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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 changed from PDF to HTML format starting from the issue of May 2025 for improved accessibility.

Highlights in August 2026

- In the tropical Pacific, sea surface temperature (SST) anomalies were significantly positive east of the dateline, while they were near normal or negative west of the dateline. El Niño conditions intensified rapidly, and the NINO.3 index reached +3.4°C, the highest value on record for August (Fig. 8). Significantly positive SST anomalies were also observed between 35°N and 50°N, while negative SST anomalies prevailed between 25°N and 35°N in the western and central North Pacific. Positive SST anomalies were widespread in the tropical Indian Ocean and the North Atlantic, with significantly positive anomalies observed in many areas.
- In the tropics, convective activity was significantly enhanced over the central and eastern Pacific, while it was significantly suppressed from South America to the Maritime Continent via the Atlantic Ocean, Africa, and the Indian Ocean (Fig. 6). Convective activity was also enhanced along 20°N from the Bay of Bengal to the region east of the Philippines, indicating an active northwestern Pacific monsoon.
- In the tropical upper troposphere, pairs of anticyclonic and cyclonic anomalies straddling the equator were observed from the eastern Indian Ocean to the central Pacific and across a broad region extending from South America through the Atlantic and Africa to the western Indian Ocean, respectively (Fig. 8).
- In the tropical lower troposphere, significant cyclonic and anticyclonic anomalies straddling the equator were observed over the Pacific and from South America to Africa, respectively. Significant cyclonic anomalies prevailed in the subtropical northwestern Pacific (Fig. 9). The Southern Oscillation Index (SOI) was -1.4 (Fig. 5).
- In the Northern Hemisphere, the polar front jet stream was stronger than normal along the Arctic coast. The zonal-mean subtropical jet stream was displaced slightly from its climatological position and was stronger than normal between 20°N and 30°N. Over the Pacific, the subtropical jet stream exhibited a split-flow pattern (Fig. 11).
- In the 500-hPa height field (Fig. 10), a stronger-than-normal polar vortex was located over the Arctic Ocean. In the high latitudes, positive height anomalies prevailed except over the Arctic Ocean and northern Europe. In the mid-latitudes, positive height anomalies also prevailed, with significantly positive anomalies observed over Eurasia between 30°N and 40°N. Meanwhile, height anomalies were near normal over the Pacific between 30°N and 40°N and over the Atlantic along 40°N. Negative height anomalies were observed in the subtropics south of Japan.
- In the sea-level pressure (SLP) field (Fig. 12), positive anomalies prevailed north of 50°N, except over the Arctic Ocean and northern Europe, where negative anomalies were observed. In the Far East, significantly positive anomalies extended from central Siberia to Hokkaido, while significantly negative anomalies extended from southern China to the region southeast of Japan.
- Monthly mean temperatures were significantly above normal in western Japan, above normal in northern Japan, and near normal in eastern Japan and Okinawa/Amami (Fig. 1). The monthly mean surface air temperature anomaly averaged over Japan was +0.95°C, the seventh highest for August since 1898. Precipitation amounts were significantly above normal in Okinawa/Amami, while they were below normal in northern and western Japan, with significantly below-normal values on the Sea of Japan side of northern Japan. Sunshine durations were above normal in northern and western Japan, with significantly above-normal values on the Sea of Japan side of northern Japan, while they were below normal in Okinawa/Amami.

Climate in Japan (Fig. 1):

- Monthly mean temperature was significantly above normal in western Japan, because the region was covered by warm air associated with the subtropical jet stream, which was located further north than usual over Japan, and by high-pressure systems that brought frequent sunny days. The monthly anomaly of the average surface temperature over Japan was +0.95°C (7th warmest for August since 1898). On a longer time scale, the average surface temperatures have risen at a rate of about 1.35°C per century in August.
- On the Sea of Japan side of northern Japan, monthly precipitation was significantly below normal and monthly sunshine duration was significantly above normal because the region was frequently covered by high-pressure systems. In Okinawa/Amami, monthly precipitation was significantly above normal due to the influence of typhoons, including Typhoon DOLPHIN (T2613) and Typhoon SAUDEL (T2618), and moist air. In addition, eastern Japan experienced record-breaking heavy rain in some areas due to the effects of fronts and moist air.

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 +0.71°C (the warmest for August since 1891) (preliminary value) (Fig. 2). On a longer time scale, global average surface temperatures have risen at a rate of about 0.78°C per century in August (preliminary value).
- Extreme climate events were as follows (Fig. 3).
  - Monthly mean temperatures were extremely high from western Japan to northeastern China, in Southeast Asia, from the northwestern part of East Asia to the southern Middle East via Central Asia, from western Europe to the Mediterranean region, in the western part of Western Africa, from the southern part of North America to northern Chile via the northern part of South America and in southeastern Brazil.
  - Monthly precipitation amounts were extremely high in and around eastern Turkey, in and around northwestern Russia, in and around the northeastern USA, in and around northern Argentina and in southern Australia.
  - Monthly precipitation amounts were extremely low in Southeast Asia, from eastern to central Europe and from the southern USA to eastern Mexico.

