Monthly Highlights

Climate in China

During May, monthly mean surface air temperatures were observed 1-2^oC below normal in northeastern Inner Mongolia and most of Heilongjiang. Temperatures were observed near or above normal in the other regions. In western South China and eastern Southwest China, temperatures were found 2-4^oC above normal. For the month, precipitations were found 50-80% below average in southwestern and southeastern Tibet, Yunnan and northeastern Xinjiang. Meanwhile, precipitations were observed near or more than average in the other regions, with more than 50% above average in most of Northwest China, most of Inner Mongolia, most of Northeast China, mid-northern North China and Jiangnan, and even more than 200% above average in local regions.

Climate in the World

During May, monthly mean surface air temperatures were observed more than 2^oC above normal in most of Russia, Central Asia, northwestern Africa, western Australia and northwestern North America, with about 4-6^oC above normal in parts of northern Russia and northwestern Africa. Meanwhile, temperatures were observed near or below normal in the other regions, with more than 1^oC below normal in eastern United States, northern South Asia, northeastern China and most of Japan.

For the month, precipitations were observed more than 50% above average in northern Europe, central and northern East Asia, parts of West Africa, eastern South America, western United States and Alaska, with more than 200% above average in local regions. Meanwhile, precipitations were found more than 50% below average in central Russia, West Asia, most of South Asia, western North Africa, most of Australia and western South America, with no precipitation in mid-northern Australia and along the coast of Arabian Sea.

General Circulation Features

Northern Hemisphere: During May, the mean 500hPa geopotential height field exhibited a 4-wave pattern at the mid-high latitudes. In the height anomaly field, negative anomalies dominated Scandinavian Peninsula, the Norwegian Sea, eastern North America and the eastern North Pacific. Meanwhile, heights in the other regions were observed near or above normal, with central values above 12 dam over regions from the northwestern North Atlantic to northeastern North America. The Northwest Pacific subtropical high was larger, stronger and extended remarkably westward than normal.

Southern Hemisphere: For the month, the mean 500hPa geopotential height field showed a 4-wave pattern at the mid-high latitudes. Negative anomalies below -4 dam covered southern South America and the nearby sea and the southern South Indian Ocean. Meanwhile, heights in the other regions were observed near or above normal, with the positive center values above 12 dam over the South Pole.

Tropical Features

Sea Surface Temperatures (SSTs): During May, positive SST anomalies dominated most of the equatorial Pacific and Indian Ocean, with above 0.5^oC positive SST anomalies in parts of the equatorial Pacific and Indian Ocean. The SSTA indices of NINO Z, NINO3 and NINO3.4 were all 0.4^oC, NINO1+2 and NINO4 were 0.1^oC and 0.5^oC, respectively.

Subsurface Temperatures: Compared with last month, the abnormally warm water weakened notably in the eastern equatorial Pacific, and the abnormally cold water in the offshore of South America weakened distinctly. Moreover, the abnormally warm water increased slightly in the western equatorial Pacific.

Warm Pools: During May, the area of the western equatorial Pacific warm pool was near normal and the area of the equatorial Indian Ocean warm pool was found larger than normal, and their intensities were both stronger than normal.

Wind Field: During May, at the lower troposphere (850hPa), westerly anomalies above 2m/s controlled the eastern equatorial Pacific and weak easterly anomalies controlled the eastern equatorial Indian Ocean. At the upper troposphere (200hPa), westerly anomalies above 4m/s controlled the western equatorial Indian Ocean and easterly anomalies controlled the eastern equatorial Pacific.

Southern Oscillation: During May, the Southern Oscillation Index (SOI) was -1.1, with a decrease of 0.5 compared with last month.

Convection over the Tropics: For the month, the anomalous outgoing longwave radiation (OLR) distribution exhibited that convections were suppressed over Indonesia. In the lower troposphere (850hPa) divergent wind field, a convergent center was found near 145°E, 5°N and a divergent center was observed near 90ºW, 16^oS. Correspondingly, at the upper troposphere (200hPa), a divergent center was found near 160°E, 3°S and a convergent center was observed near 90ºW, 20°S.

ENSO Monitoring and Forecasting

(1) During May, positive SST anomalies about 0.5^oC dominated the eastern and central equatorial Pacific. The SSTA indices of NINO Z, NINO3 and NINO3.4 were all 0.4^oC.

(2) During May, the abnormally warm water weakened notably in the eastern equatorial Pacific, and the abnormally cold water in the offshore of South America weakened distinctly.

(3) During May, the Southern Oscillation Index (SOI) was -1.1.

(4) At the lower troposphere (850hPa), westerly anomalies controlled the eastern equatorial Pacific.

(5) Statistical and dynamic models of BCC show that the SSTA index of NINO3 tends to be normal.

Recent tropical oceanic and atmospheric status showed that ENSO-neutral conditions remained. The evolution is going to be monitored.