The AsianAustralian Monsoon System: Recent Evolution, Current Status and Prediction

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The Asian-Australian Monsoon System Recent
Evolution, Current Status and Prediction
Update prepared by Climate Prediction Center /
NCEP 23 May 2008
For more information, visit http//www.cpc.ncep.
noaa.gov/products/Global_Monsoons/Asian_Monsoons/A
sian_Monsoons.shtml
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Outline

• Recent Evolution and Current Conditions
• Monsoon Prediction
• Summary
• Climatology

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Rainfall Patterns Last 90 Days
During the past 90 days, heavy precipitation
occurred over much of the maritime continent,
tropical eastern Indian Ocean, tropical western
and southwestern Pacific, and the North Pacific
storm-track region. Precipitation was above
normal over most of the tropics except the
below-normal rainfall over the western Indian
Ocean, Papua New Guinea, and the equatorial
Pacific east of 145E. Above-normal precipitation
also appeared over the storm-track region.
Below-normal precipitation was found over the
subtropical Southern Hemisphere including
Madagascar, the Indian Ocean, and Australia.
Precipitation was also below normal over the
Middle East, western Asia, the coastal regions of
East Asia, and the subtropical North Pacific high
area.
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Rainfall Patterns Last 30 Days
Heavy precipitation occurred over the tropics and
the North Pacific storm-track region.
Precipitation was above normal over the Bay of
Bengal, the South China Sea, the maritime
continent (except the dry conditions over western
Indonesia and Papua New Guinea), tropical western
Pacific (except the equatorial region east of
150E), and the storm-track region. Below-normal
precipitation was found over much of the Southern
Hemisphere including Madagascar, the Indian
Ocean, and Australia. Precipitation was also
below normal over the Middle East, western Asia,
southeastern India, Bangladesh, the coastal
regions of East Asia, and the subtropical
northwestern Pacific high area.
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Rainfall Patterns Last 5 Days
The precipitation pattern during the last 5 days
was characterized by the large rainfall over the
northern tropics and subtropics east of 90E and
over the northwestern Indian Ocean. Above-normal
precipitation was over the central South China
Sea and the subtropical northwestern Pacific.
However, below-normal precipitation appeared over
much of the tropical Indian Ocean, southern
maritime continent, the northeast coast of
Australia, and eastern China.
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Recent Evolution Rainfall
For other boxes, see http//www.cpc.ncep.noaa.gov
/products/ Global_Monsoons/Asian_Monsoons/90d-prec
ip_click_map.shtml

• Upper right The rainfall over southwestern China
  including Sichuan Province has been continuously
  over normal during this rainy season in spite of
  a decrease in the recent days.
• Central right The monsoonal rainfall over the
  Indo-China peninsula, central South China Sea,
  and the Philippines has been mostly near normal
  or above normal.
• Bottom right The rainfall over southern India
  had been below normal however, the recent
  increase in the local rainfall should be further
  monitored.

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Recent Evolution OLR

• Convection has been weakening over the Indo-China
  peninsula, the South China Sea, and the
  Philippine Sea but was still above normal.
• Over southern China, normal convection returned
  and the influence of monsoon should be monitored.
• While convection remained weak over the tropical
  Indian Ocean and Australia, it intensified over
  the western Arabian Sea.
• Convection has become active over the western
  South Indian Ocean after the long-lasting dry
  conditions.

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Atmospheric Circulation

• Left The upper-level westerlies over the
  tropical western South Indian Ocean (IO) have
  intensified significantly, and weak easterly
  anomalies still remained over the northern
  tropics.
• Right The southeasterly trade wind over the
  tropical IO, the cross-equatorial flow over
  western IO, and the low-level westerlies
  extending from the Arabian Sea, the Bay of
  Bengal, the South China Sea, and the western
  Pacific remained stronger than normal.
• Right The anomalous low-level northeasterly
  wind over southern China has become weaker
  compared to last week, accompanied by increasing
  rainfall.

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W-Y Monsoon Prediction

• Upper panel Webster-Yang monsoon index (Webster
  and Yang 1992) defined as the mean U850-U200 over
  0-20N, 40-110E. The NCEP GFS predicts that, in
  the next two weeks, the large-scale monsoon
  circulation will be near normal, implying near
  normal precipitation and lower-level westerlies
  over tropical Asia including the Indo-China
  peninsula and the South China Sea.

• Lower panel Correlation between precipitation
  and the Webster-Yang monsoon index (Webster and
  Yang 1992 shading) and regression of 850-mb
  winds against the monsoon index (vectors) for May.

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SA Monsoon Prediction

• Upper panel South Asian monsoon index (Goswami
  et al. 1999) defined as the mean V850-V200 over
  10-30N, 70-110E. The NCEP GFS predicts that the
  South Asian monsoon circulation will continue to
  be near normal in the next week and tend to be
  stronger afterwards.

• Lower panel Correlation between precipitation
  and the South Asian monsoon index (Goswami et al.
  1999 shading) and regression of 850-mb winds
  against the monsoon index (vectors) for May.

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EA-WNP Monsoon Prediction

• Upper panel East Asian Western North Pacific
  monsoon index (Wang et al. 2008) defined as the
  mean difference of U850(5-15N/90-130E)
  U850(20-30N/110-140E). The NCEP GFS predicts
  that, in the next two weeks, the monsoon
  circulation over East Asia and the western North
  Pacific will be normal or weaker than normal,
  meaning normal or below normal precipitation over
  the northern maritime continent and tropical
  northwestern Pacific.

• Lower panel Correlation between precipitation
  and the East Asian Western North Pacific
  monsoon index (Wang et al. 2008 shading) and
  regression of 850-mb winds against the monsoon
  index (vectors) for May.

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Summary

• Above-normal precipitation occurred over most of
  the tropical Asian-Australian region during the
  past months except over the equatorial western
  Pacific (east of 145E) and the tropical western
  Indian Ocean. Above-normal precipitation was also
  found over the subtropical western Pacific
  storm-track region.
• Below-normal precipitation appeared over the
  subtropical southern Indian Ocean, Madagascar,
  Australia, and the subtropical northwestern
  Pacific high region. The Middle East and western
  Asia were also drier than normal during the past
  months.
• While major rain belt had shifted to the northern
  tropics, the precipitation over the southern
  tropics appeared below normal. Below-normal
  precipitation was also observed over some East
  Asia regions.
• The low-level westerlies over tropical Asia have
  been stronger than normal and monsoon rain band
  has further extended northward to northern South
  China Sea. Rainfall tends to increase over
  southern China.
• The NCEP Global Forecast System predicts that the
  Asian monsoon will be largely near normal in the
  coming two weeks.

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Onset Dates of ASM
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Climatology