Scientists have identified several early signs that could help forecasters determine when a tropical cyclone is becoming organized enough to strengthen, potentially providing communities with more time to prepare for dangerous storms.
The new research is based on nearly three decades of observations collected by NOAA Hurricane Hunter aircraft.
It found that tropical cyclones generally need to become vertically aligned before they can significantly intensify.
Researchers describe the process in simple terms: a tropical cyclone needs to “stand up straight.”
A cyclone is a huge rotating system extending from near the ocean surface high into the atmosphere. Ideally, the centers of circulation at different heights are positioned roughly above one another.
But strong winds higher in the atmosphere can push the upper part of the storm away from its center near the surface, causing the storm to lean.
Meteorologists call this separation between the lower and middle parts of the storm “tilt.” One major cause is vertical wind shear, which occurs when winds change in speed or direction at different heights.
A strongly tilted storm usually struggles to intensify. But when its different levels become aligned, conditions can become much more favorable for strengthening.
Researchers from the University of Miami and NOAA identified four characteristics associated with storms that successfully straighten themselves.
These storms tend to have a strong, compact circulation close to the ocean surface. Their tilt is also positioned favorably in relation to the surrounding wind shear. In addition, they have stronger rising air and heavier rainfall close to the storm’s low-level center. Finally, they are more likely to be surrounded by favorable environmental conditions, including warm ocean water, plenty of moisture and relatively weak winds in the middle atmosphere.
The researchers discovered these patterns by analyzing the TC-RADAR database, which contains 1,510 radar analyses collected by NOAA Hurricane Hunter aircraft over 28 hurricane seasons between 1997 and 2024.
Importantly, storms that eventually became aligned were already showing noticeable differences about a day earlier.
They tended to have stronger and more tightly organized circulation near the surface, along with widespread, powerful thunderstorms close to the low-level center.
Those thunderstorms may be more than simply a sign that a storm is becoming organized. The researchers suggest that the strong upward movement of air inside them could actually help pull the tilted circulation into a more upright position.
The findings could be especially valuable for predicting rapid intensification, when a tropical cyclone becomes much stronger over a short period. Such changes can create serious problems because coastal communities may suddenly face a much more dangerous storm with limited time to prepare.
Hurricane Hunter aircraft can already measure many of the features identified in the study during routine missions, giving forecasters real-world information about whether a storm is becoming better organized.
The research could also help scientists test and improve computer models used to predict hurricane behavior.
Even recognizing the signs of strengthening one day earlier could be valuable, the researchers say, giving emergency managers and people in a storm’s path additional time to make evacuation decisions and prepare for potentially dangerous conditions.
