Monthly Highlights on the Climate System

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

Highlights in April 2025

- The tripole pattern of positive, negative, and positive sea surface temperature (SST) anomalies in the equatorial Pacific Ocean weakened but persisted. Positive SST anomalies prevailed over the Indian Ocean.
- Convective activity was enhanced around the maritime continent, while suppressed in the western Indian Ocean. From the western to central equatorial Pacific, active and suppressed convection was observed in the Southern Hemisphere side and the Northern Hemisphere side, respectively.
- In the upper troposphere, corresponding to the convective activity, anti-cyclonic circulation anomalies were seen over Southeast Asia and Australia.
- In the 500-hPa height field of the Northern Hemisphere, the main polar vortex located in the Barents Sea and significant positive anomalies were seen over northern Europe and the Sea of Okhotsk. Positive anomalies were dominant in the mid-latitudes while weak negative anomalies were seen over East Asia.
- The subtropical jet stream meandered over East Asia resulting the southward shift near Japan.
- In the sea level pressure field, negative anomalies were seen over East Asia and a pressure trough formed from the Yellow Sea to the Sea of Japan.
- Monthly mean temperatures were above normal in northern/eastern/western Japan while below normal in Okinawa/Amami. Monthly sunshine durations were the lowest for April since 1946 in the Sea of Japan side and the Pacific side of northern Japan.

Full version (PDF)

Monthly Highlights on the Climate System (April 2025)
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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.

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Tokyo Climate Center, Climate Prediction Division.
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