Madden/Julian Oscillation: Recent Evolution, Current Status and Forecasts Update prepared by Climate Prediction Center / NCEP September 19, 2005

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

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. Currently, enhanced convection is located across Southeast Asia, northern Indonesia and sections of the far western Pacific while suppressed convection is located across much of the Indian Ocean and Africa. Distinct couplets of westerly (easterly) low-level wind anomalies are evident first across Southeast Asia and then in the western Pacific Ocean and indicate an active MJO. The MJO is expected to remain weak to moderate for the next 1-2 weeks. During week 1, potential benefits/hazards in the global tropics associated with the MJO signal include an increased chance of above average rainfall across Central America, eastern Mexico, western Gulf Coast and Southeast Asia due to the enhanced phase of the MJO. On the other hand, an increased chance of below average rainfall exists across the eastern Indian Ocean and across Indonesia due to the suppressed phase of the MJO. Several areas of an increased chance of above average tropical cyclone activity are expected as a result of the current MJO signal. These include regions in the western Pacific, eastern Pacific, and the western Atlantic and Gulf of Mexico. In addition, Tropical cyclones Jova, Kenneth, Lidia, and Max will impact the central/eastern Pacific Ocean and Hurricane’s Philippe and Rita will affect the Florida Keys, Cuba, the Gulf of Mexico, and the western Gulf Coast during week 1. During week 2, there is an increased chance of above (below) average rainfall across west central Africa and the western Indian Ocean (the eastern Indian Ocean and Indonesia) associated with the continued evolution of the MJO. Also, although not highlighted on the slide 15, there is a possibility of above average rainfall across eastern areas of Southeast Asia, the Philippines and the far western Pacific and a elevated chance of tropical cyclone activity in the western Pacific. The uncertainty is high, however, in these regions during week 2.

850-hPa Vector Wind Anomalies (m s -1 ) Note that shading denotes the magnitude of the anomalous wind vectors. Anomalies in southern India, Bay of Bengal, and South China Sea due to northward summer-time propagation of convection associated with the MJO. Anomalies in the eastern Pacific associated with enhanced convection. Equatorial anomalies associated with the MJO moved to the western Pacific.

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 In late July and early August, a period of westerly anomalies were evident in the western Pacific. Westerly anomalies developed in the Indian Ocean during early September Anomalies associated with the MJO in the eastern Indian Ocean, Indonesia, and Pacific Ocean propagated eastward during the last two weeks.

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. Convection that developed near the beginning of September in the Indian Ocean propagates eastward and active convection during the last several days is located in the western Pacific.

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 mid-August, suppressed convection north of the equator stretched from Indonesia into the western Pacific. During late August and early September, enhanced convection north of the equator in the western Pacific.

Anomalous OLR and 850-hPa Wind: Last 30 days Convection across the east-central Pacific increased during the last 10 days. Easterly anomalies in the western Pacific and westerly anomalies in the equatorial Indian Ocean and Indonesia during the last 10 days. Enhanced convection developed in the Bay of Bengal, South China Sea, and the western Pacific during the last 10 days.

200-hPa Velocity Potential Anomalies (5°S-5°N ) Negative anomalies (green shading) indicate favorable conditions for precipitation. Positive anomalies (brown shading) indicate unfavorable conditions for precipitation. Longitude The MJO was weak in June. Regions of upper level divergence and convergence were generally stationary. Weak eastward propagation of upper level convergence and divergence is evident from July through August. Moderately strong upper level divergence developed in the Indian Ocean at the beginning of September and propagated eastward during the last two weeks. Time

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 southern Indian Ocean behind enhanced convection.

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. Heat Content Evolution in the Eq. Pacific Longitude Time

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. The MJO strengthened in early September. During the last week the MJO has weakened and is now located in the Maritime Continent and western Pacific (phases 5 and 6) regions.

Empirical Forecast Based on the Real-time Multivariate MJO index The convection in the Pacific associated with the MJO is forecast to remain weak over the next 1-2 weeks. An area of suppressed convection is forecast to develop in the Indian Ocean.

(1)Increased chance of above average tropical cyclone activity across the eastern Pacific Ocean (2)Increased chance of above average rainfall over Central America, eastern Mexico, western Gulf Coast (3)Increased chance of below average rainfall in the eastern Indian Ocean and across Indonesia (4)Increased chance of above average rainfall in Southeast Asia (5)Increased chance of above average tropical cyclone activity in the western Pacific Ocean (6)Increased chance of above average tropical cyclone activity in the Gulf of Mexico and western Atlantic Potential Benefits/Hazards – Week

Potential Benefits/Hazards –Week 2 (1)Increased chance of above average rainfall across west central Africa (2)Increased chance of above average rainfall western Indian Ocean (3)Increased chance of below average rainfall across the eastern Indian Ocean and Indonesia

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. Currently, enhanced convection is located across Southeast Asia, northern Indonesia and sections of the far western Pacific while suppressed convection is located across much of the Indian Ocean and Africa. Distinct couplets of westerly (easterly) low-level wind anomalies are evident first across Southeast Asia and then in the western Pacific Ocean and indicate an active MJO. The MJO is expected to remain weak to moderate for the next 1-2 weeks. During week 1, potential benefits/hazards in the global tropics associated with the MJO signal include an increased chance of above average rainfall across Central America, eastern Mexico, western Gulf Coast and Southeast Asia due to the enhanced phase of the MJO. On the other hand, an increased chance of below average rainfall exists across the eastern Indian Ocean and across Indonesia due to the suppressed phase of the MJO. Several areas of an increased chance of above average tropical cyclone activity are expected as a result of the current MJO signal. These include regions in the western Pacific, eastern Pacific, and the western Atlantic and Gulf of Mexico. In addition, Tropical cyclones Jova, Kenneth, Lidia, and Max will impact the central/eastern Pacific Ocean and Hurricane’s Philippe and Rita will affect the Florida Keys, Cuba, the Gulf of Mexico, and the western Gulf Coast during week 1. During week 2, there is an increased chance of above (below) average rainfall across west central Africa and the western Indian Ocean (the eastern Indian Ocean and Indonesia) associated with the continued evolution of the MJO. Also, although not highlighted on the slide 15, there is a possibility of above average rainfall across eastern areas of Southeast Asia, the Philippines and the far western Pacific and a elevated chance of tropical cyclone activity in the western Pacific. The uncertainty is high, however, in these regions during week 2.