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| | === Subtropical Storm Andrea === |
| <div class="tc-storm"> | | <div class="tc-storm"> |
| {{Infobox tropical cyclone small | | {{Infobox tropical cyclone small |
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| | Type = subtropical | | | Type = subtropical |
| | Formed = June 24, 2025 | | | Formed = June 24, 2025 |
| | Image = Andrea_2025-june_Peak.png | | | Image = Andrea_2025_June_Peak.png |
| | Dissipated = June 24, 2025 | | | Dissipated = June 24, 2025 |
| | Pressure = 1014 | | | Pressure = 1014 |
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| </div> | | </div> |
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| | '''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. |
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| '''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.
| | 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. |
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| In this analysis, Andrea reached a peak intensity of {{convert|35|kn|mph km/h|abbr=on}} 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|accumulated cyclone energy]] (ACE).
| | 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. |
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| ==Meteorological history==
| | 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. |
| The precursor disturbance was first noted on June 21 over the central Atlantic, near {{coord|30.5|N|57.0|W|type:weather_event_region:Atlantic_Ocean|display=inline}}. Although the system lacked sustained deep convection, an ASCAT pass around midday indicated a closed surface circulation with peak winds of about {{convert|20|kn|mph km/h|abbr=on}}. Over the next 24 hours the disturbance drifted northward and then north-northeastward while remaining weak, with estimated winds fluctuating between {{convert|15|kn|mph km/h|abbr=on}} and {{convert|20|kn|mph km/h|abbr=on}} and pressures of 1017–1018 hPa. Throughout this period, the circulation was shallow and often partially embedded within a frontal environment. | |
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| 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 {{convert|25|kn|mph km/h|abbr=on}} 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 {{convert|30|kn|mph km/h|abbr=on}} by 12:00 UTC on June 23 while continuing generally north-northeastward.
| | Model guidance handled Andrea unevenly. The experimental machine-learning system '''[[Tropical Cyclone EVOlution Model|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. |
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| 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 {{coord|36.2|N|49.7|W|type:weather_event_region:Atlantic_Ocean|display=inline}}. Andrea attained its peak intensity at that time, with maximum sustained winds of {{convert|35|kn|mph km/h|abbr=on}} and a pressure of 1014 hPa.
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| 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.
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| ==Analysis and classification==
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| 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.
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| 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.
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| 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.
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| ==Forecasting and model performance==
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| 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 {{convert|13|kn|mph km/h|abbr=on}} to {{convert|30|kn|mph km/h|abbr=on}} range while showing only gradual organization, which aligned fairly well with the observed slow development.
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| 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.
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| 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.
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| 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.
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| ==Impact==
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| Andrea remained over the open Atlantic during its entire lifetime. No coastal watches or warnings were issued, and no damage or casualties were reported. | |
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| ==Storm summary==
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| {| class="wikitable sortable"
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| ! Date and time (UTC)
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| ! Status
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| ! Winds
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| ! Pressure
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| ! Position
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| |-
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| | 12:00, June 21
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| | Disturbance
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| | 23 mph
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| | 1017 hPa
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| | 30.5°N 57.0°W
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| |-
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| | 18:00, June 21
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| | Disturbance
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| | 23 mph
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| | 1017 hPa
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| | 29.8°N 57.4°W
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| |-
| |
| | 00:00, June 22
| |
| | Disturbance
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| | 17 mph
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| | 1018 hPa
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| | 30.0°N 57.6°W
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| |-
| |
| | 06:00, June 22
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| | Disturbance
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| | 23 mph
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| | 1017 hPa
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| | 30.5°N 57.6°W
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| |-
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| | 12:00, June 22
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| | Disturbance
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| | 23 mph
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| | 1017 hPa
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| | 31.0°N 57.6°W
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| |-
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| | 18:00, June 22
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| | Disturbance
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| | 23 mph
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| | 1017 hPa
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| | 31.5°N 57.4°W
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| |-
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| | 00:00, June 23
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| | Disturbance
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| | 29 mph
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| | 1016 hPa
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| | 32.0°N 57.0°W
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| |-
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| | 06:00, June 23
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| | Disturbance
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| | 29 mph
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| | 1015 hPa
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| | 32.6°N 56.3°W
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| |-
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| | 12:00, June 23
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| | Disturbance
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| | 35 mph
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| | 1015 hPa
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| | 33.3°N 55.1°W
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| |-
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| | 18:00, June 23
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| | Disturbance
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| | 35 mph
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| | 1015 hPa
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| | 33.9°N 54.0°W
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| |-
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| | 00:00, June 24
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| | Disturbance
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| | 40 mph
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| | 1014 hPa
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| | 34.7°N 53.0°W
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| |-
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| | 06:00, June 24
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| | Disturbance
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| | 40 mph
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| | 1014 hPa
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| | 35.4°N 51.4°W
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| |-
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| | 12:00, June 24
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| | Subtropical Storm
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| | 40 mph
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| | 1014 hPa
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| | 36.2°N 49.7°W
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| |}
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| ==See also==
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| * [[2025 Atlantic hurricane season]]
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| * [[Subtropical cyclone]]
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| * [[Extratropical cyclone]]
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| {{reflist}}
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| [[Category:2025 Atlantic hurricane season]]
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| [[Category:Atlantic subtropical storms]]
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| [[Category:June 2025 events in North America]]
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| [[Category:Tropical cyclones in 2025]]
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| 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.
