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The Asian-Australian Monsoon System: Recent Evolution,
Current Status and Prediction
Update prepared byClimate Prediction Center / NCEP
26 May 2009
For more information, visit:
http://www.cpc.ncep.noaa.gov/products/Global_Monsoons/Asian_Monsoons/Asian_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, above-normal precipitation mainly occurred over the region of 10S-20N/100-150E (except Indonesia), the Bay of Bengal, the Coral Sea, and extratropical northwestern Pacific. Below-normal precipitation was observed over eastern Africa, the Middle East, equatorial and southern India Ocean, southern China, southern Japan, and Australia.
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Rainfall Patterns: Last 30 Days
During the past 30 days, above-normal precipitation was mainly observed over the South China Sea, the Philippines, the Philippine Sea, the Bay of Bengal, south of Java, and the Arafura Sea. Below-normal precipitation was clearly observed over eastern Africa, the Indian Ocean, East Asia, Indonesia, New Guinea, and Australia.
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Rainfall Patterns: Last 5 Days
Above-average rainfall was observed over the southern Arabian Sea, Bay of Bengal, northern South China Sea, Bangladesh, and southern China last week. The rainfall over the tropical Indian Ocean, the maritime continent, Indo-China peninsula, and northwestern Pacific was overall below normal.
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Rainfall Time Series over 5x5 lat-lon boxes
*This unified land-only daily precipitation dataset is different from the CMAP dataset used in the previous three spatial maps.
• Upper panel: Heavy rainfall occurred over southern China, offsetting the dry condition in the past months.
• Middle panel: The rainfall over southeastern Indo-China peninsula has been mostly above average during the past months.
• Bottom panel: Cyclone Aila has brought heavy rainfall to South Asia including Bangladesh and eastern India, offsetting the previous dry conditions.
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Atmospheric Circulation
The monsoon circulation patterns over the western portion (the Somali jet, the cross-equatorial flow over western-central Indian Ocean, the westerly flow over southern Arabian Sea, and the cyclonic pattern over the Bay of Bengal) were stronger than normal. Anomalous cyclonic and anti-cyclonic patterns were observed over the South China Sea and the East China Sea, respectively.
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NCEP/GFS Model Forecasts Bias-Corrected Precip. Anom. for Week 1 & Week 2
Week-1
Week-2
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Prediction of Large-Scale Monsoon Circulation
Upper panel: Webster-Yang monsoon index (Webster and Yang 1992) defined as U850 (0-20ºN, 40-110ºE) – U200 (0-20ºN, 40-110ºE). Positive (negative) values indicate strong (weak) than normal monsoon.
Lower panel: Correlation between rainfall and Webster-Yang monsoon index (Webster and Yang 1992; shading) and regression of 850-mb winds on the monsoon index (vectors) for June. Green (brown) shading indicates increase (decrease) in rainfall associated with strong monsoon.
The NCEP Global Forecast System predicts that the large-scale monsoon circulation over tropical Asia will be near normal in the next two weeks.
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Prediction of East Asia – NW Pacific Monsoon
Upper panel: East Asia – Western North Pacific (EAWNP) monsoon index (Wang et al. 2008) defined as U850 (5-15ºN, 40-80ºE) – U850 (20-30ºN, 70-90ºE). Positive (negative) values indicate strong (weak) than normal monsoon.
Lower panel: Correlation between rainfall and East Asia – Western North Pacific monsoon index (Wang et al. 2008; shading) and regression of 850-mb winds on the monsoon index (vectors) for June. Green (brown) shading indicates increase (decrease) in rainfall associated with strong monsoon.
The NCEP Global Forecast System predicts that, in the next two weeks, the EAWNP monsoon circulation will be stronger than normal.
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Summary
• Above-average rainfall was observed over the southern Arabian Sea, Bay of Bengal, northern South China Sea, Bangladesh, and southern China last week. The rainfall over the tropical Indian Ocean, the maritime continent, Indo-China peninsula, and northwestern Pacific was overall below normal.
• The NCEP Global Forecast System predicts that the Southeast Asian monsoon circulation will be stronger than normal in the next two weeks, in spite of near normal large-scale monsoon circulation over tropical Asia.
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Onset of the Asian MonsoonOnset of the Asian Monsoon
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ClimatologyClimatology
