2025 Atlantic Hurricane Season

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 North Atlantic in June 2025. The system developed from a non-tropical disturbance that had been tracked for several days by the Continental Storm Service (CSS). Scatterometer passes on June 21 indicated that the disturbance already possessed a closed low-level circulation, though the system remained poorly organized and intermittently entangled with a nearby frontal zone. After gradually consolidating and detaching from the front, the cyclone was upgraded to Andrea at 12:00 UTC on June 24.

In this analysis, Andrea reached a peak intensity of 35 kn (40 mph; 65 km/h) and a minimum central pressure of 1014 hPa (29.94 inHg). The subtropical phase lasted only six hours. Dry-air entrainment and the loss of organized deep convection caused Andrea to degenerate into a remnant low later on June 24. Because Andrea remained over the open Atlantic throughout its lifetime, no effects on land were reported. The cyclone generated 0.1225 units of accumulated cyclone energy (ACE).

Meteorological history

The precursor disturbance was first noted on June 21 over the central Atlantic, near . Although the system lacked sustained deep convection, an ASCAT pass around midday indicated a closed surface circulation with peak winds of about 20 kn (23 mph; 37 km/h). Over the next 24 hours the disturbance drifted northward and then north-northeastward while remaining weak, with estimated winds fluctuating between 15 kn (17 mph; 28 km/h) and 20 kn (23 mph; 37 km/h) and pressures of 1017–1018 hPa. Throughout this period, the circulation was shallow and often partially embedded within a frontal environment.

By June 23 the system had become better defined. Scatterometer data showed a broader area of strong winds in the eastern semicircle, and the disturbance intensified to 25 kn (29 mph; 46 km/h) at 00:00 UTC while moving to the north-northeast. Six hours later, a closed low-level center remained evident, though the wind field was still asymmetric and the deepest convection was displaced from the circulation. Additional strengthening occurred through the day, and the system reached 30 kn (35 mph; 56 km/h) by 12:00 UTC on June 23 while continuing generally north-northeastward.

During the early hours of June 24, ASCAT and synthetic aperture radar data indicated that gale-force winds had developed in the southeastern semicircle. At the same time, microwave imagery depicted a compact but shallow vortex, with the primary convective bursts wrapped close to the center. After the circulation pulled away from the frontal boundary and acquired enough persistent near-center convection to satisfy the CSS criteria for subtropical classification, the system was designated Subtropical Storm Andrea at 12:00 UTC on June 24, centered near . Andrea attained its peak intensity at that time, with maximum sustained winds of 35 kn (40 mph; 65 km/h) and a pressure of 1014 hPa.

Andrea’s subtropical phase was brief. Increasing dry-air entrainment soon eroded the central convection, and by 18:00 UTC the cyclone had become a shallow, largely non-convective vortex. Although the low-level circulation remained well defined, the system no longer met the CSS definition of a subtropical cyclone and was analyzed as a remnant low. The circulation persisted into June 25 while gradually weakening over the open Atlantic.

Analysis and classification

The CSS operationally tracked Andrea as a compact cyclone embedded in a complex synoptic environment. The primary difficulty lay in distinguishing between a frontal gale low and a true subtropical cyclone. Early in the system’s life, visible imagery repeatedly showed a closed low-level swirl, but convection was weak, intermittent, and generally displaced from the center. These factors favored treatment as a disturbance rather than a named cyclone through June 23.

The upgrade on June 24 was based chiefly on the combination of scatterometer and SAR data, which showed sustained gale-force winds in the southeastern quadrant, and microwave imagery, which indicated a closed and coherent inner circulation. The cyclone remained asymmetric and shallow throughout its life; however, by 12:00 UTC on June 24 it appeared sufficiently detached from the frontal zone to support a subtropical classification. The relatively short-lived nature of the upgrade reflected the rapid onset of dry-air entrainment, which stripped the system of deep convection within six hours.

This analysis differs from the contemporaneous CSS operational record, which classified Andrea as a tropical storm rather than a subtropical storm. The reanalysis presented here retains a subtropical designation because the system never developed a consistently tropical cloud pattern, and its strongest winds remained concentrated in an asymmetric wind field rather than around a compact convective core.

Forecasting and model performance

Andrea was examined using a mixture of global, regional, and experimental guidance. During the early stages, the global GFS/AVNO guidance handled the broad track reasonably well and was among the better-performing models in depicting the disturbance as a weak and shallow low. It generally kept the system in the 13 kn (15 mph; 24 km/h) to 30 kn (35 mph; 56 km/h) range while showing only gradual organization, which aligned fairly well with the observed slow development.

Near peak intensity, the regional models performed unevenly. HMON was the closest to the adopted peak strength, generally showing a low- to mid-30-knot cyclone around June 24. HWRF and HFSA tended to be more aggressive, at times deepening Andrea to the upper 30-knot range and depicting a more compact inner-core structure than was evident in satellite imagery. These solutions appeared to overstate the extent of tropical transition.

The experimental machine-learning model TC-EVO, which used GFS fields together with GOES visible, infrared, and water-vapor imagery, consistently underestimated the cyclone’s strength. TC-EVO produced maximum-wind estimates of 17.1 kt at 18:00 UTC on June 21, 00:00 UTC on June 22, and 06:00 UTC on June 22, and 17.5 kt at 18:00 UTC on June 22. These values lagged the scatterometer-based analyses and did not capture the later subtropical-storm phase. In practice, TC-EVO was more useful as a conservative baseline than as a peak-intensity tool for this system.

Overall, no single model performed best throughout Andrea’s entire life cycle. The global guidance handled the system’s broad motion and eventual weakening more reliably, while HMON was the most accurate near the brief peak. The adopted analysis relied most heavily on scatterometer and SAR data, with satellite structure used primarily to determine the timing of subtropical transition and subsequent degeneration.

Impact

Andrea remained over the open Atlantic during its entire lifetime. No coastal watches or warnings were issued, and no damage or casualties were reported.

Storm summary

Date and time (UTC)	Status	Winds	Pressure	Position
12:00, June 21	Disturbance	23 mph	1017 hPa	30.5°N 57.0°W
18:00, June 21	Disturbance	23 mph	1017 hPa	29.8°N 57.4°W
00:00, June 22	Disturbance	17 mph	1018 hPa	30.0°N 57.6°W
06:00, June 22	Disturbance	23 mph	1017 hPa	30.5°N 57.6°W
12:00, June 22	Disturbance	23 mph	1017 hPa	31.0°N 57.6°W
18:00, June 22	Disturbance	23 mph	1017 hPa	31.5°N 57.4°W
00:00, June 23	Disturbance	29 mph	1016 hPa	32.0°N 57.0°W
06:00, June 23	Disturbance	29 mph	1015 hPa	32.6°N 56.3°W
12:00, June 23	Disturbance	35 mph	1015 hPa	33.3°N 55.1°W
18:00, June 23	Disturbance	35 mph	1015 hPa	33.9°N 54.0°W
00:00, June 24	Disturbance	40 mph	1014 hPa	34.7°N 53.0°W
06:00, June 24	Disturbance	40 mph	1014 hPa	35.4°N 51.4°W
12:00, June 24	Subtropical Storm	40 mph	1014 hPa	36.2°N 49.7°W

See also

• 2025 Atlantic hurricane season
• Subtropical cyclone
• Extratropical cyclone