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 September 12, 2005

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

3. Overview • The MJO was weak during most of June, July, and August. During early September, however, the MJO has shown signs of becoming more active at moderate strength. • Currently, enhanced convection is located in the Indian Ocean, Indonesia, and sections of the far western Pacific while suppressed convection is located across much of the western Hemisphere. A distinct couplet of westerly (easterly) low-level wind anomalies in the Indian Ocean (far western Pacific) respectively indicate the MJO has strengthened. • The MJO is expected to remain moderately strong for the next 1-2 weeks. • During week 1, potential benefits/hazards in the global tropics associated with a stronger MJO signal include an increased chance of above (below) average rainfall across Indonesia / western Pacific Ocean (western Atlantic across Africa) due to the enhanced (suppressed) phases of an eastward propagating MJO. As a result of increased tropical convection in the Pacific Ocean (resulting in increased vertical wind shear in the Atlantic Basin) and large scale suppressed convection across the Atlantic sector there is an increased chance of below average tropical cyclone activity in the central Atlantic. On the other hand, an increased chance of above average tropical cyclone activity is expected in the western Pacific Ocean as a result of the eastward shifting MJO. Also, there is an increased chance of tropical cyclone activity across the eastern Pacific Ocean due to the enhanced phase of the MJO. • Other benefits/hazards during week 1, not specifically related to the MJO, include an increased chance of above average rainfall, strong winds, and greater than normal wave heights associated with Hurricane Ophelia across the eastern US coast. There is an increased chance of above normal rainfall in Northeast Brazil associated with low-latitude frontal system. • During week 2, an increased chance of above (below) rainfall across sections of Central America (southern Indonesia region), an increased chance of tropical cyclone activity in the Eastern Pacific ocean, and increased chance of below average tropical cyclone activity across the eastern Atlantic Ocean associated with the continued eastward propagation of the MJO. There is also a possibility of enhanced tropical cyclone activity in the Caribbean Sea.

4. 850-hPa Vector Wind Anomalies (m s-1) Note that shading denotes the magnitude of the anomalous wind vectors. Easterly anomalies in the eastern Pacific strengthened. Westerly anomalies in the Indian Ocean moved eastward and easterly anomalies in the western Pacific weakened slightly.

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). During June through early July, easterly anomalies dominated the western equatorial Pacific Time In early August, a period of westerly anomalies were evident in the western Pacific. Westerly anomalies developed in the Indian Ocean during the last two weeks and expanded eastward during the last several days. Easterly anomalies established in 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) Time The MJO was strong from late March through mid-May but has been very weak during June, July and August. Enhanced convection in the Indian Ocean propagates eastward and convectionin thewestern Pacific is evident during the last several days. 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) A period of enhanced convection north of the equator in the far western Pacific was evident during late July and early August. Time During mid-August, suppressed convection north of the equator stretched from Indonesia into the western Pacific. Near the end of August and beginning of September, enhanced convection north of the equator in the western Pacific. Longitude

8. Anomalous OLR and 850-hPa Wind: Last 30 days Enhanced convection developed in the E. Indian Ocean and W. Pacific during the last 10 days. Convection across the eastern Pacific weakened during the last 10 days.. Equatorial westerly anomalies in the Indian Ocean and easterly anomalies in the western Pacific during the last 10 days.

9. 200-hPa Velocity Potential Anomalies (5°S-5°N) Positive anomalies (brown shading) indicate unfavorable conditions for precipitation. Negative anomalies (green shading) indicate favorable conditions for precipitation. The MJO was weak in June and early July. Regions of upper level divergence and convergence were generally stationary. Weak eastward propagation of upper level convergence and divergence is evident from mid-July through August. Currently, upper-level divergence (convergence) is located in the Indian Ocean and western Pacific (western Hemisphere). Time Longitude

10. 200-hPa Vector Winds and Anomalies (m s-1) Note that shading denotes the magnitude of the anomalous wind vectors. Anti-cyclonic circulation in the south-western Indian Ocean behind enhanced convection. Large area of westerly anomalies in the Pacific along and south of the equator.

