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 9 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 tropics except the western Indian Ocean, Papua New Guinea, and the equatorial Pacific east of 145E. Above-normal precipitation also appeared over the storm-track region. 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, western Asia, the coastal regions of East Asia, and the subtropical North Pacific high area.

4. Rainfall Patterns: Last 30 Days Heavy precipitation occurred over the tropics and the North Pacific storm-track region. Precipitation was above normal over southern Arabian Sea, the Bay of Bengal, the South China Sea, eastern maritime continent, tropical western Pacific, and the storm-track region. Above-normal precipitation was also seen over southwestern China. Below-normal precipitation was found over much of the Southern Hemisphere including Madagascar, the Indian Ocean, and Australia. Precipitation was also below normal over western Indonesia, Papua New Guinea, and the equatorial western Pacific east of 150E.

5. Rainfall Patterns: Last 5 Days Precipitation has increased over the central equatorial Indian Ocean, southern Arabian Sea, and southern China coast during the last 5 days. Below-normal rainfall was observed over the Bay of Bengal, central South China Sea, and central-eastern China. Most of the southern tropics and subtropics are still characterized by normal or slightly below normal precipitation.

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: The rainfall over southern China (also southwestern China including Sichuan; figure not shown) has increased and has been above normal associated with a northward shift of the Southeast Asian monsoon rain-band. • Central right: The rainfall over the Indo-China peninsula and central South China Sea continued to be below normal after the monsoon rain-band shifted northward. • Bottom right: After the onset local monsoon, the rainfall over southern India was mainly near normal.

7. Recent Evolution: OLR • As the monsoon rain-band shifted further northward, convection has increased over the coast of East Asia but decreased over the South China Sea. The anomalies of convection are weakening over the southern tropics and subtropics. • The atmosphere over the equatorial tropical Indian Ocean and Indonesia region has become more convective.

8. Atmospheric Circulation • The cross-equatorial flow intensified over western Indian Ocean and more water vapor was transported to eastern Arabian Sea and western India. • Anomalous lower-level anti-cyclonic patterns were observed over the central-northern South China Sea and the northwestern Pacific. • An anomalous upper-level cyclonic pattern controlled Australia.

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 monsoon circulation will be near normal or slightly stronger 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 remain 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 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 months except over the equatorial western Pacific (east of 145E) and the tropical western Indian Ocean. Above-normal precipitation was also found over the subtropical western Pacific storm-track region last months and over the Arabian Sea last month. • Below-normal precipitation appeared over the subtropical southern Indian Ocean, Madagascar, Australia, and the subtropical northwestern Pacific high region. The Middle East and western Asia were also drier than normal during the past months, and dry condition was seen over western Bay of Bengal, Sri Lanka, and western Indonesia last month as well. • While major rain belt had shifted to the northern tropics, the precipitation over the southern tropics and the South China Sea appeared below normal. Monsoon rainfall was above normal over southern China. • After the onset of local monsoon, the rainfall over southern India was near normal. • The NCEP Global Forecast System predicts that the monsoon circulation tends to strengthen over South Asia but weaken over Southeast Asia in the coming two weeks.

14. Onset Dates of ASM

15. Climatology