Bohai Sea Ice Outlook for Winter 2024-2025
Michael Cooke, Meteorologist
The Bohai Sea is one of the most important bodies of water for international trade, with major Chinese ports such as Tianjin, Yingkou, and Jinzhou located on its shores which rank among the busiest in the world. The Bohai Sea accumulates ice during the winter due to influxes of cold air from Siberia. If the extent and density of this ice is high, this can cause major disruptions to vessels transiting through the Bohai Sea.
The two main factors that influence the development and extent of ice coverage over the Bohai Sea are Sea Surface Temperatures and Surface Air Temperatures, and how they compare to the climatological norm for the region.
Review of the Previous 2023-2024 Season
Ice extent in the Bohai Sea during the winter of 2023-24 was below average, with ice growth starting in late December and peaking from late January through early February. Coverage was especially prevalent in the Liaodong Bay throughout the season, but at its peak ice formation also took place along the coasts of the Laizhou and Bohai Bays. Melting occurred over the course of March at a slower pace than normal.
Figure 1: Left: Peak ice extent in the Bohai Sea on Jan 26th, 2024.
2024-25 Winter Season Forecast
At the start of last winter, Sea Surface Temperatures (SST’S) in the Bohai Sea were below average. However, approaching December this year SST’s were trending well above average, which typically correlates with a later than normal onset of ice development. This is the reason for the lack of any sea ice development thus far as of the writing of this outlook.
Figure 2: Sea surface temperature anomalies in the Yellow Sea on Nov 2023 (left) vs. Nov 2024 (right).
However, for Surface Air Temperatures, these are expected to remain below normal for the remainder of December. This will help to counteract the above normal SST’s, and therefore ice growth is therefore expected to gradually increase over the next 3 weeks after the later start to the ice season.
Figure 3 : CFSv2 500mb heights and height anomaly for the month of December, indicating below normal air temperatures.
For forecasting long-term Surface Air Temperatures for the remainder of Winter, we can look at climate data for the mid-levels of the atmosphere (i.e. the 500mb pressure level), for January and February. On the below charts, the warm colors indicate positive height anomalies at 500mb (i.e. mid-level atmosphere warming), while cooler colors indicate negative height anomalies at 500 mb (i.e. mid-level atmosphere cooling). The mid-level warming or cooling will generally correlate well with what one can expect for temperatures at the surface level.
Moving into the heart of winter, positive height anomalies 500mb are expected for the Bohai Sea for January, while slightly less positive during February. This would indicate above average temperatures likely for January, and near normal for February. We would anticipate a slower than normal rate of ice development during January, followed by near normal rate of ice development during February.
Figure 4 : CFSv2 500mb heights and height anomaly for the months of January and February, indicating above average air temperatures in January, and slightly above average to near normal temperatures during February.
In summary, we note the following:
- Warmer than normal Sea Surface Temperatures to begin this season
- Cooler than normal Surface Air Temperatures through the end of December
- Warmer than normal Surface Air Temperatures for January, followed by near normal Surface Air Temperatures for February
Based on the above metrics, for the 2024-2025 season we anticipate a near normal rate of ice development for December, to likely be followed by a slowing of ice development in January. Then, early indications are for ice development to increase again in February, with the annual peak ice extent likely to occur in mid-February. WRI will continue to monitor sea ice conditions in the Bohai Sea, and keep you well advised on potential impacts to your transits.
