Tropical Cyclone Courtney (27U/27S) - Post-Dissipation Analysis
Cyclone Courtney Development Timeline
- Naming Date: 26 March 2025 by Australian Bureau of Meteorology
- Peak Intensity: 29 March 2025 12:00 UTC - Category 4 Equivalent (JTWC: 130kt/240km/h, WMO/RSMC: 204km/h)
- Dissipation: 03 April 2025 06:00 UTC at 25.0°S 80.5°E
Intensity Progression (JTWC Scale)
Maximum Sustained Winds
| Date (UTC) | Intensity (kt) | Equivalent Category |
|---|---|---|
| 24 March 12:00 | 35 | Tropical Storm |
| 28 March 18:00 | 115 | Category 4 |
| 29 March 12:00 | 130 (Peak) | Category 4 |
| 03 April 06:00 | 30 | Dissipated |
Pressure Observations
- Minimum Recorded Pressure: 993 mb (01 April 06:00 UTC)
- Pressure at Dissipation: 1002 mb
Courtney's Track Characteristics
Movement Patterns
- Average Speed: 3-5 kt (5.5-9.2 km/h)
- Total Track Length: 2,850 km (1,770 mi)
- Notable Direction Shifts:
- 28 March: Sharp southwest turn at 17.2°S 94.6°E
- 01 April: Westward acceleration near 25.8°S 88.7°E
Key Positions
| Date (UTC) | Latitude | Longitude | Phase |
|---|---|---|---|
| Formation (24 Mar) | 16.6°S | 111.0°E | Initial development |
| Peak Intensity | 18.7°S | 90.1°E | Eyewall replacement |
| Final Position | 25.0°S | 80.5°E | Dissipation |
Structural Evolution of Courtney
Eyewall Dynamics
- First Eyewall Formation: 28 March 12:00 UTC (-17.3°S 94.6°E)
- Eyewall Replacement Cycle: Initiated 29 March 00:00 UTC
- Convective Collapse: 01 April 06:00 UTC observed through ASCAT imagery
Rainband Configuration
- Maximum Outflow: 1,200 km diameter (29 March)
- Dry Air Intrusion: Notable entrainment from NW quadrant after 30 March
Environmental Interactions
Sea Surface Temperatures
- Formation Zone: 29-30°C
- Dissipation Zone: 24-25°C
Vertical Wind Shear
| Phase | Shear Magnitude | Direction |
|---|---|---|
| Intensification | 10-15 kt | Easterly |
| Weakening | 50+ kt | Northwesterly |
Warning Timeline (JTWC)
| Advisory | Date (UTC) | Position | Max Winds | Significant Wave Height |
|---|---|---|---|---|
| NR 017 | 30 Mar 18:00 | 22.5°S 87.9°E | 70 kt | 25 ft |
| NR 020 | 01 Apr 09:00 | 25.1°S 88.3°E | 45 kt | 20 ft |
Post-Dissipation Analysis
Courtney's Meteorological Significance
- Rapid Intensification Rate: 55 kt/24h (28-29 March)
- Unusual Track Persistence: Maintained westward motion below 25°S
- Subtropical Transition: Completed 01 April 12:00 UTC
Operational Challenges
- Forecast Discrepancies:
- ECMWF underestimated southward component
- GFS overestimated interaction with mid-latitude trough
- Observation Gaps: Limited recon data due to remote location
Final observed position of Courtney at 25.0°S 80.5°E with residual swirl pattern visible on Himawari-9 imagery
Legacy in Cyclone Research
- Case study for subtropical transition mechanisms
- Validated new ASCAT-based intensity estimation techniques
- Contributed to WMO Task Force on Remote Sensing Applications