TCC home About TCC Site Map Contact us

Monthly Highlights on the Climate System

'Monthly Highlights on the Climate System' has been issued since March 2007 as a monthly bulletin focusing on the monthly highlights of the monitoring results.

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

Highlights in May 2025

- Significant positive sea surface temperature (SST) anomalies were seen around the Maritime Continent, and negative SST anomalies were observed in the eastern equatorial Pacific. Positive SST anomalies also prevailed over the southern tropical Indian Ocean. The NINO.3 index was -0.2°C.
- Convective activity was enhanced from India to around the Maritime Continent, while suppressed in the western North Pacific and from Africa to the western Indian Ocean. The onset of the Indian monsoon was earlier than normal (India Meteorological Department).
- In the upper troposphere, anti-cyclonic circulation anomalies straddling the equator were seen over the Indian Ocean. In the lower troposphere, cyclonic and anti-cyclonic circulation anomalies straddling the equator were seen from the Indian Ocean to the western Maritime Continent and over the Pacific, respectively.
- In the 500-hPa height field of the Northern Hemisphere, a stronger-than-normal polar vortex was located in the northern Canada. Positive and negative anomalies were seen over the western Europe and the eastern Europe, respectively. Positive and negative anomalies were seen over the northern Far East and the southern Far East, respectively. Positive anomalies were dominant over the Central Asia and the mid-latitudes of the North Pacific.
- The subtropical jet stream meandered over East Asia, resulting in a southward shift over China and a northward shift over the east of Japan. In the sea level pressure field, a pressure trough formed along the main island of Japan.
- Monthly mean temperatures were above normal in northern Japan. On the Pacific sides of eastern and western Japan, monthly sunshine durations and monthly precipitation amounts were below and above normal, respectively, especially significant for the Pacific side of eastern Japan.

Climate in Japan (Fig. 1):

- Monthly mean temperatures were above normal in northern Japan, because the region was likely to be affected by warm air. The monthly anomaly of the average surface temperature over Japan was +0.51°C. On a longer time scale, the average surface temperatures have risen at a rate of about 1.73°C per century in May.
- Monthly precipitation amounts were significantly above normal on the Pacific side of eastern Japan and were above normal on the Sea of Japan side of western Japan, on the Pacific side of western Japan and in Okinawa/Amami. Monthly sunshine durations were significantly below normal on the Pacific side of eastern Japan and were below normal on the Pacific side of western Japan. The regions were well-affected by low-pressure systems and fronts.

World Climate:

- The monthly anomaly of the global average surface temperature (i.e., the combined average of the near-surface air temperature over land and the SST) was +0.43°C (2nd warmest for May since 1891) (preliminary value) (Fig. 2). On a longer time scale, global average surface temperatures have risen at a rate of about 0.77°C per century in May (preliminary value).
- Extreme climate events were as follows (Fig. 3).
  - Monthly mean temperatures were extremely high from western China to Central Asia and from southern Mexico to Colombia via Caribbean countries.
  - Monthly mean temperatures were extremely low from central to southern India.
  - Monthly precipitation amounts were extremely high from eastern to western Japan, from Viet Nam to Thailand, from Bangladesh to India and from Paraguay to northeastern Argentina.

Oceanographic Conditions:

- In the equatorial Pacific, negative SST anomalies were observed in the eastern part, and remarkably positive SST anomalies were observed around Indonesia (Fig. 4). The monthly mean SST anomaly averaged over the NINO.3 region was -0.3°C and the SST deviation from the latest sliding 30-year mean over the region was -0.2°C (Fig. 5).
- In the North Pacific, remarkably positive SST anomalies were observed from the seas east of the Philippines to the south of Japan and around the dateline in the tropics and the mid-latitudes, and remarkably negative SST anomalies were observed to the southwest of California.
- In the South Pacific, remarkably positive SST anomalies were observed in the western part from the tropics to the mid-latitudes, the eastern part of the subtropics and the central part of the mid-latitudes.
- In the Indian Ocean, remarkably positive SST anomalies were observed in the Bay of Bengal and on the Southern Hemisphere side.
- In the North Atlantic, remarkably positive SST anomalies were observed in the western part of the subtropics and to the west of Europe.
- In the South Atlantic, remarkably positive SST anomalies were observed in the mid-latitudes.

