The Asian-Australian Monsoon System: Recent Evolution, Current Status and Prediction

1. The Asian-Australian Monsoon System: Recent Evolution, Current Status and Prediction Update prepared by Climate Prediction Center / NCEP September 7, 2010 For more information, visit:http://www.cpc.ncep.noaa.gov/products/Global_Monsoons/Asian_Monsoons/Asian_Monsoons.shtml

2. Outline • Recent Evolution and Current Conditions • Monsoon Prediction • Summary • Climatology

3. Precip Patterns: Last 90 Days During the past 90 days, above-average rainfall was observed over much of southern Asia and tropical Indian Ocean. Above-average rainfall was also seen over East Asia, western North Pacific, and part of western Asia and the Middle East. On the contrary, below-average rainfall was observed over eastern India, southern Indo-China peninsula, and equatorial western Pacific Ocean. The rainfall over much of Indonesia, Iran, and Afghanistan was highly above normal.

4. Precip Patterns: Last 30 Days During the past 30 days, above-average rainfall occurred over the Asian monsoon region (e.g. 10S-40N, 60E-140E), with exceptions over eastern India, southern China, Japan, and southern Indo-China peninsula. The rainfall over much of Indonesia was highly above normal.

5. Precip Patterns: Last 5 Days Above-average rainfall was observed over western India, the Bay of Bengal, the South China Sea, Taiwan, Korea, the Philippine Sea, and the tropical central-eastern Indian Ocean. On the other hand, below-average rainfall was found over eastern India, Bangladesh, southern China, Japan, and the tropical western Pacific Ocean.

6. 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 Korea has been mostly above average after the Changma period. Middle panel: Southern Indo-China peninsula is one of the few regions where rainfall has been mostly below average during the summer. Lower panel : The rainfall over northern India has been quite persistently over average since the onset of the local monsoon.

7. Atmospheric Circulation The cross-equatorial flow over western-central Indian Ocean and the monsoon flow over the Arabian Sea were stronger than normal. Anomalous cyclonic patterns were observed over northern India and Bay of Bengal and over northern South China Sea. The trade wind over tropical Pacific was stronger than normal, leading to convergence over the South China Sea. In addition, substantial water vapor was transported over Korea and adjacent regions.

8. NCEP/GFS Model Forecasts Bias-Corrected Precip. Anom. for Weak 1 & Week 2 Week-1 Week-2

9. 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 Webster-Yang monsoon index will be above normal in the next two weeks after being below or near normal for the entire summer. 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 September. Green (brown) shading indicates increase (decrease) in rainfall associated with strong monsoon.

10. Prediction of South Asian Monsoon Circulation Upper panel: South Asian monsoon index (Goswami et al. 1999) defined as v850 (10-30ºN, 70-110ºE) – v200 (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 stronger than 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 September. Green (brown) shading indicates increase (decrease) in rainfall associated with strong monsoon.

11. Prediction of East Asian Monsoon Upper panel: East Asian monsoon index (Li and Zeng 2002; GRL). Positive (negative) values indicate strong (weak) than normal monsoon. The NCEP Global Forecast System predicts that, in the next two weeks, the East Asian monsoon circulation will be mainly weaker than normal. Lower panel: Correlation between rainfall and East Asian monsoon index (Li and Zeng 2002; shading) and regression of 850-mb winds on the monsoon index (vectors) for September Green (brown) shading indicates increase (decrease) in rainfall associated with strong monsoon.

12. 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 monsoon circulation over Southeast Asia and northwestern Pacific will be weaker 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 September Green (brown) shading indicates increase (decrease) in rainfall associated with strong monsoon.

13. Summary • During the past several days, above-average rainfall was observed over western India, the Bay of Bengal, the South China Sea, Taiwan, Korea, the Philippine Sea, and the tropical central-eastern Indian Ocean. On the other hand, below-average rainfall was found over eastern India, Bangladesh, southern China, Japan, and the tropical western Pacific Ocean. • The NCEP Global Forecast System predicts that the monsoon circulation will be stronger than normal over South Asia, contributing to above normal Webster-Yang monsoon index, but weaker than normal over East Asia and the northwestern Pacific.

14. Onset of the Asian Monsoon

15. Climatology