The Asian-Australian Monsoon System: Recent Evolution, Current Status and Prediction Update prepared by Climate Prediction Center / NCEP 9 May 2008 For more information, visit:

Outline Recent Evolution and Current Conditions Monsoon Prediction Summary Climatology

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, western-central Indonesia, 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 Australia. Precipitation was also below normal over the Middle East, western Asia, the coastal regions of East and Northeast Asia, and the subtropical North Pacific.

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

Rainfall Patterns: Last 5 Days The precipitation pattern during the last 5 days was characterized by the heavy and above-normal precipitation over the eastern Bay of Bengal and west coast of Indo-China peninsula (due to the effect of cyclone Nargis), eastern Indonesia, and the subtropical northwestern Pacific storm-track region. The precipitation over the tropical Indian Ocean (especially over the east), western Indonesia, east coast of Australia, and equatorial western Pacific was below normal.

Recent Evolution: Rainfall Upper-right: Myanmar had been dried for months but cyclone Nargis caused the 90-day accumulated precipitation well above normal. Central-right: As in many locations over the maritime continent, the precipitation over the Philippines has been continuously above normal. Bottom-right: The recent increase in precipitation over southern Indo-China peninsula may be an important feature associated with monsoon activity. Climatologically, the onset of the local monsoon occurs during May. For other boxes, see: Global_Monsoons/Asian_Monsoons/90d-precip_click_map.shtml

Recent Evolution: OLR After the landing of cyclone Nargis in Myanmar, convection has weakened over the Bay of Bengal but been further suppressed over the equatorial eastern Indian Ocean (central and bottom panels). Convection tends toward normal over subtropical Asia and to become stronger over eastern maritime continent and weaker over Australia.

Atmospheric Circulation: 200 mb The upper-tropospheric westerlies have become weaker (stronger) significantly over the subtropics of the Northern (Southern) Hemisphere, implying a large change from the winter regime to the summer circulation regime. Compared to the last week (left panel), the tropical upper-tropospheric easterlies and the cross-equatorial flow have become stronger. During the past week, the tropical easterly flow was clearly stronger than normal (right panel).

Atmospheric Circulation: 850 mb The lower-tropospheric westerlies intensified over the Bay of Bengal and began to appear over the Indo-China peninsula and southern South China Sea (SCS). Easterly flow became weaker over the central SCS and near the Philippines. These conditions favor an onset of monsoon over SCS. The westerly anomalies over the southern-central SCS and its east (right panel) favor an early onset of the SCS summer monsoon. Northward cross-equatorial flow began to appear over the western Indian Ocean and it was stronger than normal.

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 GFS predicts that, in the next two weeks, the large-scale monsoon circulation will remain stronger than normal, implying above normal precipitation and westerly anomalies at the lower troposphere over tropical Asia including the Indo-China peninsula and the South China Sea. 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.

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 GFS predicts that the South Asian monsoon circulation will be close to 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.

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 GFS predicts that, in the next two weeks, the monsoon circulation over East Asia and western North Pacific will remain stronger than normal, meaning above normal precipitation over the northern maritime continent and tropical 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.

Summary Above-normal precipitation occurred over the tropical Asian- Australian sector 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. Lower-tropospheric westerlies began to appear over the Indo- China peninsula and southern South China Sea, favoring an early onset of the South China Sea monsoon. 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.

Onset Dates of ASM

Climatology