The Asian-Australian Monsoon System: Recent Evolution and Current Status

1. The Asian-Australian Monsoon System: Recent Evolution and Current Status Update prepared by Climate Prediction Center / NCEP 2 May 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 and southern Indian Ocean, tropical western 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 150E. 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 central Australia. Precipitation was also below normal over the Middle East, western Asia, the coastal regions of East and Northeastern Asia, and the subtropical North Pacific.

4. Rainfall Patterns: Last 30 Days During the past 30 days, heavy precipitation occurred over the tropics (except the western Indian Ocean) and the North Pacific storm-track region. Precipitation was above normal over the tropical Bay of Bengal, the maritime continent (except Papua New Guinea), tropical western Pacific (except the equatorial Pacific east of 150E), and 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, Myanmar, part of Indonesia, the coastal regions of southern China and eastern Indo-China peninsula, Northeast Asia, and subtropical northwestern Pacific.

5. Rainfall Patterns: Last 5 Days The precipitation pattern during the last 5 days was characterized by the above-normal precipitation over the Bay of Bengal and the below-normal precipitation over the tropical-subtropical Southern Hemisphere (especially over the Indian Ocean), east coast of Australia, southeastern China, Japan, and Korea.

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 precipitation over the Indo-China peninsula has been above normal for weeks. Whether the onset of the local monsoon is earlier than normal deserves particular attentions. • Central-right: The precipitation over southern India has been near normal during the past weeks despite that the heavy precipitation in March significantly increased the accumulated precipitation. • Bottom-right: Over Top End Australia, the precipitation has been below normal for weeks although the accumulated precipitation for the season was above normal. • The accumulated precipitation over other tropical boxes has been mostly above normal during this season.

7. Recent Evolution: OLR • The convection over the Bay of Bengal has intensified and the convection over the equatorial eastern Indian Ocean has been suppressed after a northward shift of the convective center (central and bottom panels). • Except the dryness over western Indonesia and the wetness over the Philippines, convection remains mainly normal over the maritime continent and adjacent regions (bottom panel).

8. Atmospheric Circulation & OLR Last Week • Upper-right: An upper-tropospheric anticyclonic pattern controlled southern Asia and the cross-equatorial flow over eastern Indian Ocean was stronger than normal. • Lower-right: Note the cyclonic pattern over the Bay of Bengal, which was energized by the strong cross-equatorial flow and the northeasterly flow over the South China Sea and the Indo-China peninsula. The trade winds over the tropical central-western Indian Ocean and western Pacific were stronger than normal.

9. WY 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 stronger than normal, implying above normal precipitation and westerly anomalies at the lower troposphere over tropical Asia. • 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 May.

10. 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 mainly near 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 May.

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/110-140E). The NCEP GFS predicts that, in the next two weeks, the monsoon circulation over East Asia and western North Pacific will be stronger than normal, meaning above normal precipitation over the northern maritime continent and the northwestern Pacific. • 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 May.

12. Summary • Above-normal precipitation occurred over the tropical Asian-Australian sector from 15S to 10N during the past months, except over the equatorial western Pacific (east of 150E) 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, central Australia, and the subtropical northwestern Pacific high region. The Middle East and western Asia were also drier than normal during the past months. • The NCEP GFS predicts that the large-scale Asian monsoon circulation and the monsoon over East Asia and northwestern Pacific will be stronger than normal in the coming two weeks. It also predicts near-normal monsoon circulation over South Asia.

13. Onset Dates of ASM

14. Climatology