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. 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 become above average in the western Pacific during July, August, and early September. Time Longitude

12. MJO Index (Magnitude and Phase) The current state of the MJO as determined by an index based on Empirical Orthogonal Function (EOF) analysis using combined fields of near-equatorially-averaged 850 hPa zonal wind, 200 hPa zonal wind, and satellite-observed outgoing longwave radiation (OLR) (Wheeler and Hendon, 2004). The axes represent the time series of the two leading modes of variability and are used to measure the amplitude while the triangular areas indicate the phase or location of the enhanced phase of the MJO. The farther away from the center of the circle the stronger the MJO. Different color lines indicate different months. The MJO was weak during the months of June, July, and August. Recently in early September the MJO has strengthened with the enhanced phase located in the Maritime Continent or Indonesia region (phase 5).

13. Empirical Forecast Based on the Real-time Multivariate MJO index Moderate MJO activity is forecast to propagate from Indian Ocean across the maritime continent into the far western Pacific. for the next 6-10 day period.

14. Potential Benefits/Hazards –Week 1 2 6 4 5 3 1 7 6 Increased chance of above average rainfall across southern Indonesia and the far western Pacific Ocean Hurricane Ophelia will impact the east coast with above average rainfall, strong winds, and high wave heights Increased chance of below average rainfall from the eastern Atlantic across Africa Increased chance of below average tropical cyclone activity in the central Atlantic Increased chance of above average tropical cyclone activity in the eastern Pacific Ocean Increased chance of above average tropical cyclone activity in the western Pacific Ocean Increased chance of above average rain fall in northeast Brazil.

15. Potential Benefits/Hazards – Week 2 1 2 4 3 Increased chance of above average tropical cyclone activity across the eastern Pacific Ocean Increased chance of above average rainfall over Central America Increased chance of below average rainfall from the eastern Indian Ocean into the far western Pacific Ocean Increased chance of below average tropical cyclone activity across the eastern Atlantic Ocean

16. Summary • The MJO was weak during most of June, July, and August. During early September, however, the MJO has shown signs of becoming more active at moderate strength. • Currently, enhanced convection is located in the Indian Ocean, Indonesia, and sections of the far western Pacific while suppressed convection is located across much of the western Hemisphere. A distinct couplet of westerly (easterly) low-level wind anomalies in the Indian Ocean (far western Pacific) respectively indicate the MJO has strengthened. • The MJO is expected to remain moderately strong for the next 1-2 weeks. • During week 1, potential benefits/hazards in the global tropics associated with a stronger MJO signal include an increased chance of above (below) average rainfall across Indonesia / western Pacific Ocean (western Atlantic across Africa) due to the enhanced (suppressed) phases of an eastward propagating MJO. As a result of increased tropical convection in the Pacific Ocean (resulting in increased vertical wind shear in the Atlantic Basin) and large scale suppressed convection across the Atlantic sector there is an increased chance of below average tropical cyclone activity in the central Atlantic. On the other hand, an increased chance of above average tropical cyclone activity is expected in the western Pacific Ocean as a result of the eastward shifting MJO. Also, there is an increased chance of tropical cyclone activity across the eastern Pacific Ocean due to the enhanced phase of the MJO. • Other benefits/hazards during week 1, not specifically related to the MJO, include an increased chance of above average rainfall, strong winds, and greater than normal wave heights associated with Hurricane Ophelia across the eastern US coast. There is an increased chance of above normal rainfall in Northeast Brazil associated with low-latitude frontal system. • During week 2, an increased chance of above (below) rainfall across sections of Central America (southern Indonesia region), an increased chance of tropical cyclone activity in the Eastern Pacific ocean, and increased chance of below average tropical cyclone activity across the eastern Atlantic Ocean associated with the continued eastward propagation of the MJO. There is also a possibility of enhanced tropical cyclone activity in the Caribbean Sea.