Oceanographic Conditions:

- In the tropical Pacific, significantly positive SST anomalies were observed east of the dateline (Fig. 4). The monthly mean SST anomaly averaged over the NINO.3 region was +3.5°C and the SST deviation from the latest sliding 30-year mean over the region was +3.4°C (Fig. 5). In the western tropical Pacific, negative SST anomalies were observed except in some areas, including the region north of New Guinea.
- In the North Pacific, significantly positive SST anomalies were observed in the subtropics except around Hawaii, and in the latitudinal bands of 35°-50°N, except off the coast of North America.
- In the South Pacific, positive SST anomalies were widely observed except in the central subtropical region, and remarkably positive anomalies were observed in the eastern South Pacific and around New Zealand.
- In the Indian Ocean, positive SST anomalies prevailed over most areas, with significant positive anomalies in some regions.
- In the North Atlantic, significantly positive SST anomalies were observed off the west coast of Europe and in the subtropics.
- In the South Atlantic, positive SST anomalies were widespread with significant positive anomalies observed.

Tropics:

- Convective activity was extremely enhanced from the central to eastern Pacific between the equator and the ITCZ. It was extremely suppressed from South America to the western Pacific (Fig. 6). Convective activity was also enhanced along 20°N from the Bay of Bengal to the region east of the Philippines, indicating an active northwestern Pacific monsoon.
- The global distribution of convective activity anomalies exhibited a wave-number-1 pattern. The active phase of equatorial intraseasonal oscillation was unclear (Fig. 7).
- In the upper troposphere, paired anticyclonic circulation anomalies straddling the equator were observed from the eastern Indian Ocean to the central Pacific. Meanwhile, paired cyclonic circulation anomalies straddling the equator prevailed from South America to the western Indian Ocean (Fig. 8).
- In the lower troposphere, paired significant cyclonic circulation anomalies straddling the equator were seen around the Pacific. Meanwhile, paired significant anticyclonic circulation anomalies straddling the equator were prominently seen from South America to Africa, while significant cyclonic anomalies prevailed in the subtropical northwestern Pacific (Fig. 9).
- In the sea level pressure field, positive anomalies prevailed north of 50°N, except over the Arctic Ocean and around northern Europe, where negative anomalies were observed. In the Far East, significantly positive anomalies extended from central Siberia to Hokkaido, while significantly negative anomalies extended from southern China to the region southeast of Japan. The Southern Oscillation Index value was −1.4 (Fig. 5).

Extratropics:

- In the 500-hPa height field (Fig. 10), positive anomalies were seen in the high latitudes, except over the Arctic Ocean and northern Europe, where negative anomalies were seen. In the Northern Hemisphere mid-latitudes, generally positive anomalies were seen except over western Russia and the subtropics south of Japan, with significantly positive anomalies between 30°N and 40°N over Eurasia.
- The subtropical jet stream was slightly displaced northward over Eurasia and split into two branches over the Pacific, where the westerlies were weaker than normal between 40°N and 50°N (Fig. 11). The polar front jet stream was stronger than normal around 80°N.
- In the sea level pressure field (Fig. 12), negative anomalies were observed over the Arctic Ocean and northern Europe in the high latitudes. In the Northern Hemisphere mid-latitudes, negative anomalies were seen south of 40°N, with significant negative anomalies from southern China to the sea southeast of Japan. Positive anomalies were seen between 40°N and 60°N from East Asia to the Pacific.
- In the 850-hPa temperature field (Fig. 13), the anomaly pattern closely resembled that of the 500-hPa height field, with a weak zonal band of negative anomalies over the Pacific between 30°N and 40°N.

Zonal mean:

- In the zonal-mean zonal wind in the troposphere, the subtropical jet stream in the Northern Hemisphere was slightly displaced northward, with westerly anomalies between 20°N and 30°N. The polar front jet stream was stronger than normal around 80°N.
- The zonal mean temperatures in the troposphere were above normal over a wide area in the Northern Hemisphere, with significantly above-normal temperatures around 40°N and between 70°N and 80°N.

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 (August 2026) Top: temperature anomalies (°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 (August 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.11 Monthly mean 200-hPa wind speed and vectors in the Northern Hemisphere (August 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.12 Monthly mean sea level pressure and anomaly in the Northern Hemisphere (August 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.13 Monthly mean 850-hPa temperature and anomaly in the Northern Hemisphere (August 2026) The contours show 850-hPa temperature at intervals of 3 °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