# Presentation: 546384

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

**Update prepared by**
**Climate Prediction Center / NCEP**
**   ****16 May 2008**

**For more information, visit:****  **_[http://www.cpc.ncep.noaa.gov/products/Global_Monsoons/Asian_Monsoons/Asian_Monsoons.shtml](http://www.cpc.ncep.noaa.gov/products/Global_Monsoons/Asian_Monsoons/Asian_Monsoons.shtml)_

## 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 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 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 Bay of Bengal, eastern Indian Ocean, the South China Sea, 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 much of the Southern Hemisphere including Madagascar, the Indian Ocean, and Australia. Precipitation was also below normal over the Middle East, eastern India, Bangladesh, the coastal regions of East and 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, western Indo-China peninsula, the South China Sea, and the subtropical northwestern Pacific (due to the effects of typhoon and tropical storms). Below-normal precipitation was observed over the tropical Indian Ocean, western-central Indonesia, southern and eastern China, and the east coast of Australia.**

## Recent Evolution: Rainfall

**Upper right: Before the impact of summer monsoon, the rainfall over southern China remained below normal.**
**Central-bottom right: The rainfall over the southern Indo-China peninsula, the Philippines, and other northern tropical lands in the AA monsoon region continued to be above normal.  **
**While the major rain band had shifted to the northern tropics, the precipitation over the southern tropics became mainly below normal.**

**For other boxes, see: http://www.cpc.ncep.noaa.gov/products/**
**Global_Monsoons/Asian_Monsoons/90d-precip_click_map.shtml**

## Convection has been further intensifying over the South China Sea and most of the (central-eastern) maritime continent.
Convection has becoming weaker over the eastern Bay of Bengal and western Indo-China peninsula and has been further suppressed over the tropical western-central Indian Ocean and Australia.
Convection has become weaker and been suppressed over East Asia including southern and eastern China.

**Convection has been further intensifying over the South China Sea and most of the (central-eastern) maritime continent.**
**Convection has becoming weaker over the eastern Bay of Bengal and western Indo-China peninsula and has been further suppressed over the tropical western-central Indian Ocean and Australia.**
**Convection has become weaker and been suppressed over East Asia including southern and eastern China.**

## Atmospheric Circulation: 200 mb

** ****Compared to the last week (left panel), the upper-level anomalous anti-cyclonic pattern over southern Asia and the easterly anomalies over its southern flank and over the Arabian Sea have become stronger, favoring an earlier establishment of large-scale Asian summer monsoon circulation.**

## Atmospheric Circulation: 850 mb

** ****Lower-level westerlies have extended eastward from the Bay of Bengal and the Indo-China peninsula to the South China Sea (SCS) and the Philippine Sea. **
** ****Westerlies have prevailed over the central SCS and anomalous westerly flow has clearly appeared and intensified over southern-central SCS (right panel), favoring an early onset of the SCS summer monsoon.**
** ****Northward cross-equatorial flow continues to be stronger than normal over the Indian Ocean.**

## 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 normal or stronger than normal, implying normal or above normal precipitation and lower-level westerly anomalies 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, 70-110E. 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/110-140E). The NCEP GFS predicts that, in the next two weeks, the monsoon circulation over East Asia and western North Pacific will be normal or stronger than normal, meaning normal or 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 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 appeared below normal. Below-normal precipitation was also observed over southern East Asia during the past several days. **
**Lower-level westerlies have prevailed over the Indo-China peninsula and southern-central South China Sea, favoring an early onset of the South China Sea summer monsoon.**
**The NCEP Global Forecast System predicts that the large-scale Asian monsoon circulation and the monsoon over East Asia and western North Pacific will be near normal or stronger than normal in the coming two weeks. It also predicts near-normal monsoon circulation over South Asia.**

## Onset Dates of ASM 

**Onset Dates of ASM**_ _

## Climatology