Madden/Julian Oscillation: Recent Evolution, Current Status and Forecasts

1. Madden/Julian Oscillation: Recent Evolution, Current Status and Forecasts Update prepared by Climate Prediction Center / NCEP June 27, 2005

2. Outline • Overview • Recent Evolution and Current Conditions • Madden Julian Oscillation Forecast • Summary

3. Overview • The Kelvin wave initiated by westerlies near the date line in late January 2005 has reached the South American coast and warming of the ocean waters along the west coast of South America has ended. • During mid March the MJO became active and strong and completed one cycle around the global tropics with a period of approximately 45 days. Westerly anomalies in the western Pacific during mid-April associated with this MJO activity did not extend far enough east to initiate another Kelvin wave. • The MJO has been weak since the middle of May. Over the last week convection has been persistent over the eastern Indian Ocean, Bay of Bengal and South China Sea regions. The westerly anomalies in the eastern Indian Ocean continue to extend eastward toward Indonesia, while the easterly anomalies in the western Pacific have been persistent for the last several weeks. Forecasts of the MJO continue to indicate weak MJO activity over the next 1-2 week period. • An increased chance of above normal rainfall exists for Southeast Asia, the Bay of Bengal region and sections of India for weeks 1 and 2. For Central America there exists a increased chance of above normal rainfall for week 1. Tropical cyclone activity in the eastern Pacific basin is expected to be at or above normal. If the area of convection and upper-level divergence, located over the eastern Indian Ocean/western Indonesian region, continues to extend eastward there is an increased risk of above normal rainfall for the tropical western Pacific to the east of the Philippines.

4. 850-hPa Vector Wind Anomalies (m s-1) Note that shading denotes the magnitude of the anomalous wind vectors. Easterly anomalies have been persistent over the tropical western Pacific. Westerly anomalies have returned to the eastern Pacific. Westerly anomalies continue to extend eastward toward the western Pacific.

5. Low-level (850-hPa) Zonal (east-west) Wind Anomalies (m s-1) Weaker-than-average easterlies (orange/red shading). Stronger-than-average easterlies (blue shading). Westerly anomalies developed over the western equatorial Pacific in early January and persisted through February. After a sustained period of easterly anomalies, westerly anomalies returned to the tropical western Pacific in April. Time The latest period of sustained westerly anomalies occurred in late May. Currently broad scale easterly anomalies are observed west of the date line over the tropical Pacific. Westerly anomalies have continued to extend eastward over the Indian Ocean towards the western Pacific. Longitude

6. Outgoing Longwave Radiation (OLR) Anomalies (7.5°S-7.5°N) Drier-than-average conditions (orange/red shading) Wetter-than-average conditions (blue shading) The eastward propagation of the positive/negative anomaly dipole over the Indian Ocean and Indonesia (late December 2004-early January 2005) was associated with the MJO. Time Enhanced convection became persistent in the region of the anomalously warm water near the date line during February. The MJO was strong from late March through mid May, but has weakened over the last month. Currently convection is located over eastern Indian Ocean and western Indonesia. Longitude

7. Outgoing Longwave Radiation (OLR) Anomalies (2.5°N-17.5°N) Drier-than-average conditions (orange/red shading) Wetter-than-average conditions (blue shading) Time Over the last 3 weeks convection has been concentrated over the Indian Ocean. Longitude

8. Anomalous OLR and 850-hPa Wind: last 30 days The northward displacement of convection is evident over the Southeast Asian region in the middle part of the period. The ITCZ over the eastern Pacific has been weak over the period. Over the last 10 days convection has been concentrated over the eastern Indian Ocean. Over the last 20 days easterly anomalies have been persistent over the tropical western Pacific. The anomalous westerlies in the tropical eastern Pacific developed in the middle part of the period.

9. 200-hPa Velocity Potential Anomalies (5°S-5°N) Positive anomalies (orange/red shading) indicate unfavorable conditions for precipitation. Negative anomalies (blue shading) indicate favorable conditions for precipitation. A stationary pattern of upper level divergence developed during February as enhanced convection remained near the date line. Beginning in early-mid March, the MJO became quite active and regular. Upper-level divergence propagated from the western Indian Ocean across the Pacific and through the western Hemisphere during a 45 day period from mid March to early May. The MJO has been weak over the last month. Currently broad-scale upper-level convergence is found over the tropical Pacific with an area of upper-level divergence centered near 100oE. Time Longitude

10. 200-hPa Vector Winds and Anomalies (m s-1) Note that shading denotes the magnitude of the anomalous wind vectors.

11. Heat Content Evolutionin the Eq. Pacific • Through 2004 and 2005 there were several cases of eastward-propagating oceanic Kelvin waves (indicated by dashed black lines in the figure). • Each Kelvin wave was initiated when the easterlies weakened over the equatorial Pacific in association with Madden-Julian Oscillation (MJO) activity. • Between August 2004 and January 2005 Kelvin wave activity weakened and the average heat content (0-300 m) decreased. • During February 2005, a stronger Kelvin wave developed and continued to strengthen during March and reached the South American coast during early April. Heat content has returned to near average in the western and central Pacific with no new Kelvin wave activity. Time Longitude

12. Empirical Forecast Based on the Real-time Multivariate MJO index Weak MJO activity is forecasted for the next 6-10 day period.

13. Potential Global Hazards –Week 1 3 2 1 Increased chance of above average rainfall. Tropical storm Calvin will impact the eastern Pacific west of Central America. Increased chance of above average rainfall.

14. Potential Global Hazards – Week 2 1 Increased chance of above average rainfall.

15. Summary • The Kelvin wave initiated by westerlies near the date line in late January 2005 has reached the South American coast and warming of the ocean waters along the west coast of South America has ended. • During mid March the MJO became active and strong and completed one cycle around the global tropics with a period of approximately 45 days. Westerly anomalies in the western Pacific during mid-April associated with this MJO activity did not extend far enough east to initiate another Kelvin wave. • The MJO has been weak since the middle of May. Over the last week convection has been persistent over the eastern Indian Ocean, Bay of Bengal and South China Sea regions. The westerly anomalies in the eastern Indian Ocean continue to extend eastward toward Indonesia, while the easterly anomalies in the western Pacific have been persistent for the last several weeks. Forecasts of the MJO continue to indicate weak MJO activity over the next 1-2 week period. • An increased chance of above normal rainfall exists for Southeast Asia, the Bay of Bengal region and sections of India for weeks 1 and 2. For Central America there exists a increased chance of above normal rainfall for week 1. Tropical cyclone activity in the eastern Pacific basin is expected to be at or above normal. If the area of convection and upper-level divergence, located over the eastern Indian Ocean/western Indonesian region, continues to extend eastward there is an increased risk of above normal rainfall for the tropical western Pacific to the east of the Philippines.