Monthly Highlights

1.Climate in China

During May, monthly mean surface air temperatures were near or above normal in China, with temperatures 1-2℃ above normal in most of Northeast China and eastern Inner Mongolia, western Xinjiang, western Tibet, the middle valley of the Yangtze River, western and central Shaanxi and Ningxia, with 2-4℃ above normal in parts of above regions. Meanwhile, temperatures were found 1-2℃ below normal in central Yunnan. For the month, precipitations were found more than or near normal in most of China, with 30-100% more than average in the North, most of the Northwest, the central and western Southwest and the coast of Southeast China, with 100-200% more than normal in parts of above regions. Meanwhile, the precipitations were found 30-80% below average in most of Northeast China and eastern Inner Mongolia, western Xinjiang and central Qinghai. 

2.Climate in the World

During May, monthly mean surface air temperatures were observed 2-4℃ above normal in northern Europe, northern West Africa, West Asia, the lower valley of the Lena River in Russia, northern Northeast China, southwest America and southeast Canada, while the temperatures were near or below normal in other regions of the world, with 1-2℃ below normal in most of Mongolia, most of Australia, South Africa, western and central-south South America.

For the month, precipitations were observed more than 50% above average in eastern and northern Europe, from South Asia to the Baikal Lake, the Far East of Russia, western and southern Africa, central and southern Canada and eastern Brazil, with 100-200% above average in parts of above regions. Meanwhile, precipitations were observed more than 30% below average in regions from northeast Africa to the central Russia, from Northeast China to the Lena River in Russia, most of Australia, most of America, central-western and southern South America, with no precipitation in parts of them.

3.General Circulation Features

Northern Hemisphere: During May, the mean 500hPa geopotential height field exhibited a 5-wave pattern at the mid-high latitudes. Zonal circulation prevailed over Asia. In the height anomaly field, the northeastern North Atlantic Ocean, eastern America and the central-eastern Northwest Pacific were covered by negative height anomalies below -4 dam. Meanwhile, the Mediterranean Sea, the northern North Pacific and northeastern North America were covered by positive height anomalies between 4-8 dam, with central values above 12 dam. For the month, the Northwest Pacific subtropical high was larger and stronger than normal remarkably, and the position of its ridge line was north to normal and extended more westward than normal.

Southern Hemisphere: For the month, in the mean 500hPa geopotential height field, the mid-high latitudes were dominated by zonal circulation in the eastern hemisphere and meridional circulation in the western hemisphere. In the height anomaly field, negative anomalies below -4 dam covered the region from Antarctica to the southeastern South Pacific, with central values below -12 dam in the polar region. Meanwhile, the southern South Pacific and the southern South America were covered by positive anomalies above 4 dam.

4. Tropical Features

Sea Surface Temperatures (SSTs): During May, above 0.5℃ SST anomalies were observed in the eastern equatorial Indian Ocean and part of the western equatorial Pacific. While SSTa between -0.5~-1.5℃ covered the equatorial offshore of South America, SSTs was near normal in the remainder of the equatorial Pacific. The indices of NINO Z and NINO 3 were both 0℃, with increases of 0.2℃ from last month, NINO 1+2, NINO 4 and NINO 3.4 were -0.5℃, 0.3℃ and 0.1℃ respectively, with increases of 0.9℃, 0.3℃ and 0.2℃ from last month.

Subsurface Temperatures: During May, the abnormally cold water almost disappeared in the eastern equatorial Pacific and its remainder located in the offshore of South America. The abnormally warm water in the central-western equatorial Pacific extended eastward, and 1.0℃ anomalies extended to 110ºW.

Warm Pools: During May, the areas of the western Pacific warm pool and the Indian Ocean warm pool were larger than normal, and their intensities were stronger than normal.

Wind Field: During May, at the lower troposphere (850hPa), weak westerly anomalies controlled the eastern equatorial Pacific, while the weak easterly anomalies covered the equatorial Pacific between 150ºE-170ºW. At the upper troposphere (200hPa), the equatorial Pacific and the equatorial Indian Ocean were controlled by weak easterly anomalies and weak westerly anomalies respectively.

Southern Oscillation: During May, the Southern Oscillation Index (SOI) was -0.7, with a decrease of 1.7 since last month.

Convection over the Tropics: During May, the anomalous outgoing long wave radiation (OLR) field exhibited that convections were suppressed over the western equatorial Pacific and most of the Indian Ocean, and convections were near normal in the eastern equatorial Pacific. At the lower troposphere (850hPa) divergent wind field, a convergent center was over 100-130ºE, 10°N, and a divergent center was over 100ºW, 10°S. Correspondingly, at the upper troposphere (200hPa), a divergent center was found near 115°E, 10°N, and a convergent center was observed near 100ºW, 15ºS.

5. ENSO Monitoring and Forecasting

①During May, SSTs were near normal in the central-eastern equatorial Pacific, while SSTs remained colder than normal in region NINO 1+2.

② The Southern Oscillation Index (SOI) was -0.7, with a decrease of 1.7 since last month.

③The abnormally cold water almost disappeared in the eastern equatorial Pacific, and the abnormally warm water in the central-western equatorial Pacific extended eastward.

④The zonal winds were near normal at 850hPa and 200hPa over the equatorial Pacific.

⑤Most of ENSO forecast models indicated that SSTs will be close to normal in the central-eastern equatorial Pacific in the following 1-3 months.

In conclusion, tropical oceanic conditions showed neutral situation. The evolution of this situation will continue to be carefully monitored.