1. Madden/Julian Oscillation: Recent Evolution, Current Status and Forecasts Update prepared by Climate Prediction Center / NCEP April 26, 2005

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

3. Overview MJO activity during June-October and December 2004-January 2005 resulted in significant variability in the atmosphere (wind, pressure) and Pacific Ocean (surface and subsurface temperature). This activity was associated with periods of significant weakening of the low-level easterly winds over the equatorial Pacific and was related to the initiation of eastward-propagating oceanic Kelvin waves. 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 is ongoing. Above average SST’s can be expected in these areas over the next 1-2 weeks. The well-established moderate to strong MJO continues. Based on the latest evolution of the MJO and statistical model forecasts, it is likely that suppressed convection will prevail across Indonesia and the western Pacific while enhanced convection affects equatorial South America and the Gulf of Guinea/southern Sahel and eastern parts of Africa. Impacts in the global tropics include drier than normal conditions for Indonesia and the western Pacific during the next week and above average rainfall across equatorial regions of South America (week 1) and the following areas of Africa: Gulf of Guinea/southern Sahel, southeast Sudan, Ethiopia, and Somalia (weeks 1-2).

4. 850-hPa Vector Wind Anomalies (m s -1 ) Note that shading denotes the magnitude of the anomalous wind vectors. The equatorial westerly anomalies have weakened during the last five days.

5. Low-level (850-hPa) Zonal (east- west) Wind Anomalies (m s -1 ) Longitude Time Weaker-than-average easterlies (orange/red shading). Stronger-than-average easterlies (blue shading). The westerly anomalies in the western Pacific have weakened during the last week. Stronger than average easterlies are centered over and to the east of the date line in the equatorial Pacific. Westerly anomalies developed over the western equatorial Pacific in early January and persisted through February.

6. Enhanced convection became persistent in the region of the anomalously warm water near the date line during February. Outgoing Longwave Radiation (OLR) Anomalies (7.5°S-7.5°N ) Drier-than-average conditions (orange/red shading) Wetter-than-average conditions (blue shading) Longitude Time 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. Enhanced convection has propagated eastward from Indonesia towards the date line. Suppressed convection now stretches from the Indian Ocean and into Indonesia.

7. Anomalous OLR and 850-hPa Wind: last 30 days During the last 30 days negative OLR anomalies (above-average rainfall) shifted eastward from the Indian Ocean, to Indonesia and then into the western Pacific. Low-level (850- hPa) easterly wind anomalies (m/s) observed over the central equatorial Pacific, weakened and westerly anomalies developed over the western equatorial Pacific. W m -2

8. 200-hPa Velocity Potential Anomalies Negative anomalies (blue shading) indicate favorable conditions for precipitation. Positive anomalies (orange/red shading) indicate unfavorable conditions for precipitation. Longitude The eastward propagation of negative anomalies over the Indian ocean and positive anomalies over Indonesia and the Pacific during December/early January was associated with the MJO. A more stationary pattern developed during February. Upper-level divergence has propagated across the date Line into the eastern Pacific. Upper-level convergence (suppressed phase of the MJO) has strengthened and propagated across Indonesia. Time

9. 200-hPa Vector Winds and Anomalies (m s -1 ) Note that shading denotes the magnitude of the anomalous wind vectors. Upper-level westerlies continue to strengthen in the Indian Ocean.

10. Heat Content Evolution in the Eq. Pacific Through 2004 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. The amplitude of the Kelvin wave is comparable to the Kelvin wave which developed during June-July 2004. Longitude Time

11. The convection associated with the MJO is forecast to weaken across the central equatorial Pacific. The area of suppressed convection, currently located over the Indian Ocean and Indonesia, is forecast to propagate eastward across the western Pacific. Empirical Forecast Based on the Real-time Multivariate MJO index

12. Potential Global Impacts (1) Drier-than-normal conditions expected for Indonesia and the western Pacific (week 1) (2) Increased likelihood of above average rainfall over equatorial South America (week 1) (3) Enhanced likelihood of above average rainfall in the Gulf of Guinea and southern Sahel regions of Africa (weeks 1-2) (4) Above average rainfall will benefit agriculture in southeast Sudan, Ethiopia, and Somalia while enhanced convection is anticipated for the western Indian Ocean (week 1-2) 1 2 3 4

13. Summary MJO activity during June-October and December 2004-January 2005 resulted in significant variability in the atmosphere (wind, pressure) and Pacific Ocean (surface and subsurface temperature). This activity was associated with periods of significant weakening of the low-level easterly winds over the equatorial Pacific and was related to the initiation of eastward-propagating oceanic Kelvin waves. 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 is ongoing. Above average SST’s can be expected in these areas over the next 1-2 weeks. The well-established moderate to strong MJO continues. Based on the latest evolution of the MJO and statistical model forecasts, it is likely that suppressed convection will prevail across Indonesia and the western Pacific while enhanced convection affects equatorial South America and the Gulf of Guinea/southern Sahel and eastern parts of Africa. Impacts in the global tropics include drier than normal conditions for Indonesia and the western Pacific during the next week and above average rainfall across equatorial regions of South America (week 1) and the following areas of Africa: Gulf of Guinea/southern Sahel, southeast Sudan, Ethiopia, and Somalia (weeks 1-2).