1. Climate in China

In August 2015, the mean precipitation over China was 105.1 mm, which was close to normal (105.3mm). The surface air temperature averaged over China was 21.1ºC, which was 0.3ºC above normal (20.8ºC). For the month, extremes of Daily Precipitation (DP), extremes of Continuous Precipitation (CP) and extremes of Continuous Precipitation Days (CPD) were observed in China.

2. General Circulation Features

Northern Hemisphere: During August 2015, in the field of mean 500hPa geopotential height anomaly, positive anomalies above 4 dam covered the regions from the central polar to mid-eastern Europe, form the southern Central Siberia to the northeastern Pacific via the Okhotsk and the Aleutian Islands, parts of northeastern North America. Meanwhile, negative anomalies below -4 dam were observed over the West Siberia, the northern North Atlantic, the northwestern Pacific and the Great Lakes. For the month, the northwestern Pacific subtropical high was stronger than normal, with the area larger than normal. The position of its western ridge point was westward than normal and its ridge line shifted southward than normal.

Southern Hemisphere: For the month, in the field of mean 500hPa geopotential height anomaly, positive anomalies over 4 dam were observed over the southwestern South Pacific Ocean, the southeastern South Indian Ocean and the southwestern South Atlantic. Meanwhile, negative anomalies below -4 dam covered from the western Antarctica to locations of the Southeast Pacific via the Antarctic Peninsula, and the central South Pacific.

3. Tropical Features

Sea Surface Temperatures (SSTs): In August 2015, SSTs were over 0.5℃ above in most of the central and eastern equatorial Pacific, with SSTs 3.0℃above normal around 120°W. Indices of Niño1+2，Niño3，Niño4，Niño3.4 and Niño Z were 2.3℃、2.4℃、1.0℃、2.0℃ and 1.8℃, respectively. The Indian Ocean Basin-Wide SSTA variation index (IOBW) was 0.6. The North Atlantic Triple (NAT) index was 1.5 and kept in the persistent positive phase.

Subsurface Temperatures: In August, the anomalously warm subsurface water shifted eastward to the region around 120-140°W, with the central values above 6℃. Meanwhile, the anomalously cool subsurface water controlled the equatorial western Pacific, with the central value below -2℃.

Warm Pools: For the month, the areas of both the Indian Ocean and the western Pacific warm pools were larger than normal and their intensities were both above normal.

Wind Field: For the month, at lower troposphere (850hPa), the westerly anomalies dominated over most equatorial Pacific, while the easterly anomalies dominated over the north of the equatorial Indian Ocean. At upper troposphere (200hPa), the westerly anomalies prevailed over most equatorial Indian Ocean and the eastern equatorial Pacific, while the easterly anomalies were observed over most of the equatorial Pacific west of 130°W.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was -1.7.

Convections over the Tropics: During August 2015, the anomalous outgoing longwave radiation (OLR) showed that convections were active around the central-eastern equatorial Pacific, with central values below -30W/m². However, convections were suppressed around the western equatorial Pacific.

4. ENSO Monitoring and Outlook

The El Nino index is expected to remain increasing and reach the peak in the winter of 2015/2016. There is a great chance that the El Nino will continue through the coming spring and develop into an extreme strong El Nino event.

 Therefore, we will closely monitor the development of ENSO conditions and update our ENSO wrap-up in time.