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 23 June 2008 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, heavy precipitation occurred over much of the maritime continent, tropical eastern Indian Ocean, tropical western and southwestern Pacific, and the North Pacific storm-track region. Precipitation was above normal over most of the tropical Northern Hemisphere except Papua New Guinea, and the equatorial Pacific east of 145E. Above-normal precipitation also appeared over Indian, southern China and southern Japan. Below-normal precipitation was found over the subtropical Southern Hemisphere including Madagascar, the Indian Ocean, and Australia. Precipitation was also below normal over the Middle East, east coast of Indo-China peninsula, and the subtropical North Pacific.

4. Rainfall Patterns: Last 30 Days Heavy precipitation occurred over the Northern Hemisphere tropical region and the North Pacific storm-track region. Precipitation was above normal over the Arabian Sea, Bay of Bengal, eastern maritime continent, tropical western Pacific, and the storm-track region. Above-normal precipitation also occurred over northeastern India, Nepal, southern China, South Korea, and southern Japan. Below-normal precipitation was found over much of the Southern Hemisphere especially over the tropical eastern Indian Ocean. Precipitation was also belownormal over Sri Lanka, Vietnam, and Papua New Guinea.

5. Rainfall Patterns: Last 5 Days Precipitation has increased significantly over northeastern India, southern China, South Korea, southern Japan, and the Philippine Sea during the last 5 days. Wet condition also appeared over the equatorial western Indian Ocean. Below-normal rainfall was observed over the eastern Arabian Sea, southern India, eastern Bay of Bengal, equatorial eastern Indian ocean, central South China Sea, and subtropical-extratropical northwestern Pacific Ocean.

6. Recent Evolution: Rainfall For other boxes, see: http://www.cpc.ncep.noaa.gov/products/ Global_Monsoons/Asian_Monsoons/90d-precip_click_map.shtml • Upper right: Associated with a northward shift of the front of East Asian monsoon rain-band, the rainfall over South Korea was above normal before a weakening in the recent days. • Central right: In spite of a recent pause, the rainfall over southern China was above normal associated with a northward shift of the Southeast Asian monsoon rain-band. • Bottom right: Over northern India, precipitation has remained clearly above normal.

7. Recent Evolution: OLR • The evolution of OLR indicates that the monsoon has intensified over southern China and weakened over northern India during the past week. • The dry areas over the eastern Indian Ocean and the wet areas over the western Indian ocean are corresponding to the tropical Indian Ocean dipole, which is in its developing stage.

8. Atmospheric Circulation • The cross-equatorial flow over the western Indian Ocean remained stronger than normal and the strong Somalia jet brought large amount of water vapor to northwestern India. • Enhanced lower-level jet was observed over the coast of China, South Korea, and southern Japan accompanied by strong Mei-yu (Baiu) front and heavy rainfall over the regions.

9. NCEP/GFS Model Forecasts Bias-Corrected Precipitation for Week 1 & Week 2

10. W-Y Monsoon Prediction • Upper panel: Webster-Yang monsoon index (Webster and Yang 1992) defined as the mean U850-U200 over 0-20N, 40-110E. The NCEP GFS predicts that, in the next two weeks, the large-scale Asian monsoon circulation will be weaker than normal. • Lower panel: Correlation between precipitation and the Webster-Yang monsoon index (Webster and Yang 1992; shading) and regression of 850-mb winds against the monsoon index (vectors) for June.

11. SA Monsoon Prediction • Upper panel: South Asian monsoon index (Goswami et al. 1999) defined as the mean V850-V200 over 10-30N, 70-110E. The NCEP GFS predicts that the South Asian monsoon circulation will near or above normal in the next two weeks. • Lower panel: Correlation between precipitation and the South Asian monsoon index (Goswami et al. 1999; shading) and regression of 850-mb winds against the monsoon index (vectors) for June.

12. EA-WNP Monsoon Prediction • Upper panel: East Asian – Western North Pacific monsoon index (Wang et al. 2008) defined as the mean difference of U850(5-15N/90-130E) – U850(20-30N/110-140E). The NCEP GFS predicts that, in the next two weeks, the monsoon circulation over East Asia and the western North Pacific will be mainly weaker than normal. • Lower panel: Correlation between precipitation and the East Asian – Western North Pacific monsoon index (Wang et al. 2008; shading) and regression of 850-mb winds against the monsoon index (vectors) for June.

13. Summary • Above-normal precipitation occurred over most of the tropical Asian-Australian region during the past three months. Above-normal precipitation was also found over the Arabian Sea, Bay of Bengal, most of India, southern China, East Asia, and most of the maritime continent and western North Pacific in last month. • Below-normal precipitation appeared over most of the tropical-subtropical Southern Hemisphere. The Middle East was also drier than normal during the past three months. Dry conditions were clearly seen over the tropical central-eastern Indian Ocean and central China Sea in the past month. • While the major rain belt had further shifted to the northern tropics, the precipitation over the South China Sea continued to be below normal. • The rainfall over northern India, southern China, South Korea, and southern Japan was above normal during the last week. • The NCEP GFS predicts that overall the Asian monsoon is shifting to a weak phase.

14. Onset Dates of ASM

15. Climatology