During August,
monthly mean surface air temperatures were 1-2℃ lower than normal in
central Inner Mongolia, and most of Henan and Hubei. Temperatures were around
1-2℃above average in
northeastern Inner Mongolia, eastern East China, southern Qinghai and northwestern
Sichuan. In this month, rainfall totals were 30~100% more than normal in
western and eastern XinJiang, western Qinghai, central Inner Mongolia and part
of the middle reaches of the Yangtze River. Meanwhile, in the rest of China,
rainfall totals were near or less than normal, with 30%~100% below normal in
eastern Northeast China, northeastern North China, the lower reaches of the
Yangtze River, Guangxi, western Inner Mongolia, western Tibet and southern
XinJiang.
Monthly mean
surface air temperatures were 1~2℃ above average in
western Africa, eastern Mongolia, eastern Far East of Russia, western Canada, Alaska,
eastern and northern Europe. Meanwhile temperatures were 1-2℃ less than normal
in central North America and most of Siberia, and even -4℃ below average
locally.
For the month, rainfall
totals were 50% more than normal in Kazakhstan, West Siberia, northern South
America, western Africa, and part of the three areas of eastern Europe, eastern
Russia and western North America, and even 100% more than normal locally. In
the rest of the world, rainfall totals were near or less than normal, with 50%-100%
below normal in Alaska, central South America, northern Australia and Plat of
Iran.
Northern
Hemisphere: During August, the mean 500hPa geopotential height field exhibited a 4-wave
pattern at the mid-high latitudes. In the height anomaly field, negative
anomalies dominated the northeastern Atlantic, central North America, and the
areas from the Center Siberian Plateau to the northwestern Pacific. Meanwhile,
the regions nearby the Bering Strait, the Greenland and west to the Ural
Mountains were controlled by positive anomalies, with center values above 8 dam
over the Bering Strait. The Northwest Pacific subtropical high was stronger and
larger than normal.
Southern
Hemisphere: In this month, the mean 500hPa geopotential height field exhibited a
3-wave pattern at the mid-high latitudes. Positive departures above 4 dam covered
the Antarctica, the southern and eastern South Pacific, with center values
above 24 dam over the southeastern South Pacific. Meanwhile, negative anomalies
controlled the other regions at the mid-high latitudes.
Sea Surface
Temperatures (SSTs): During August, above 0.5℃ SST anomalies
dominated the central equatorial Pacific, with center values above 1.0℃. Meanwhile,
below -0.5℃ SST anomalies
covered the eastern equatorial Pacific, but the regions controlled by negative
SST anomalies reduced and SSTs nearby 120°W enhanced obviously from
July. Weak positive SST anomalies were observed in most of the tropical Indian
Ocean. Correspondingly, the SST indices of NINO 4, NINO 3, NINO 1+2 and NINO Z
were 0.9℃, 0.1℃, -1.1℃and 0.3℃, respectively. In addition, above indices rose from last month.
Subsurface
Temperatures: Compared with that of last month, location of the positive anomalies
center in the equatorial Pacific rose and shifted eastward to nearby 140-120ºW, accompanied with
intensity of positive anomalies weakened. Meanwhile, the extent of negative
anomalies shrunk in the eastern equatorial Pacific.
Warm Pools: In this month,
the western equatorial Pacific warm pool was slightly larger than normal, with
its intensity weakening compared with that of last month. The equatorial Indian
Ocean warm pool was near normal.
Southern Oscillation: During
August, the Southern Oscillation Index was –0.6.
Convection
over the Tropics: During August, the
anomalous outgoing longwave radiation (OLR) distribution exhibited that convections
were near normal over the central and eastern equatorial Pacific; while
enhanced convection were over the areas northeast to the Philippines and
suppressed convections were over the Indonesia. In the lower troposphere
(850hPa) divergent wind field, the convergent center was over 140°E, 18°N, and the divergent center was around 105°W, 5°S. Correspondingly, the divergent center at
the upper troposphere (200hPa) was over 135°E, 15°N and the convergent centers were over 125°W, 5°S, and 125ºW,20ºN,
respectively.
a) Compared with
that of last month, SST kept rose in the central equatorial Pacific, especially
in the regions nearby 120°W. Meanwhile, SST
descended obviously in the western tropical Pacific.
b) During August,
location of positive subsurface temperature anomalies center in the central
equatorial Pacific rose and shifted eastward, accompanied with intensity weakened.
Meanwhile, the areas of negative anomalies shrunk in the eastern equatorial
Pacific.
c) The Southern
Oscillation Index was –0.6.
d) At the lower
troposphere (850hPa), westerly anomalies controlled most of the equatorial
Pacific.
e) The convections were near normal over the central and eastern equatorial
Pacific; while enhanced convections were over the areas northeast to the Philippines
and suppressed convections were over the Indonesia.
f)
Most of models forecasts indicated slightly
cold or near neutral conditions of the Nino3 SSTA sustained for the next 3
months except for the forecast of PC-CCA.
Based on above analyses, it is likely that SSTA in the central
equatorial Pacific will remain positive for the next 3 months. Current
conditions are preferable to the development of ENSO warm-episode.