2025 Atlantic Hurricane Season

Subtropical Storm Andrea

Subtropical storm (SSHWS)
Duration	June 24, 2025 – June 24, 2025
Peak intensity	40 mph (65 km/h) (1-min); 1014 mbar (hPa)

Subtropical Storm Andrea was a short-lived subtropical cyclone in the central Atlantic Ocean in June 2025. The system originated from a compact non-tropical disturbance that the Continental Storm Service (CSS) began monitoring on June 21. Scatterometer data that day showed a closed low-level circulation despite the lack of persistent deep convection, but the system remained shallow and partly entangled with a frontal zone for several days. During this stage, Andrea was analyzed as a disturbance with winds generally between 15 and 25 mph and a central pressure of 1017 to 1018 hPa.

The disturbance gradually became better organized while moving north-northeastward. By June 23, scatterometer passes indicated a broader area of stronger winds in the eastern semicircle, and the system strengthened to 30 mph by 00:00 UTC and 35 mph by 12:00 UTC. Early on June 24, additional scatterometer and synthetic aperture radar data showed a compact gale area southeast of the center, while microwave imagery depicted a coherent but shallow inner vortex that had pulled away from the nearby frontal boundary. Based on that evolution, the CSS upgraded the cyclone to Subtropical Storm Andrea at 12:00 UTC on June 24. Andrea reached its peak intensity at that time, with maximum sustained winds of 40 mph and a minimum central pressure of 1014 hPa.

Andrea’s subtropical phase lasted only six hours. Soon after being named, the storm encountered increasing dry-air entrainment, and the already limited central convection quickly diminished. Satellite and microwave imagery later on June 24 showed that the cyclone remained tightly wound at low levels, but it no longer possessed enough organized deep convection to retain subtropical status. Accordingly, the CSS downgraded Andrea to a remnant low at 18:00 UTC on June 24. The remnant low persisted into June 25 while continuing northeastward over the open Atlantic, weakening to 35 mph by 00:00 UTC and remaining near that intensity through 12:00 UTC as it accelerated ahead of a larger mid-latitude trough.

The storm’s classification was one of the more difficult analyses of the season. Although Andrea developed a compact center and a gale-force wind field, its convection was intermittent and the circulation remained shallow and asymmetric throughout most of its life. The CSS therefore treated the cyclone as subtropical rather than tropical at peak intensity. The downgrade later on June 24 was based on the loss of organized central convection rather than a sudden collapse of the wind field, which remained well defined for some time after the system became post-tropical.

Model guidance handled Andrea unevenly. The experimental machine-learning system TC-EVO consistently lagged the cyclone’s actual development, keeping the precursor near 20 mph through June 22 and failing to capture the later strengthening into a subtropical storm. Among the dynamical models, the GFS/AVNO guidance performed best with the broad track and weakening trend, while HMON was generally the closest to the analyzed peak intensity. HWRF and HFSA were more aggressive, at times depicting a stronger and more tropical-looking cyclone than was supported by the satellite presentation. Once direct wind observations became unavailable after June 24, later intensity estimates relied more heavily on continuity, microwave structure, and the gradual degradation of the cloud pattern. Andrea remained over the open Atlantic throughout its lifetime and caused no known impacts on land.