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 August 23, 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, precipitation was above average (1979-95 climatology) over Kashmir region, northern Pakistan, Bangladesh, northeast India, much of Burma, the Arabian Sea, the Bay of Bengal, Bangladesh, equatorial Southeast Asia, eastern Indian Ocean, southeastern China, Japan, maritime Indonesia, and the northwestern Pacific storm track region. On the other hand, slightly below-average precipitation occurred over much of India, below normal rainfall over Indo-China peninsula, the Philippines, much of maritime Indonesia, and the subtropical western Indian Ocean and western Pacific (consistent with La Nina). It must be noted that there is a discrepancy between this data set and others such as the from the IMD. The discrepancy could also be because of the differing climatologies used as well. The % of normal 90-day accumulated precip map (right) shows the Middle East, northern Pakistan and Indian Kashmir region at over 200-250% of normal, as well as central northwestern Australia.

4. Precip Patterns: Last 30 Days During the past 30 days, precipitation was above average over much of tropical south Asia except peninsular, Gangetic Plains India (lack of monsoon depressions in northern Bay), eastern Indo-China peninsula, the Philippines and southeastern China. Above-average precipitation was also observed over northern India, northern Pakistan, the eastern Arabian Sea, southern and central Bay of Bengal, tropical central eastern Indian Ocean, and the northwestern Pacific storm track region. However, below-average also occurred over portions of India particularly eastern central India, equatorial western Pacific, Indochina peninsula, and northeastern Asia. Excessive precipitation was noted over northern India, Pakistan and near Gujarat, India.

5. Precip Patterns: Last 5 Days Rains were generally widespread across the entire summer monsoon region, however, for the five day period the precipitation was below normal over far eastern Asia and adjoining Pacific ocean particularly over Vietnam, Cambodia, Laos as well as over central east India and southeast China.

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: Southeast China rainfall excess continues. Middle panel:. Rainfall deficits in these regions continue. Lower panel : Coastal Western Ghats regions in peninsular India have received excessive rainfall so far this season.

7. Atmospheric Circulation The lack of monsoon depressions in the northern Bay of Bengal (combined with their usual northwesterly track) so far this season, is one of the primary reasons for the rainfall deficit In the north central and northeastern India. This week, a strange low level anomalous anticyclonic circulation is centered over the head Bay accentuating the lack of rainfall in the adjoining 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 rise up to normal level in the next couple of weeks after being below normal since early June. 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 July. 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 index will be near or slightly above 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 July. Green (brown) shading indicates increase (decrease) in rainfall associated with strong monsoon.

11. 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 East Asian WNP Monsoon Index will continue its up and down swing, as it has done in the past several weeks. 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 July. Green (brown) shading indicates increase (decrease) in rainfall associated with strong monsoon.

12. Summary • Except along the southeast-northwest oriented monsoon depressions track region in northern India, the rainfall is almost near normal over the Indian subcontinent. As the peak of the hurricane and typhoon season approaches in various storm oceans basins around the world approach, not a single monsoon depression has formed so far in the Bay of Bengal. The excessive rains that caused flooding in Kashmir and northern Pakistan have somewhat eased, but the lingering effects due to earlier heavy rains continue there.

13. Onset of the Asian Monsoon

14. Climatology