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 2 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 equatorial Indian Ocean, southern Arabian Sea, and East Asia including southern China during the last 5 days. Super Typhoon Nakri has caused very heavy precipitation over the Philippine Sea. Most of the southern tropics and subtropics are 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 has become below normal after the monsoon rain-band shifted northward. • Bottom right: Onset of summer monsoon has occurred over southern India and the rainfall associated with the local monsoon onset was slightly above normal.

7. Recent Evolution: OLR • As the monsoon rain-band shifted further northward, convection has increased over 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 tropical Indian Ocean, especially the western and equatorial portions, has become more convective.

8. Atmospheric Circulation • Right: An anomalous cyclonic pattern was over the eastern Arabian Sea and several anti-cyclonic patterns were over the Bay of Bengal and its east. These features, together with the above-normal cross-equatorial flow over the western Pacific, favor a strong monsoon over South Asia and weak monsoon conditions over Southeast Asia. • An anomalous upper-level cyclonic pattern and a low-level anti-cyclonic pattern controlled Australia, which are unfavorable for convection to develop.

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 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 be becoming 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 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. • 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. • While major rain belt had shifted to the northern tropics, the precipitation over the southern tropics and Southeast Asia appeared below normal. • Onset of summer monsoon has started over southern India. • The NCEP Global Forecast System predicts that the monsoons tend to strengthen over South Asia but weaken over Southeast Asia in the coming two weeks.

14. Onset Dates of ASM

15. Climatology