1. Climate in China

In April 2016, the surface air temperature averaged over China was 12.6ºC, with 1.6ºC above normal (11.0ºC), ranking the 2nd highest since 1951. The mean precipitation was 62.2mm over China, which was 39.2% above normal (44.7mm), ranking the 4th most since 1961. For the month, extremes of Daily Temperature Drop (DTD) and heavy precipitation were observed in China.

2. General Circulation Features

Northern Hemisphere: During April 2016, in the field of mean 500hPa geopotential height anomaly, positive anomalies above 4 dam covered the northern Atlantic Ocean, the Ural Mountain, and the region from the northern North Pacific to the Arctic. Meanwhile, negative anomalies below -4 dam covered the region from the eastern Atlantic Ocean to Europe and the northern North Pacific, with the central value below -12dam over the northern North Pacific. During the month, the northwestern Pacific subtropical high was stronger than normal, with the area larger than normal. The western point of its extended ridge shifted further westward than normal.

Southern Hemisphere: For the month, in the field of mean 500hPa geopotential height anomaly, the positive anomalies over 4 dam were observed over the region from Bellingshausen Sea to Amundsen Sea, with the central value below 12 dam over the Amundsen Sea. Meanwhile, the negative anomalies below -4 dam covered the southwestern Pacific and southern Indian Ocean.

3. Tropical Features

Sea Surface Temperatures (SSTs): In April 2016, SSTs were over 0.5℃ above normal in most of the central and eastern equatorial Pacific, with central values 1.5-2.0℃ above normal. Indices of Nino1+2，Nino3，Nino4，Nino3.4 and Nino Z were 0.8℃，1.0℃，0.8℃，1.1℃ and 0.9℃, respectively. The Indian Ocean Basin-Wide SSTA variation index (IOBW) was 0.8. 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 westerly anomalies dominated over most of the central-eastern equatorial Pacific, while the easterly anomalies dominated over the area to the north of equator over West Pacific and the region from the South China Sea to the Indian Ocean. To be noted that the easterly anomalies could be observed over the Nino1+2 zone of eastern equatorial Pacific. At upper troposphere (200hPa), the easterly anomalies prevailed over the central equatorial Pacific Ocean while the westerly anomalies dominated over the eastern equatorial pacific and the region from the western equatorial Pacific to equatorial Indian Ocean.

Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was -1.3.

Convections over the Tropics: During the month, the anomalous outgoing longwave radiation (OLR) showed that convections were active near the dateline and the region to the east of it till 160°W, with central value below -30 W/m². However, convections were suppressed to the north of equator over the West Pacific to the South China Sea, with central value above 30 W/m².

4. ENSO Monitoring and Outlook

Since mid-April, near-to-below average SSTs are apparent in the equatorial eastern Pacific, while above-average SSTs remain in the equatorial central Pacific. The below-average subsurface temperatures in the equatorial Pacific have steadily extended to the surface. Accompanied with the cold Kelvin waves in the equatorial Pacific propagating eastward, the El Niño event will further weaken. The anomalies of both tropical atmospheric and oceanic circulation are well coupled and show a clear El Niño-South Oscillation pattern, but since mid-March, the negative anomalies of outgoing longwave radiation (OLR) have disappeared over the equatorial eastern Pacific.

Based on the current monitoring of the atmosphere-ocean condition, and the predictions of dynamical/statistical climate models, the present El Niño event should be further to decay and be likely to end in May 2016. Subsequently, equatorial central and eastern Pacific is expected to turn into a La Niña phase in the following summer.

We will closely monitor the development of ENSO conditions and update the ENSO wrap-up in time.