Latest Southern Ocean Storm Trends: July–September 2025
Storm activity in the Southern Ocean is expected to follow distinct atmospheric patterns over the coming months. Pressure variations will significantly influence storm development across key maritime regions, particularly affecting routes around the Cape of Good Hope, Tasman Sea, and Cape Horn.
Storm Trend Outlook
At Weathernews, we regularly update our storm trend forecasts to keep you informed. Our latest Storm Trend Outlook for July through September 2025 covers key developments across the Southern Ocean, focusing on critical shipping routes around southern continents.
Southern Ocean Storm Trends
July 2025
Low-pressure conditions develop around the Cape of Good Hope, the Tasman Sea, and Cape Horn. High-pressure systems strengthen in the South Pacific and western South Atlantic. Stormy weather becomes more likely in the blue dotted areas, while calmer conditions persist in high-pressure zones.
- Fig.1 Monthly sea level pressure anomaly simulation for Jul. 2025 (JMA) ※Yellow indicates higher pressure, and blue indicates lower pressure compared with normal year: (hPa)
Industry Insights: Storm systems will intensify around major southern capes, while vessels transiting the South Pacific and western South Atlantic can expect more favorable conditions.
August 2025
Low atmospheric pressure persists from Australia to the Tasman Sea and around Cape Horn. Higher-than-average atmospheric pressure continues in the South Pacific. Severe weather conditions increase compared to normal patterns in affected areas.
- Fig.2 Monthly sea level pressure anomaly simulation for Aug. 2025 (JMA)
Industry Insights: Vessels navigating between Australia and the Tasman Sea should prepare for more challenging conditions, while South Pacific routes remain relatively stable with fewer severe weather events.
September 2025
Pressure patterns show minimal change from August conditions. Severe weather persists from Australia to the Tasman Sea and around Cape Horn. The South Atlantic experiences less severe weather than normal seasonal patterns.
- Fig. 3 Monthly sea level pressure anomaly simulation for Sep. 2025 (JMA)
Industry Insights:
Consistent stormy conditions continue in the Australia-Tasman Sea corridor and Cape Horn region, while South Atlantic routes offer more favorable conditions for maritime operations.
Normal Year Conditions in Southern Ocean
- Fig.4 The mean significant wave height of the past five years (WNI analysis). (Top) July; (Middle) August; (Bottom) September
These baseline conditions help maritime professionals understand how the forecast period compares to typical Southern Ocean weather patterns during the winter months.
Main Expected Areas of Stormy Conditions:
- July: Around the Cape of Good Hope, the Tasman Sea, around Cape Horn
- August: Australia to the Tasman Sea, around Cape Horn
- September: Australia to the Tasman Sea, around Cape Horn
Maritime operators should plan accordingly for these regional variations when scheduling voyages through Southern Ocean routes during the July-September 2025 period.
