Three Decades of Radar Data Reveal Signs a Hurricane Is About to Strengthen

A tropical cyclone can look powerful from above yet still struggle to intensify if its circulation is leaning through the atmosphere rather than stacked vertically. Scientists at the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science and NOAA's Atlantic Oceanographic and Meteorological Laboratory have identified four features that indicate when such a tilted storm is about to straighten up and become capable of rapid intensification, using nearly three decades of NOAA Hurricane Hunter aircraft observations.

"A tropical cyclone has to stand up straight before it can intensify," said lead author Michael S. Fischer, an assistant professor in the Rosenstiel School's Department of Atmospheric Sciences. "Strong winds higher in the atmosphere can push the top of a storm's circulation away from the center near the ocean surface. Until those centers come back together, the storm usually cannot intensify substantially." Meteorologists call this horizontal separation between a storm's lower- and middle-level circulation centers its "tilt," and vertical wind shear can push those centers further apart.

The four features that favored a storm becoming vertically aligned were a compact circulation close to the ocean surface, a tilt oriented favorably relative to wind shear, stronger rising air and heavier rainfall near the low-level center, and an environment with warm ocean water, plentiful atmospheric moisture and relatively weak midlevel winds. The researchers drew on TC-RADAR, a database of 1,510 radar analyses from 28 hurricane seasons between 1997 and 2024. "The storms that aligned already looked different about a day beforehand," Fischer said. "They had stronger, more tightly wound circulations near the surface and more widespread, vigorous thunderstorms lifting air near that center."

Because reconnaissance aircraft can measure most of these features during operational missions, the findings could help forecasters spot disorganized storms that are becoming more capable of strengthening, and could also be used to check whether high-resolution hurricane models correctly reproduce the alignment process. "Even a modest increase in forecast confidence a day earlier can provide more usable preparation time for communities in a storm's path," Fischer said. The study, published in the Journal of Geophysical Research: Atmospheres, was supported by the National Science Foundation.