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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 Spring (March 2026 - May 2026)

- In the tropics, positive sea surface temperature (SST) anomalies prevailed over the Pacific and Indian Ocean, with particularly strong positive anomalies around the dateline (Fig. S3). An oceanic Rossby wave associated with extremely warm water propagated eastward along the equator in the Pacific, resulting in a rapid increase in the NINO.3 index. Meanwhile, negative SST anomalies were observed along 20°N in the western North Pacific.
- Convective activity was extremely enhanced between 10°N and 20°N in the western North Pacific, while it was extremely suppressed between 10°S and 20°S in the central South Pacific and from the equatorial eastern Indian Ocean to the South China Sea.
- In the tropical upper troposphere (Fig. S5), cyclonic circulation anomalies were observed around the Indochina Peninsula and from the central North Pacific to the Caribbean Sea. Anticyclonic circulation anomalies were dominant in the zonal direction from East Asia to North America via the North Pacific, while significantly strong cyclonic circulation anomalies were observed northwest of Hawaii.
- In the tropical lower troposphere (Fig. S6), extremely strong cyclonic circulation anomalies extending toward the subtropics were observed from the western to the central North Pacific. From the central to the eastern equatorial Pacific, westerly and easterly anomalies were observed on the northern and southern sides of the equator, respectively.
- In the Northern Hemisphere, the zonal-mean subtropical jet stream was significantly shifted southward from its climatological position and was markedly weaker than normal between 25°N and 40°N from East Asia to the North Pacific and from North America to the North Atlantic, while the polar front jet stream was stronger than normal between 50°N and 60°N (Fig. S8).
- In the 500-hPa height field (Fig. S7), the main polar vortex was located over northeastern Canada, accompanied by significantly negative height anomalies. Negative height anomalies were also observed over central Siberia and around Turkey. Meanwhile, in the high latitudes, positive height anomalies were observed over northern Europe and eastern Siberia. In the midlatitudes, positive height anomalies prevailed from eastern Eurasia to the North Atlantic via the North Pacific and North America.
- Sea-level pressure anomalies were generally negative in the high latitudes, except from eastern Siberia to Alaska. In the midlatitudes, positive anomalies were dominant over the North Pacific and from the North Atlantic to Europe, while negative anomalies prevailed over Asia except for the Far East. Significantly negative anomalies prevailed over the subtropics in the eastern North Pacific.
- The characteristics of Japan's climate in spring were as follows (Fig. S1). Significantly above-normal temperatures were observed across Japan, and the seasonal anomaly of the average surface temperature over Japan was +1.54°C, the second-highest spring value since 1898. Precipitation amounts were near normal throughout Japan. Sunshine durations were above normal except on the Pacific side of western Japan, with significantly above-normal values on the Sea of Japan side of eastern Japan.

Supplemental information

- Climate Anomaly Table over Japan

Fig.S1 Seasonal climate anomaly/ratio over Japan (March 2026 - May 2026) 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 (March 2026 - May 2026) 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 (March 2026 - May 2026) The black lines show wind speed at intervals of 10 m/s. The brown lines show its normal at intervals of 20 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 (March 2026 - May 2026) 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 (March 2026 - May 2026) The contours show 850-hPa temperature at intervals of 3 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