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 16 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
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 and Northeast Asia, and the subtropical
North Pacific.
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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, eastern Indian Ocean, the South China
Sea, the maritime continent (except
western-central Indonesia and Papua New Guinea),
tropical western Pacific (except the equatorial
region east of 150E), and over 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, eastern India, Bangladesh, the
coastal regions of East and Northeast Asia, and
subtropical northwestern Pacific.
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Rainfall Patterns Last 5 Days
The precipitation pattern during the last 5 days
was characterized by the heavy and above-normal
precipitation over the eastern Bay of Bengal,
western Indo-China peninsula, the South China
Sea, and the subtropical northwestern Pacific
(due to the effects of typhoon and tropical
storms). Below-normal precipitation was observed
over the tropical Indian Ocean, western-central
Indonesia, southern and eastern China, and the
east coast of Australia.
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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 Before the impact of summer monsoon,
  the rainfall over southern China remained below
  normal.
• Central-bottom right The rainfall over the
  southern Indo-China peninsula, the Philippines,
  and other northern tropical lands in the AA
  monsoon region continued to be above normal.
• While the major rain band had shifted to the
  northern tropics, the precipitation over the
  southern tropics became mainly below normal.

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Recent Evolution OLR

• Convection has been further intensifying over the
  South China Sea and most of the (central-eastern)
  maritime continent.
• Convection has becoming weaker over the eastern
  Bay of Bengal and western Indo-China peninsula
  and has been further suppressed over the tropical
  western-central Indian Ocean and Australia.
• Convection has become weaker and been suppressed
  over East Asia including southern and eastern
  China.

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Atmospheric Circulation 200 mb

• Compared to the last week (left panel), the
  upper-level anomalous anti-cyclonic pattern over
  southern Asia and the easterly anomalies over its
  southern flank and over the Arabian Sea have
  become stronger, favoring an earlier
  establishment of large-scale Asian summer monsoon
  circulation.

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Atmospheric Circulation 850 mb

• Lower-level westerlies have extended eastward
  from the Bay of Bengal and the Indo-China
  peninsula to the South China Sea (SCS) and the
  Philippine Sea.
• Westerlies have prevailed over the central SCS
  and anomalous westerly flow has clearly appeared
  and intensified over southern-central SCS (right
  panel), favoring an early onset of the SCS summer
  monsoon.
• Northward cross-equatorial flow continues to be
  stronger than normal over the Indian Ocean.

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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 normal or stronger than
  normal, implying normal or above normal
  precipitation and lower-level westerly anomalies
  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 be close to
  normal in the next two weeks.

• 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 western North
  Pacific will be normal or stronger than normal,
  meaning normal or above 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 southern
  East Asia during the past several days.
• Lower-level westerlies have prevailed over the
  Indo-China peninsula and southern-central South
  China Sea, favoring an early onset of the South
  China Sea summer monsoon.
• The NCEP Global Forecast System predicts that the
  large-scale Asian monsoon circulation and the
  monsoon over East Asia and western North Pacific
  will be near normal or stronger than normal in
  the coming two weeks. It also predicts
  near-normal monsoon circulation over South Asia.

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Onset Dates of ASM
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Climatology