1. Madden/Julian Oscillation: Recent Evolution, Current Status and Forecasts Update prepared by Climate Prediction Center / NCEP August 22, 2005

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

3. Overview During mid-March the MJO became active and completed two cycles around the global tropics that lasted until mid-May. An eastward propagating oceanic Kelvin wave initiated by persistent westerly anomalies near the date line in February reached the South American coast in April. There has been no additional oceanic Kelvin wave activity. The MJO remains weak. Convective anomalies across most of the equatorial global tropics are very weak. Low-level easterly anomalies are mainly north of the equator across northern Indonesia and the western Pacific Ocean. The MJO is expected to remain weak for the next 1-2 weeks. Potential benefits/hazards in the global tropics, however, still include an enhanced chance of tropical cyclone development for weeks 1 and 2 in the Atlantic Basin and for week 1 in the eastern Pacific Basin. Currently, Typhoon Mawar and Tropical storm Guchol will impact areas in the northwest Pacific including Japan while Hurricane Hillary will affect the eastern Pacific Ocean. Meanwhile, above average rainfall is possible across areas of Central America, southern Mexico, and Florida as well as sections of the Caribbean Sea and the Gulf of Mexico during week 1. In addition, there is an increased chance of above average rainfall across west- central Africa during both weeks 1 and 2.

4. 850-hPa Vector Wind Anomalies (m s -1 ) Note that shading denotes the magnitude of the anomalous wind vectors. Easterly anomalies north of the equator have shifted west and strengthened. Widespread westerly anomalies continue in the eastern Pacific.

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). During June through early July, easterly anomalies dominated the western equatorial Pacific Eastward propagating anomalies existed from mid- March until mid-May. In early August, a period of westerly anomalies were evident in the western Pacific. Most recently, equatorial easterly anomalies have weakened.

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) Longitude Time The MJO was strong from late March through mid-May but has been very weak during June, July and August. Current anomalies of either sign are weak across most of the equatorial global tropics.

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) Longitude Time A period of enhanced convection north of the equator in the far western Pacific was evident during late July and early August. During the last week, suppressed convection north of the equator stretches from Indonesia into the western Pacific. Recently, enhanced convection has developed across Central America.

8. Anomalous OLR and 850-hPa Wind: Last 30 days Suppressed convection developed across Indonesia during early August. Easterly anomalies in the western Pacific north of the equator have shifted west during August. 30 JUL 2005

9. 200-hPa Velocity Potential Anomalies (5°S-5°N ) Negative anomalies (blue shading) indicate favorable conditions for precipitation. Positive anomalies (orange/red shading) indicate unfavorable conditions for precipitation. Longitude Eastward propagating upper- level convergence and divergence is evident from March through Mid-May indicative of the strong MJO during this period. The MJO has been weak since June. Regions of upper level divergence and convergence have generally been stationary with a eastward shift in late July and early August. Time

10. 200-hPa Vector Winds and Anomalies (m s -1 ) Note that shading denotes the magnitude of the anomalous wind vectors. Cross equatorial southerly anomalies over Indonesia have developed during the past ten days.

11. 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. During February 2005, a strong Kelvin wave (initiated by persistent westerly anomalies near the date line unrelated to the MJO) developed and continued to strengthen during March and reached the South American coast during early April. Heat content has returned to near average across much of the Pacific although above average values are evident in the western Pacific during June and July. Heat Content Evolution in the Eq. Pacific Longitude Time

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

13. Potential Benefits/Hazards –Week 1 (1)Typhoon Mawar and Tropical Storm Guchol are expected to impact the northwest Pacific Ocean and Japan (2)Increased chance of above average rainfall across Central America, southern Mexico, and Florida as well as areas in the Caribbean Sea, Gulf of Mexico, and Florida. (3)Hurricane Hillary is expected to affect the eastern Pacific Ocean. Also, there is an increased chance of tropical cyclogenesis in the eastern Pacific. (4)Increased chance of tropical cyclogenesis across sections of the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico. (5)Increased chance of above average rainfall across west-central Africa. 3 2 54 1

14. Potential Benefits/Hazards – Week 2 (1)Increased chance of tropical cyclogenesis across sections of the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico. (2)Increased chance of above average rainfall across west-central Africa. 1 2

15. Summary During mid-March the MJO became active and completed two cycles around the global tropics that lasted until mid-May. An eastward propagating oceanic Kelvin wave initiated by persistent westerly anomalies near the date line in February reached the South American coast in April. There has been no additional oceanic Kelvin wave activity. The MJO remains weak. Convective anomalies across most of the equatorial global tropics are very weak. Low-level easterly anomalies are mainly north of the equator across northern Indonesia and the western Pacific Ocean. The MJO is expected to remain weak for the next 1-2 weeks. Potential benefits/hazards in the global tropics, however, still include an enhanced chance of tropical cyclone development for weeks 1 and 2 in the Atlantic Basin and for week 1 in the eastern Pacific Basin. Currently, Typhoon Mawar and Tropical storm Guchol will impact areas in the northwest Pacific including Japan while Hurricane Hillary will affect the eastern Pacific Ocean. Meanwhile, above average rainfall is possible across areas of Central America, southern Mexico, and Florida as well as sections of the Caribbean Sea and the Gulf of Mexico during week 1. In addition, there is an increased chance of above average rainfall across west- central Africa during both weeks 1 and 2.