1. Climate in China

In May 2015, the surface air temperature averaged over China was 16.8ºC, with 0.6ºC above normal (16.2ºC). The mean precipitation was 80.0 mm over China, which was 15.1% more than normal (69.5mm). For the month, extremes of Daily Precipitation (DP) and High Temperature (HT) were observed in China.

2. General Circulation Features

Northern Hemisphere: During May 2015, in the field of mean 500hPa geopotential height anomaly, positive anomalies above 4 dam covered western Siberia, northeastern North Pacific Ocean, central eastern North America and northeastern North Atlantic Ocean. Meanwhile, negative anomalies below -4 dam covered Okhotsk Sea, western North America and central northern North Atlantic Ocean. During the month, the northwestern Pacific subtropical high was stronger than normal, with the area bigger than normal. The position of its west ridge shifted further westward and northward than normal.

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

3. Tropical Features

Sea Surface Temperatures (SSTs): In May 2015, SSTs were over 0.5℃ above normal in most of the central and eastern equatorial Pacific, especially above 1℃ in some parts. Indices of Niño1+2，Niño3，Niño4，Niño3.4 and Niño Z were 2.5℃，1.2℃，1.1℃，1.0℃ and 1.3℃, respectively. The Indian Ocean Dipole (IOD) index was 0.6, indicating the development of positive phase of Indian Ocean Dipole mode. The North Atlantic Triple (NAT) index was 1.6 and kept in the persistent positive phase.

Subsurface Temperatures: In May, the anomalously warm subsurface water shifted eastward to the equatorial eastern Pacific around 120°W. Meanwhile, the anomalously cool subsurface water controlled the equatorial western Pacific, with the central value below -2℃ west to 140ºE.

Warm Pools: For the month, the area of the Indian Ocean warm pool and the western Pacific warm pool were slightly larger than normal, and the intensity was greatly above normal.

Wind Field: For the month, at lower troposphere (850hPa), the westerly anomalies dominated over most equatorial Pacific and western equatorial Indian Ocean while the easterly anomalies dominated over eastern equatorial Indian Ocean. At upper troposphere (200hPa), the westerly anomalies prevailed over the region from the equatorial Indian Ocean to the Maritime Continent and eastern equatorial eastern Pacific, while the easterly anomalies ruled the most equatorial central-western Pacific.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was -1.0.

Convections over the Tropics: During May 2015, the anomalous outgoing longwave radiation (OLR) showed that convections were active around the tropical central-eastern Pacific, with central values below -30 W/m². However, convections were suppressed around the South China Sea, Maritime Continent, and the tropical western Pacific, with central values above 15 W/m².

4. ENSO Monitoring and Outlook

Based on the diagnoses of precursory factors and predictions of dynamical and statistical models, the El Nino event will last through the 2015/2016 winter, and be likely to reach the strong level.

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