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This report provides an overview of the recent evolution and current conditions of the Asian-Australian Monsoon system. It includes rainfall patterns over the past 90 days, 30 days, and 5 days, as well as atmospheric circulation patterns and model forecasts. The summary indicates that the monsoon circulation will be near or slightly below normal for the next two weeks, except for the Southeast Asian region which will be stronger than normal.
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The Asian-Australian Monsoon System: Recent Evolution, Current Status and Prediction Update prepared by Climate Prediction Center / NCEP 1 June 2009 For more information, visit:http://www.cpc.ncep.noaa.gov/products/Global_Monsoons/Asian_Monsoons/Asian_Monsoons.shtml
Outline • Recent Evolution and Current Conditions • Monsoon Prediction • Summary • Climatology
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 the extratropical northwestern Pacific southeast of Japan. Below-normal precipitation was observed over eastern Africa, the Middle East, equatorial and southern India Ocean, southern China, southern Japan, and Australia.
Rainfall Patterns: Last 30 Days During the past 30 days, above-normal precipitation was mainly observed over Bangladesh, the Bay of Bengal, the South China Sea, the Philippines, the Philippine Sea, south of Java, and the Arafura Sea. Below-normal precipitation appeared clearly over eastern Africa, Madagascar, the Indian Ocean, East Asia, the East China Sea, Indonesia, New Guinea, and Australia.
Rainfall Patterns: Last 5 Days Above-average rainfall was observed over the eastern Bay of Bengal and subtropical northeastern Pacific last week. The rainfall over the tropical Indian Ocean and East Asia was below normal.
Rainfall Time Seriesover 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: The rainfall over the Indo-China peninsula has been mostly above normal during this rainy season. • Middle panel: The rainfall over southern India has been mostly above normal since the onset of the regional monsoon late last month. • Bottom panel: As heavy monsoon rainfall shifts northward, below-normal rainfall was observed over Indonesia and some equatorial regions.
Atmospheric Circulation The Somali jet and the cross-equatorial flow over the Indian Ocean were stronger than normal. Anomalous cyclonic patterns were observed over the Bay of Bengal, the South China Sea, and the extratropical northwestern Pacific, respectively.
NCEP/GFS Model Forecasts Bias-Corrected Precip. Anom. for Week 1 & Week 2 Week-1 Week-2
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. The NCEP Global Forecast System predicts that the large-scale monsoon circulation over tropical Asia will be near or below normal in the next two weeks. 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.
Prediction of South Asian Monsoon Circulation Upper panel: South Asian monsoon index (Goswami et al. 1999) defined as V850-V200 over 10-30ºN, 70-110ºE.Positive (negative) values indicate strong (weak) than normal monsoon. The NCEP Global Forecast System predicts that the South Asian monsoon circulation will be near normal in the next two weeks. Lower panel: Correlation between rainfall and South Asian monsoon index (Goswami et al. 1999; 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.
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. The NCEP Global Forecast System predicts that, in the next two weeks, the EAWNP monsoon circulation will be stronger than normal. 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.
Summary • Above-average rainfall was observed over the eastern Bay of Bengal and subtropical northeastern Pacific last week. The rainfall over the tropical Indian Ocean and East Asia was below normal. • The NCEP Global Forecast System predicts that, in the next two weeks, the large-scale Asian monsoon circulation (measured by the Webster-Yang monsoon index) and the South Asian monsoon circulation will be near or slightly below normal. However, the Southeast Asian monsoon circulation will be stronger than normal.
