Monthly Highlights

1. Climate in China

During October, Monthly mean surface air temperatures were about 2~4℃ above normal in western Heilongjiang，western Jilin, central and northern Inner Mongolia. Monthly mean surface air temperatures were below normal in south of North China, east of Northwest China, east of Southwest China, western regions between the Huaihe River and the Yellow River, and west of Jianghan Region. For the month, precipitations were 30~200% above normal in eastern Northwest China, east of Tibetan plateau, eastern Yunnan, part regions of Southeast inshore. Precipitations were near or below normal in the rest areas, with 30~80% below normal in north of Northeast China, Inner Mongolia, North China, most of Huaihe river, most of Jiangnan, most of South China, south of Xinjiang and west of Tibet, and no rainfall was observed in parts of above regions.

2. Climate in the World

During October, temperatures were about 1~2℃ below normal in parts of West Asia, central and southern South America and western Australia. Meanwhile, temperatures were near or above normal in the rest areas, with 2~4℃ above normal in northern Europe, west-central and northeastern Russia, parts of central and eastern Asia, Northeast China, parts of West Africa, parts of northwestern North America, eastern South America and east-central Australia.

During October, total rainfall was more than 50% above normal in southwestern Europe, south-central and northeastern Russia, parts of West Asia, southern India, parts of western China, southern West Africa,  central and western U.S.A, eastern shore of U.S.A, northern Mexico, parts of South America and central Australia, with more than 200% above normal in parts of above regions. Precipitations were near or below normal in the remainder of the world, with 50～100% below normal in central Europe, western Russia, most of central and southern Asia, northern China, northwestern Canada, parts of east-central of U.S.A, parts of western and southern Africa and northwestern Australia.

3. General Circulation Features

Northern Hemisphere: During October, the mean 500hPa geopotential height field exhibited a 4-wave pattern at the mid-high latitudes, and the polar vortex was weaker than normal. In the 500hPa height anomaly field, positive anomalies above 4 dam dominated the regions around most of Europe, northwest of Asian, most of North Pacific, and northeastern North America, with maximums above 12 dam. Meanwhile, negative anomalies below -4 dam were observed over the eastern North Atlantic, central and eastern Russia, northwesternmost of North America and the northeastern North Pacific, with minimums below -8 dam. For the month, the Northwest Pacific subtropical high was stronger than normal and extended westward compared with normal position.

Southern Hemisphere: During October, zonal circulation prevailed over mid-high latitude in the mean 500hPa geopotential height field, negative anomalies below -4 dam covered the southern South Atlantic, the southeastern South Pacific, and the eastern South Indian Ocean. Meanwhile, heights were near or above normal over the rest of the mid-high latitudes, with maximums above 8 dam over the Ross Sea.

4. Tropical Features

Sea Surface Temperatures (SSTs): During October, SST anomalies above 0.5℃ were observed in the central and western equatorial East Pacific, and negative anomalies below -0.5℃ were observed in the eastern equatorial Pacific and the offshore of South America. Weak positive anomalies were over the equatorial Indian Ocean. The indices of NINO 1＋2 and NINO C were –1.2℃ and 0℃, with drops of 0.5℃ and 0.1℃ respectively; NINO 3, NINO 4, NINO 3.4 and NINO Z were –0.2℃, 0.5℃, 0.2℃ and 0℃, with increase of 0.1℃, 0.1℃, 0.2℃ and 0.1℃ from last month.

Subsurface Temperatures: During October, subsurface ocean temperatures were above normal in the western equatorial Pacific. Abnormally subsurface cold water in the equatorial Pacific east to 140ºW slightly enhanced.

Warm Pools: During October, the area and the intensity of the western Pacific and Indian Ocean warm pool were larger and stronger than normal, respectively.

Wind Field：During October, at the lower troposphere (850hPa), weak easterly anomalies were over the central equatorial Pacific, and weak westerly anomalies were over the western equatorial Indian Ocean. Zonal winds were near normal over the remainder regions. At the upper troposphere (200hPa), easterly anomalies were over the eastern equatorial Pacific, zonal winds were near normal over the remainder regions.

Southern Oscillation: During October, Southern Oscillation Index (SOI) was 1.4, and increased 1.0 from last month.

Convection over the Tropics: For the month, the anomalous outgoing longwave radiation (OLR) showed that convections were near normal over the tropical Pacific. In the lower troposphere (850hPa) divergent wind field, convergent centers were over 100ºE, 10ºN and 140ºE, 10ºN, and a divergent center was over 110ºW, 10ºS. Correspondingly, at the upper troposphere (200hPa), a convergent center was over 120ºW, 15ºS, and divergent centers were over 100ºE, 5ºN and 150ºE, 5ºN.

5. ENSO Monitoring and Forecasting

①   During October, negative SST anomalies were persistent in the eastern equatorial East Pacific, weak positive SST anomalies were observed in the central and western equatorial Pacific. SST indices were near normal except that NINO 1+2 was below normal.

②   During October, subsurface ocean temperatures were above normal in the western equatorial Pacific, and below normal in the eastern equatorial Pacific.

③   The Southern Oscillation Index (SOI) was 1.4 in October.

④ During October, at the lower troposphere (850hPa), weak easterly anomalies were over the central equatorial Pacific, and weak westerly anomalies were over the western equatorial Indian Ocean. Convections were near normal over the tropical Pacific.

⑤ Forecasts of most ENSO statistical models showed that SSTA index for NINO 3 will be slight negative in the following 3 months.

Above results showed that generally tropical atmospheric and oceanic conditions were near normal in October and ENSO cycle will likely be neutral in the following 3 months. The evolution will be monitored closely and continuously.