Monthly highlights

1.Climate in China

During　September, averaged temperature in China was the highest at the same time since 1961. Monthly mean surface air temperatures were about 2~4℃ above normal in northwestern Northeast China, southern Jiangsu, Zhejiang, northern Fujian, northern Jiangxi, southern Anhui, southeastern Hubei, middle reaches of the Yangtze River, most of Xinjiang. For the month, precipitations were 30~200% above normal in the southern of North China, regions between low reaches of the Yellow River and the Yangtze River, eastern Northwest China, Hainan, northern Jiangxi, the western Tibetan Plateau. Precipitations were near or below normal in the rest areas, with 30~80% below normal in central and eastern Inner Mongolia, southern and eastern Northeast China, western Zhejiang, northern Fujian, western Hunan, northern Guangxi, eastern Guizhou, central Sichuan, most of Northwestern China, and no rainfall was observed in local of above regions.

2. Climate in the World

During September, temperatures were about 1~2℃ below normal in the central South America, western shore of U.S.A, western shore of Australia, western Mongolia. Meanwhile temperatures were near or above normal in the rest areas, with 2~3℃above normal in the East European Plain, the Plat of Iran, the West Siberian, parts of eastern China, central and northeastern U.S.A, central Australia.

During September, total rainfall was more than 50% above normal in southeastern European, most of West Africa and South Asia, the central Indochina Peninsula, central-eastern China, western Alaska, southern Brazil, southwestern Mexico, southeastern 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 eastern European, southern Africa, northwestern Australia, middle Asia, Northeast China and South China, Russia’s Far East region, eastern and western U.S.A, northeastern Brazil.

During September, major weather and climate events in the world are ：

• Typhoon Nabi attacked western Japan

• Typhoon Talim and Khanun attacked southeastern China

• Heavy rainfall produced landslides in western Indonesia

• Severe storm attacked the Bay of Bengal

• Hurricane Ophelia attacked eastern U.S.A

• Typhoon Damrey attacked Philippines, China and Vietnam

• Consecutive rainfall led to floods in western India and western Nepal

• Hurricane Rita attacked southern U.S.A

• Heavy rain attacked southern and eastern Romania

3. General Circulation Features

Northern Hemisphere: During September, in the 500hPa height anomaly field, positive anomalies above 4 dam dominated the regions around central-northern Europe, northern East Asian, the Aleutian Islands, central and eastern North America, with maximums above 8 dam. Meanwhile, negative anomalies below -4 dam were observed over the Greenland Sea and the Barents Sea, part of Russia’s Far East region, south-western of Canada. For the month, the Northwest Pacific subtropical high was stronger than normal and extended westward compared with normal position.

Southern Hemisphere: During September, the mean 500hPa geopotential height field exhibited a 3-wave pattern at the mid-high latitudes. In the height anomaly field, negative anomalies below -4 dam covered the oceans to the south of Africa and southwest of Australia, and the Ross Sea, with center value below -12 dam. Meanwhile, heights were near or more than 4 dam above normal over the rest of the mid-high latitudes, with maximums above 12 dam over the South Shetland Island.

4. Tropical Features

Sea Surface Temperatures (SSTs): During September, SST anomalies below -0.5℃ were observed in the eastern equatorial Pacific and the offshore of South America, near or above normal SST dominated the rest of the equatorial Pacific. The indices of NINO1＋2, NINO 3, NINO3.4 and NINO Z were -0.7℃, -0.3℃, 0.0℃ and 0.1℃, with drops of 0.5℃, 0.5℃, 0.2℃, 0.2℃ from last month, respectively. The index of NINO 4 was still 0.4℃.

Subsurface Temperatures: During September, subsurface ocean temperatures were above normal in the western equatorial Pacific. Abnormally subsurface cold water in the equatorial Pacific east to 140ºW generally enhanced and cold center eastward and upward.

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

Wind Field：During September, at the lower troposphere (850hPa), zonal winds were near normal over most of the equatorial Pacific and the Indian ocean except for westerly anomalies about 2-4m/s controlled the region nearby 160°W. At the upper troposphere (200hPa), zonal winds were near normal over the equatorial Pacific and the equatorial Indian Ocean.

Southern Oscillation: During September, Southern Oscillation Index (SOI) was 0.4, and increased 0.9 from last month.

Convection over the Tropics: For the month, the anomalous outgoing longwave radiation (OLR) showed that convections were stronger than normal over the tropical western Pacific. In the lower troposphere (850hPa) divergent wind field, a convergent center was over 135ºE, 15ºN, and a divergent center was over 80ºW, 35ºS. Correspondingly, at the upper troposphere (200hPa), a convergent center and a divergent center were around 92.5ºW, 25ºS and 130ºE, 15ºN respectively.

5. ENSO Monitoring and Forecasting

①  During September, negative SST anomalies were observed in the eastern equatorial Pacific, but the index of NINO Z was 0.1℃.

②   During September, 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 0.4 in September.

④ During September, convections were stronger than normal over the western 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 September and ENSO cycle will likely be neutral in the following 3 months. The evolution will be monitored closely and continuously.