During September, monthly mean surface air temperatures were near or
above normal in most of China, with about 1-2℃ above average in Northeast China,
eastern Inner Mongolia, southern Xinjiang and most of the Tibetan plateau, even
more than 2℃
above average in the part of areas. In this month, rainfall totals were
30-100% more than normal in eastern North China, most of Inner Mongolia,
northern XinJiang, southwestern Yunnan, southern Shanxi, the northeastern
Sichuan Basin, western Henan, southern Zhejiang and eastern Fujian. Meanwhile,
rainfall totals were 30-100% below normal in most of Northeast China, western
North China, the mid-lower reaches of the Yangtze River, Guangxi, western
Guangdong, central Gansu and most of Xinjiang and the Tibetan plateau.
Monthly mean surface air temperatures were 1-3℃
less than average in northwestern North America, central-northern Africa,
central-northern Australia. Meanwhile temperatures were near or above normal in
the rest of world, with about 2-4℃ above average in parts of northwestern Russia and East Siberia,
Kazakhstan, the central-northern USA and central South America.
For the month, rainfall totals were
50-200% more than normal in most of
Northern Europe, parts of Siberia and eastern China, the western Indo-China
Peninsula, the eastern and central-western USA, northern Mexico and the
Caribbean coast of South America, and even several times more than normal
locally. Rainfall totals were about 50-100% less than normal in much of Europe,
western Asia, northwestern Africa, western and the central-eastern USA, most
South America and northern Australia.
Northern Hemisphere:
At the mean 500hPa geopotential height field in
September, the polar vortex was slightly weaker than normal and zonal
circulation prevailed over the mid-high latitudes. In the height anomaly field,
the areas from Northern Europe to Siberia and northwestern North America were
covered by negative anomalies, with values below –4 dam over North America.
Meanwhile, most of the other regions in the mid-high latitudes were dominated by
positive anomalies, with the center values above 8 dam over the central-northern
Pacific and central-eastern North America. The Northwest Pacific subtropical
high was larger and stronger than normal, and its position
expanded westward obviously.
Southern Hemisphere: In this month, the mean 500hPa geopotential height
field exhibited a 3-wave pattern at the mid-high latitudes. Negative anomalies
below –4 dam covered southwestern Atlantic and the part regions south to
Australia. Meanwhile, heights in the other regions were near or above normal.
Positive departures above 8 dam covered much of the polar region, with center
values above 16 dam.
Sea
Surface Temperatures (SSTs): During September, above 0.5℃
SST anomalies still maintained in the central equatorial Pacific, with center
values above 1.5℃.
SSTs in the eastern equatorial Pacific increased remarkably and weak positive
SST anomalies were observed in much of regions. Meanwhile, below -0.5℃
SST anomalies remained in the area nearby Peru. Correspondingly, the SST indices
of NINO 4, NINO 3, NINO 1+2 and NINO Z were 1.1℃, 0.3℃, -0.4℃and 0.6℃,
respectively. SSTs in the western equatorial Pacific and the
equatorial Indian Ocean were slightly higher than normal.
Subsurface
Temperatures: During
September, the negative anomalies nearby South America in the equatorial Pacific
weakened obviously. The abnormally warm water was strengthen remarkably in the
central equatorial Pacific, with values above 3℃ in the area between 140°W to 170°W.
Warm
Pools: In
September, the western equatorial Pacific warm pool was slightly larger than
normal, with its intensity increasing compared with that of last month. The
equatorial Indian Ocean warm pool was near normal.
Southern
Oscillation:
During September, the Southern Oscillation Index was –0.3.
Convection
over the Tropics: During the month, the anomalous outgoing longwave
radiation (OLR) distribution exhibited that convections were stronger than
normal over the western equatorial Pacific and near normal over the central and
eastern equatorial Pacific. In the lower troposphere (850hPa) divergent wind
field, the convergent center was over 140°E, 10°N, and the divergent center was around 75°W, 25°S. Correspondingly, the divergent center at
the upper troposphere (200hPa) was over 150°E in the equator, and the convergent center was over 125°W, 15°S.
a)
Positive
SST anomalies kept rose in the central equatorial Pacific and expanded eastward
during September. At the same time, SST increased rapidly in the eastern
equatorial Pacific and weak positive anomalies dominated much of the region.
b)
In
this month, abnormally cold water nearby South America in the equatorial Pacific
was weakened remarkably. Abnormally warm water was strengthen obviously and
positive temperature anomalies above 3℃ appeared in the central
equatorial Pacific.
c)
The
Southern Oscillation Index kept negative.
d)
At
the lower troposphere (850hPa), westerly anomalies controlled most of the
equatorial Pacific.
e)
The convections were activity over the western equatorial Pacific and near
normal over the central and eastern equatorial Pacific.
f) Most of statistical models forecasts indicated near neutral conditions of the Nino3 SSTA sustained for the next 3-6 months.
Recent oceanic and atmospheric conditions in
the tropical Pacific
showed the characteristic of El Nino. SSTs are expected further
increase
in the
central and eastern equatorial Pacific and ENSO warm-episode will persist for
next 2-3 months.