Hurricane Hunters Identify Four Key Indicators of Storm Intensification

Scientists have identified four critical features that signal when a disorganized tropical cyclone is transitioning into a vertically aligned structure capable of rapid intensification. The findings, derived from nearly three decades of data collected by NOAA Hurricane Hunter aircraft, were led by researchers at the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science in collaboration with NOAA’s Atlantic Oceanographic and Meteorological Laboratory.

Tropical cyclones require vertical organization to grow stronger, meaning the rotating centers of the storm at different atmospheric levels must stack directly above one another rather than remain tilted. According to Michael S. Fischer, an assistant professor at the Rosenstiel School and the study’s lead author, strong upper-level winds often push the top of a storm’s circulation away from the surface center. Until these centers realign, substantial intensification is unlikely.

“A tropical cyclone has to stand up straight before it can intensify,” Fischer said. He noted that recognizing the signs of this transition earlier could provide coastal communities and emergency managers with vital additional time for evacuation and preparation.

The research team examined 1,510 radar analyses from 28 hurricane seasons spanning 1997 to 2024, using a database known as TC-RADAR (Tropical Cyclone Radar Archive of Doppler Analyses with Recentering). By comparing storms that successfully aligned with those that remained tilted, they pinpointed four specific characteristics that favor vertical alignment:

• A compact, tightly organized circulation near the ocean surface.
• A storm tilt positioned favorably relative to vertical wind shear, which refers to changes in wind speed or direction with height.
• Stronger rising air and heavier rainfall concentrated near the storm’s lower-level center.
• An environment featuring warm ocean water, high atmospheric moisture, and relatively weak winds in the middle levels of the atmosphere.

Fischer highlighted that storms which eventually aligned appeared distinct about a day before the transition occurred. They exhibited stronger, tighter surface circulations and more widespread, vigorous thunderstorms lifting air near the center. The study suggests these thunderstorms play an active role in pulling the leaning circulation upright, rather than merely serving as a visible indicator that strengthening is already underway.

Because NOAA reconnaissance aircraft already measure low-level wind strength, storm size, thunderstorm coverage, and tilt direction during operational flights, the newly identified features could help scientists evaluate whether high-resolution hurricane forecasting models accurately reproduce these physical processes. The results were published in the Journal of Geophysical Research: Atmospheres under the title “To Align or Not to Align? That Is the Question.”

Co-authors on the study include George R. Alvey III of the Cooperative Institute for Marine and Atmospheric Sciences and NOAA; Deelan Jariwala, a 2026 University of Miami graduate in meteorology and mathematics; and Paul D. Reasor of NOAA’s Hurricane Research Division. The work was supported by the National Science Foundation under award No. 2241605.