Tropics:

- Convective activity was enhanced from India to the north of Australia via Indonesia, and suppressed from Africa to the Middle East and the tropical western North Pacific (Fig. 6).
- Eastward propagation of the active phase of equatorial intraseasonal oscillation was unclear (Fig. 7).
- In the upper troposphere, anti-cyclonic circulation anomalies straddling the equator were seen over the eastern Indian Ocean. A wavy anomaly pattern was seen from around India to the North Pacific via southern China, with anti-cyclonic circulation anomalies to the east of Japan. Cyclonic circulation anomalies were seen over the subtropical western to central Pacific (Fig. 8).
- In the lower troposphere, cyclonic circulation anomalies were seen over from the Arabian Sea to northern Indonesia, and anti-cyclonic circulation anomalies were seen over the tropical Pacific (Fig. 9).
- In the sea level pressure field, negative anomalies were seen over the Middle East and from the Indian Ocean to the tropical western Pacific, and positive anomalies were seen over the subtropical western North Pacific. The Southern Oscillation Index value was +0.7 (Fig. 5).

Extratropics:

- In the 500-hPa height field (Fig. 10), the polar vortex was stronger than normal around northern Canada. A wavy anomaly pattern was seen from the North Atlantic to the western North Pacific, with positive anomalies to the west of Europe, over Central Asia and to the east of Japan, and negative anomalies over eastern Europe and northeastern China.
- The subtropical jet stream shifted southward over China, while the westerly jet stream shifted northward from Japan to the North Pacific, compared to its normal position (Fig. 11). The polar-front jet stream meandered over Eurasia, and split into two branches around the Far East.
- In the sea level pressure field (Fig. 12), positive anomalies were seen over western Europe and the mid-latitude North Pacific, and negative anomalies were seen around Greenland, from eastern China to southern Eastern Siberia, and around Alaska. The extension of the North Pacific subtropical high toward south of Japan was stronger than normal.
- Temperatures at 850-hPa were above normal to the west of Europe, over Central Asia and to the east of Japan, and negative anomalies over eastern Europe and northeastern China (Fig. 13).

Zonal mean:

- In the zonal mean zonal wind in the troposphere, westerly anomalies were seen in the latitude bands of 50°N and 45°S, and easterly anomalies were seen in the latitude bands of 30°N, 20-30°S, and 60°S.
- The zonal mean temperatures in the troposphere were above normal except in the Southern Hemisphere mid-latitudes.

Supplemental information

- Climate Anomaly Table over Japan
- Extratropics in the Southern Hemisphere
- Snow in the Northern Hemisphere
- Arctic sea ice (link to the National Snow and Ice Data Center)

Fig.1 Monthly climate anomaly/ratio over Japan (May 2025) Top: temperature anomalies (degree C) Middle: precipitation ratio (%) Bottom: sunshine duration ratio (%) The base period for the normal is 1991-2020.

Fig.10 Monthly mean 500-hPa height and anomaly in the Northern Hemisphere (May 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.11 Monthly mean 200-hPa wind speed and vectors in the Northern Hemisphere (May 2025) 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.12 Monthly mean sea level pressure and anomaly in the Northern Hemisphere (May 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.13 Monthly mean 850-hPa temperature and anomaly in the Northern Hemisphere (May 2025) 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
• 5-day Mean Figures
• 10-day Mean Figures
• Monthly Mean Figures
• 3-month Mean Figures
• Time Cross Sections
• Indices
• Oceanic Figures and Tables