Recent Evolution and Current Status of the Asian-Australian Monsoon System

1. The Asian-Australian Monsoon System: Recent Evolution, Current Status and Prediction Update prepared by Climate Prediction Center / NCEP 18 May 2009 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. Rainfall Patterns: Last 90 Days During the past 90 days, above-normal precipitation occurred over the tropics east of 95E (except Indonesia), the Coral Sea, and extratropical northwestern Pacific. Below-normal precipitation was observed over the Middle East, northern India, southern China, Korea, and southern Japan. Precipitation over tropical Indian Ocean, Australia, Madagascar, and southern-subtropical Indian Ocean was also below normal.

4. Rainfall Patterns: Last 30 Days During the past 30 days, above-normal precipitation occurred mainly over the South China Sea, the Philippines, the Philippine Sea, the Indo-China peninsula, south of Java, and the Arafura Sea. Below-normal precipitation was clearly observed over eastern Africa, the Indian Ocean, eastern India, East Asia, Indonesia, and Australia.

5. Rainfall Patterns: Last 5 Days Above-average rainfall was observed over the equatorial central-eastern Indian Ocean and south of Java last week. In the meantime, below-normal rainfall occurred over East Asia, the East China Sea, and the off-equator regions of the tropical Indian 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: Dry conditions appear over southern China persistently. • Middle panel: The rainfall over the Philippines has been mostly above average during past several months. • Bottom panel: While rainfall has been mostly over normal over southern Indo-China peninsula, the recent heavy rainfall has relieved the dry conditions over the central-northern part of the peninsula.

7. Atmospheric Circulation When the trade wind over tropical southern Indian Ocean and the westerly monsoon flow over western Arabian Sea have strengthened, easterly flow has re-controlled the South China Sea, adding difficulties to predict the onset of the local monsoon. The anomalous cyclonic pattern over southern-tropical eastern Indian Ocean should also be noticed.

8. NCEP/GFS Model Forecasts Bias-Corrected Precip. Anom. for Week 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). The NCEP Global Forecast System predicts that the large-scale monsoon circulation will be slightly weaker than normal in the next two weeks. Lower panel: Correlation between precipitation and Webster-Yang monsoon index (Webster and Yang 1992; shading) and regression of 850-mb winds on the monsoon index (vectors) for May.

10. 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). The NCEP Global Forecast System predicts that, in the next two weeks, the EAWNP monsoon circulation is changing from a weak stage to normal or above normal condition. Lower panel: Correlation between precipitation 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 May.

11. Summary • Above-average rainfall was observed over the equatorial central-eastern Indian Ocean and south of Java last week. In the meantime, above-normal rainfall occurred over East Asia, the East China Sea, and the off-equator regions of the tropical Indian Ocean. • The NCEP GFS predicts weak or normal monsoon condition over Southeast Asia in the next two weeks.

12. Onset of the Asian Monsoon

13. Climatology