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Seasonal Highlights on the Climate System

'Seasonal Highlights on the Climate System' has been issued since March 2007 as a seasonal bulletin focusing on the seasonal highlights of the monitoring results. For monthly information, please refer to 'Monthly Highlights on the Climate System.'

Notice: Products have been upgraded from PDF to HTML format starting from the issue of spring 2025 for improved accessibility.

Highlights in Autumn (September 2025 - November 2025)

- In the equatorial Pacific, remarkably positive SST anomalies were dominant in the western part, while negative SST anomalies were observed in the central and eastern parts (Fig. S3). This anomaly distribution was similar to that seen during a La Niña event, although it did not meet the criteria. In the Indian Ocean, remarkably positive SST anomalies were observed in the eastern tropics, while significantly negative SST anomalies were dominant in the western tropics, resulting in a record-breaking negative phase of the Indian Ocean Dipole. In the subtropical northwestern and southwestern Pacific, significantly positive SST anomalies were observed.
- The global distribution of large-scale divergence and convergence areas in the upper troposphere showed a wave number 1 pattern, with the center of divergence located around the Maritime Continent. Convective activity was especially enhanced from the Indochina Peninsula to the Philippines and from southern Indonesia to northern Australia (Fig. S4). In the tropical upper (Fig. S5) and lower (Fig. S6) troposphere, cyclonic and anticyclonic circulation anomalies straddling the equator were observed over the Pacific, respectively, and they were reversed from the Indian Ocean to the Maritime Continent. Lower-level anticyclonic anomalies were significant over the subtropical northwestern Pacific.
- In the Northern Hemisphere, the zonal-mean subtropical jet stream was located at its normal position and was stronger than normal (Fig. S8). Over East Asia, the subtropical jet stream was shifted northward until October, but shifted southward in November. In the upper troposphere, zonally elongated anticyclonic circulation anomalies were observed over mid-latitude Eurasia and were significant over the Middle East and East Asia.
- In the 500-hPa height field (Fig. S7), the polar vortex was located over Eastern Siberia, with negative anomalies around the Kamchatka Peninsula, while positive anomalies were dominant from Canada to Greenland. Positive anomalies were prevalent across most of the mid-latitudes except over the Atlantic, and they exceeded three times the standard deviation from eastern China to the East China Sea. Sea level pressure anomalies were negative except around Greenland and from Western Russia to Central Siberia, with significantly negative anomalies from the Aleutians to northern Canada (Fig. S9).
- The characteristics of the climate in Japan in autumn were as follows (Fig. S1). Remarkably above-normal temperatures were observed across Japan, and the seasonal anomaly of the average surface temperature was +1.37°C, the third-highest record for autumn since 1898. Precipitation amounts were above normal on the Sea of Japan side of northern and eastern Japan, while below normal on the Pacific side of eastern and western Japan, with significant anomalies on both sides of eastern Japan. Sunshine durations were above normal except on the Sea of Japan side of western Japan and on the Pacific side of eastern Japan, with significant anomalies in Okinawa/Amami and on the Pacific side of northern Japan.

Supplemental information

- Climate Anomaly Table over Japan

Fig.S1 Seasonal climate anomaly/ratio over Japan (September 2025 - November 2025) Top: temperature anomalies (degree C) Middle: precipitation ratio (%) Bottom: sunshine duration ratio (%) The base period for the normal is 1991-2020.

Fig.S7 Three-month mean 500-hPa height and anomaly in the Northern Hemisphere (September 2025 - November 2025) The contours show 500-hPa height at intervals of 60 m. The shading indicates its anomalies. The base period for the normal is 1991-2020.	Fig.S8 Three-month mean 200-hPa wind speed and vectors in the Northern Hemisphere (September 2025 - November 2025) The black lines show wind speed at intervals of 15 m/s. The brown lines show its normal at intervals of 30 m/s. The base period for the normal is 1991-2020.
Fig.S9 Three-month mean sea level pressure and anomaly in the Northern Hemisphere (September 2025 - November 2025) The contours show sea level pressure at intervals of 4 hPa. The shading indicates its anomalies. The base period for the normal is 1991-2020.	Fig.S10 Three-month mean 850-hPa temperature and anomaly in the Northern Hemisphere (September 2025 - November 2025) The contours show 850-hPa temperature at intervals of 4 degree C. The shading indicates its anomalies. The base period for the normal is 1991-2020.

Back Number

The descriptions from May-2011 to April-2021 issue are based on the former climatological normal (1981-2010 average).
In the descriptions until April-2011 issue, 1979-2004 average is used as climatological normal unless otherwise stated.
The descriptions until January-2014 issue are based on the JRA-25/JCDAS datasets.
The descriptions from February-2014 to April-2023 issue are based on the JRA-55 reanalysis.

Figures and Tables

Notice: Products based on JRA-3Q were updated to those with improved quality in terms of tropical cyclone analysis. OLR-related products from January 1991 are based on NOAA CPC Blended OLR (CBO).

Notice: Figures of 'Atmospheric Circulation', 'Time Cross Section', and 'Indices' have been revised with improved quality data regarding tropical cyclone analysis. (18 June 2024)

Notice: Depending on the availability of NOAA CPC Blended OLR (CBO) data, updates may be delayed or figures may be filled with gray indicating data missing.

• Explanation on the Products for Climate System Monitoring
• 3-month Mean Figures
• Time Cross Sections
• Indices
• Oceanic Figures and Tables