1. Climate in China

In September 2015, the surface air temperature averaged over China was 16.9℃, with 0.3℃ above normal (16.6℃). The mean precipitation was 72.4 mm over China, which was 10.9% more than normal (65.3mm). For the month, extremes of Consecutive Precipitation Day (CPD) were observed in China.

2. General Circulation Features

Northern Hemisphere: During September 2015, in the field of mean 500hPa geopotential height anomaly, positive anomalies above 4 dam covered western Europe, east of Okhotsk Sea, northeastern North America. Meanwhile, negative anomalies below -4 dam covered northwestern North America. During the month, the northwestern Pacific subtropical high was weaker than normal, with the area smaller than normal. The position of its west ridge shifted further westward than normal.

Southern Hemisphere: For the month, in the field of mean 500hPa geopotential height anomaly, positive anomalies over 4 dam were observed over southeastern and southwestern South Pacific Ocean and southwestern South Indian Ocean. Meanwhile, negative anomalies below -4 dam covered central South Pacific Ocean and southern South Atlantic Ocean, with central values below -12 dam over parts of southern South Atlantic Ocean.

3. Tropical Features

Sea Surface Temperatures (SSTs): In September 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 2.6℃、2.6℃、1.1℃、2.3℃ and 2.0℃, respectively. The Indian Ocean Basin-Wide SSTA variation index (IOBW) was 0.6. The North Atlantic Triple (NAT) index was 1.0.

Subsurface Temperatures: In September, the anomalously warm subsurface water shifted eastward to the region around 100-135°W, with the central values above 6℃. Meanwhile, the anomalously cool subsurface water controlled over 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 easterly anomalies prevailed over most equatorial Pacific Ocean, while the westerly anomalies were observed over most of the equatorial Indian Ocean.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was -1.6.

Convections over the Tropics: During September 2015, the anomalous outgoing longwave radiation (OLR) showed that convections were active over the equatorial Pacific region to the east of 150°E, with central values below -30 W/m². However, convections were suppressed around the western equatorial Pacific and the eastern equatorial Indian Ocean.

4. ENSO Monitoring and Outlook

Based on the prediction of domestic and foreign climate models and statistic methods, El Nino will keep increasing and arrive its peak during boreal winter 2015-2016. It will continue until the spring of 2016, most likely forming an extremely strong El Nino event.

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