1. Climate in China
In May 2016, the surface air temperature averaged over China was 16.3ºC, with 0.1ºC above normal (16.2ºC). The mean precipitation was 82.8 mm over China, which was 19.2% above normal (69.5 mm). For the month, extremes of Daily Precipitation Amount were observed in China.
2. General Circulation Features
Northern Hemisphere: During May 2016, in the field of mean 500hPa geopotential height anomaly, positive anomalies above 4 dam covered the regions from the East European Plain to northeastern Pacific via the Arctic region, from the Sea of Japan to northwestern Pacific, center North Africa, some parts of northern and central Atlantic, with the central value over 8 dam over the East European Plain, areas around the North Pole and locations of northeastern Pacific. Meanwhile, negative anomalies below -4 dam were observed over Central Siberian Plateau, form northeastern Pacific to Midwestern North America. During the month, the northwestern Pacific subtropical high was stronger than normal, with the area larger than normal, and extended further westward and shifted northward than normal.[P1]
Southern Hemisphere: For the month, in the field of mean 500hPa geopotential height anomaly, the positive anomalies over 4 dam were observed over the regions from southern South America to Antarctic Peninsula, eastern East Antarctica to southern Southwest Pacific，central South Pacific and the ocean to the south of Africa, with the central value exceeding 16 dam over the Drake Passage. Meanwhile, the negative anomalies below -4 dam covered form the southern Indian Ocean to New Zealand, southern South Atlantic Ocean and southeastern Pacific, with the central value below -12 dam.
3. Tropical Features
Sea Surface Temperatures (SSTs): In May 2016, SSTs were over -0.5℃ below normal in most of the eastern equatorial Pacific. Indices of Niño1+2，Niño3，Niño4，Niño3.4 and Niño Z were 0.3℃，0℃，0.6℃，0.3℃ and 0.3℃, respectively. The Indian Ocean Basin-Wide SSTA variation index (IOBW) was 0.7. The North Atlantic Triple (NAT) index was 1.3.
Subsurface Temperatures: For the month, the anomalously cool subsurface water controlled over the most of the equatorial Pacific, with the center located in the eastern Pacific, and the central value below -4℃.
Warm Pools: For the month, the areas of both the Indian Ocean and the western Pacific warm pools were larger than normal. Meanwhile, their intensities were evidently above normal.
Wind Field: For the month, at lower troposphere (850hPa), the weak westerly anomalies dominated over most of the central-eastern equatorial Pacific and most of Indian Ocean, while the easterly anomalies dominated over the region north to equator over West Pacific. At upper troposphere (200hPa), the weak easterly anomalies prevailed over the eastern equatorial Pacific Ocean while the westerly anomalies dominated over the central and western equatorial Pacific.
Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was 0.2.
Convections over the Tropics: During the month, the anomalous outgoing longwave radiation (OLR) showed that convections were active near the dateline to the south of equator and some parts of equatorial Indian Ocean, with central value below -30 W/m2. However, convections were suppressed in locations of equatorial West Pacific, with central value above 15 W/m2.
4. ENSO Monitoring and Outlook
Since mid-April, near-to-below average SSTs are apparent in the equatorial eastern Pacific, and the below-average subsurface temperatures in the equatorial Pacific have steadily extended to the surface, near average OLR prevails over the equatorial Pacific. Recently, the below-average subsurface temperatures have weakened slightly near the surface in the eastern Pacific, and above-average SSTs remain near the Date Line.
Based on the current monitoring of the atmosphere-ocean condition, and the predictions of dynamical/statistical climate models, equatorial central and eastern Pacific is expected to turn into a La Nina phase in the mid-late summer 2016.
We will closely monitor the development of ENSO conditions and update the ENSO wrap-up in time.