph in just a day. That equates to going from Category 1 to a major Category 3 storm in a short period of time. Ida (2021), Dorian (2019) and Michael (2018) are just a few recent hurricanes that rapidly intensified. When that happens near land, it can catch people unprepared, and that gets dangerous fast.

Since rapid intensification can happen in a really short time span, we have to be out there with the hurricane hunters taking measurements while the storm is coming together.

So far, rapid intensification is hard to predict. We might start to see the ingredients quickly coming together: Is the ocean warm to a great depth? Is the atmosphere nice and juicy, with a lot of moisture around the storm? Are the winds favorable? We also look at the inner core: What does the structure of the storm look like, and is it starting to consolidate?

Satellites can offer forecasters a basic view, but we need to get our hurricane hunters into the storm itself to really pick the hurricane apart.

Hurricanes like to stand up straight – think of a spinning top. So, one thing we look for is alignment.

A storm that isn’t yet fully together might have low-level circulation, a few kilometers above the ocean, that isn’t lined up with its mid-level circulation 6 or 7 kilometers up. That isn’t a very healthy storm. But a few hours later, we might fly back into the storm and notice that the two centers are more lined up. That’s a sign that it could rapidly intensify.

We also look at the boundary layer, the area just above the ocean. Hurricanes breathe: They draw air in at low levels, the air rushes up at the eyewall, and then it vents out at the top of the storm and away from the center. That’s why we get those huge updrafts in the eyewall.

So we might watch our dropsonde or tail doppler radar data for how the winds are flowing at the boundary layer. Is that really moist air rushing in toward the center of the storm? If the boundary layer is deep, the storm can also take a bigger inhale.

We also look at the structure. A lot of times the storm looks healthy on satellite, but we’ll get in with the radar and the structure is sloppy or the eye may be filled with clouds, which tells us the storm isn’t quite ready to rapidly intensify. But, during that flight, we might start to see the structure change pretty quickly.

Air in, up and out – the breathing – is a great way to diagnose a storm. If that breathing looks healthy, it can be a good sign of an intensifying storm.

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