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 30 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 India, 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 the Indo-China peninsula, and western tropical 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 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 and southern China 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, part of tropical central-eastern Indian Ocean, Southeast Asia, the South China Sea, and central China.

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 Japan was above normal before a weakening in the recent days. • Central right: After a northward shift of the Southeast Asian monsoon, the precipitation over southeastern China was near normal. • Bottom right: Over northern India, precipitation has remained above normal.

7. Recent Evolution: OLR • The evolution of OLR indicates that the monsoon has weakened over southern China and 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 and the Somalia jet were near normal last week. • Lower-level jet shifted to the south of Japan, accompanied by a strong Baiu front and heavy rainfall over Japan.

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 July.

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 tends to be moderately stronger than 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 July.

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 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 July.

13. Summary • Above-normal precipitation occurred over most of the Northern Hemisphere tropical 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, 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. Precipitation was also belownormal over Sri Lanka, Vietnam, and Papua New Guinea last month. • Rainfall was above normal over northeastern India and southern China but below normal over central China during the last week. • The NCEP GFS predicts that overall the large-scale Asian monsoon will be weaker than normal.

14. Onset Dates of ASM

15. Climatology