Madden/Julian Oscillation: Recent Evolution, Current Status and Forecasts Update prepared by Climate Prediction Center / NCEP May 17, 2005

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

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 during mid-April associated with this MJO activity do not appear to have extended far enough east to initiate another Kelvin wave. The MJO has weakened and become less coherent during the past week. The convective phase of the MJO is contributing to enhanced convection across South America/Central America and the Caribbean while suppressed convection is influencing eastern Africa and the Indian Ocean. Based on the latest evolution of the MJO and statistical model forecasts, it is likely during the next week that enhanced convection will continue to impact the western hemisphere and suppressed convection can be expected in the Indian Ocean. Impacts in the global tropics include the chance of above average rainfall across northern South America and southern central America into the Caribbean (week 1) with drier than average conditions across the eastern Africa, the Indian Ocean and Indonesia (week 1). Due to the current uncertainty of the MJO, any impacts in the global tropics during week 2 are unclear.

850-hPa Vector Wind Anomalies (m s -1 ) Note that shading denotes the magnitude of the anomalous wind vectors. Easterly anomalies in the western Pacific have weakened during the last five days.

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). Westerly anomalies developed over the western equatorial Pacific in early January and persisted through February. Easterly anomalies in the western Pacific have weakened while weak westerly anomalies extend across the Indian Ocean into Indonesia.

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. The MJO has been strong since late March. Enhanced convection has shifted east into Indonesia but has weakened. Suppressed convection is evident in Africa and the Indian Ocean.

Anomalous OLR and 850-hPa Wind: last 30 days Positive OLR anomalies (below- average rainfall) developed over Indonesia during the middle of the period. These positive anomalies have weakened during the first 10 days of May. Low-level (850-hPa) westerly wind anomalies (m/s) observed over Indonesia and the western equatorial Pacific have weakened during mid to late April. Strong easterly anomalies are evident during the last ten days.

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 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. Currently, upper-level divergence is evident in Indonesia. Time

200-hPa Vector Winds and Anomalies (m s -1 ) Note that shading denotes the magnitude of the anomalous wind vectors. Equatorial upper-level wind anomalies across the eastern Indian Ocean, Indonesia, and the western Pacific have become weak.

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 and reached the South American coast during early April. Heat content has returned to near average in the western and central Pacific. Heat Content Evolution in the Eq. Pacific Longitude Time

Enhanced convection associated with the MJO in Indonesia and the western Pacific is forecast to dissipate early in the period while suppressed convection is expected to shift east from the Indian Ocean into Indonesia during the next 1-2 weeks. Empirical Forecast Based on the Real-time Multivariate MJO index

Potential Global Impacts –Week 1 (1) Increased chance of drier than average conditions stretching from central Africa to Indonesia. (2) Increased chance of above average rainfall across northern South America/southern Central America, and the Caribbean Sea 1 2

Potential Global Impacts – Week 2 No impacts are expected

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 during mid-April associated with this MJO activity do not appear to have extended far enough east to initiate another Kelvin wave. The MJO has weakened and become less coherent during the past week. The convective phase of the MJO is contributing to enhanced convection across South America/Central America and the Caribbean while suppressed convection is influencing eastern Africa and the Indian Ocean. Based on the latest evolution of the MJO and statistical model forecasts, it is likely during the next week that enhanced convection will continue to impact the western hemisphere and suppressed convection can be expected in the Indian Ocean. Impacts in the global tropics include the chance of above average rainfall across northern South America and southern central America into the Caribbean (week 1) with drier than average conditions across the eastern Africa, the Indian Ocean and Indonesia (week 1). Due to the current uncertainty of the MJO, any impacts in the global tropics during week 2 are unclear.