1. Climate in China

In September 2014, the surface air temperature averaged over China was 17.1ºC, which was 0.5ºC below normal (16.1ºC). The mean precipitation over China was 80.7 mm, which was 23.6% above normal (65.3mm). For the month, extremes of Daily Precipitation (DP), Consecutive Precipitation (CP) and Consecutive Precipitation Day (CPD) were observed in China.

2. General Circulation Features

Northern Hemisphere: During September 2014, in the 500hPa geopotential height anomaly field, positive anomalies above 4 dam covered the regions from northeastern North Atlantic to the northern Central Europe, Sea of Okhotsk to Bering Sea, with central values above 8 dam in the region from Norwegian Sea to Scandinavian Peninsula. Meanwhile, negative anomalies below -4 dam covered northwestern Asia, southwestern North Pacific, northeastern North America, parts of southeastern North Atlantic, with central values below -8 dam.

For the month, the northwestern Pacific subtropical high was stronger than normal, and its area was above the normal. And, its position shifted further westward and southward than normal.

Southern Hemisphere: For the month, in the 500hPa geopotential height anomaly field, positive anomalies over 4 dam were observed over most of the South Polar region, parts of the southeastern South Pacific, with central values above 16 dam near the Antarctic Peninsula. Meanwhile, negative anomalies below -4 dam mainly covered the central and southern South Indian Ocean, parts of the central and southern South Pacific, with central values below -8 dam.

3. Tropical Features

Sea Surface Temperatures (SSTs): In September 2014, SSTs were over 0.5℃ above normal in most equatorial Pacific, especially above 1℃ in the western equatorial Pacific to the west of Dateline and most of the eastern equatorial Pacific near 120ºW and the coast of South America. Indices of Niño1+2，Niño3，Niño4，Niño3.4 and Niño Z were 0.9℃，0.4℃，0.7℃，0.5℃ and 0.6℃, respectively. The negative Indian Ocean Dipole (IOD) persisted in September but was slightly weaker than last month, with SSTs near normal in the tropical western Indian Ocean and over 0.5℃ above normal in the southeastern Indian Ocean. The IOD index was -0.4℃. SSTs were near normal in the tropical Atlantic Ocean.

Subsurface Temperatures: In September, anomalously warm subsurface water controlled most equatorial Pacific, with two warm centers located respectively at 165ºE and to the east of the Dateline around 135ºW. Their central values were above 2℃ and 3℃, respectively. In the eastern equatorial Pacific, the anomalously cold subsurface water was weak, with the cold center around 100ºW and central values below -2℃.

Warm Pools: For the month, the area of Indian Ocean warm pool was near normal, and the area of western Pacific warm pool was larger than normal. Both of their intensities were significantly stronger than normal.

Wind Field: For the month, at lower troposphere (850hPa), westerly anomalies dominated over most central and western equatorial Pacific, with central values above 2 m/s. And the eastern equatorial Pacific was controlled by weak easterly anomalies. At upper troposphere (200hPa), easterly anomalies prevailed over most central and western equatorial Pacific, with central values below -4 m/s. Meanwhile, the eastern equatorial Pacific was controlled by westerly anomalies, with central values above 8 m/s.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was -0.6.

Convections over the Tropics: During September 2014, the anomalous outgoing longwave radiation (OLR) showed that convections were active over the eastern tropical Pacific to north of the equator and the western tropical Pacific around 150ºW, with central values below -15W/m². Convection was also active over the central-western tropical Indian Ocean, with central values below -15W/m². Convection over the tropical Atlantic Ocean was near normal or inactive.

4. ENSO Monitoring and Outlook

Based on the criterion of ENSO operation of National Climate Center of China Meteorology Administration, the Niño Z index having exceeded 0.5℃ continuously since May 2014, we predict that the index will continue to stand on 0.5℃ in October 2014 and a weak El Nino event will come out.

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