1. Climate Prediction Center / NCEP
The Asian-Australian Monsoon System: Recent Evolution, Current Status and Prediction
Update prepared by
Climate Prediction Center / NCEP
4 August 2008
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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 equatorial and northern tropical Indian Ocean, the Bay of Bengal, northern India, southern China, Philippines, the Philippine Sea, and the northwestern Pacific. Precipitation was below normal over southern India, Myanmar, the eastern Indo-China peninsula, western-central Indonesia, Papua New Guinea, Australia, and the tropical Southern Hemisphere especially the eastern Indian Ocean.

4. Rainfall Patterns: Last 30 Days
During the past 30 days, above normal precipitation occurred over the equatorial central-eastern Indian Ocean, northern India, the Bay of Bengal, southern China, the South China Sea, eastern Indonesia, and subtropical North Pacific. However, precipitation was below normal over southern India, eastern Indo-China peninsula, southern Japan and vicinity, and the tropical southeastern Indian Ocean.

5. Rainfall Patterns: Last 5 Days
Above-normal precipitation appeared over the tropical central Indian Ocean, northeastern India, southern Bay of Bengal, southern South China Sea, subtropical northwestern Pacific, and from central China to Korea during the last 5 days. Below-normal precipitation was observed over eastern India, Bangladesh, Myanmar, Indo-China peninsula, northern South China Sea, southern Japan, Philippines, the Philippine Sea, and tropical southeastern tropical Indian Ocean.

6. Recent Evolution: Rainfall
For other boxes, see:
Global_Monsoons/Asian_Monsoons/90d-precip_click_map.shtml
Upper right: The rainfall over northern China has been continuously below normal
Central right: But precipitation over southern China has been above normal for the season.
Bottom right: Even though west coast of peninsular India got above normal rainfall recently, for the season as a whole the cumulative rainfall over southern India is still below normal. Also, in spite of the weaker rains in the past week or so, northern India (time series not shown) has received above normal rainfall for the season as a whole so far.

7. Atmospheric Circulation
The weak cyclonic circulation over northeastern China brought moisture from the adjacent oceans to eastern China.
Anomalous southeasterly moisture flow from the northern Bay of Bengal continues to bring above normal rains to Northern India. The stronger than normal Somali Jet also brought excess rainfall for the week to the southwestern coast of India.

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

9. W-Y Monsoon Prediction
Upper panel: Webster-Yang monsoon index (Webster and Yang 1992) defined as the mean U850-U200 over 0-20N, E. The NCEP Global Forecast System predicts that, in the next two weeks, the large-scale Asian monsoon circulation will hover around normal conditions.
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 August.

10. SA Monsoon Prediction
Upper panel: South Asian monsoon index (Goswami et al. 1999) defined as the mean V850-V200 over 10-30N, E. The NCEP Global Forecast System predicts that the South Asian monsoon circulation will become slightly 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 August.

11. 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/ E). The NCEP Global Forecast System predicts that, in the next two weeks, the monsoon circulation over East Asia and the western North Pacific will change dramatically from above normal to below normal conditions.
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 August.

12. Summary
So far precipitation, for the 2009 summer monsoon season as a whole, exhibited markedly different characteristics over India and China. Over China, precipitation was below normal over northeastern China while it was above normal over southern China. But over India, northern India the accumulated monsoon rainfall so far this season was above normal while it was below normal in the south. There is a considerable deficit of monsoon precipitation so far over Bangladesh, Myanmar, and eastern Indo-China peninsula.
The NCEP GFS predicts that the large-scale Asian monsoon will hover around normal conditions for the next two weeks.

13. Onset Dates of ASM

14. Climatology