Tropical monitoring and outlooks
Madden-Julian Oscillation (MJO)

The Madden-Julian Oscillation (MJO) is the major fluctuation in tropical weather on weekly to monthly timescales. The MJO can be characterised as an eastward moving 'pulse' of cloud and rainfall near the equator that typically recurs every 30 to 60 days.


Forecast MJO location and strength

The chart shows the strength and progression of the MJO through 8 different areas along the equator around the globe.
Area 3 is north west of Australia, 4 and 5 are to the north (the Maritime Continent), and 6 is to the north east.

RMM1 and RMM2 are mathematical methods that combine cloud amount and winds at upper and lower levels of the atmosphere to provide a measure of the strength and location of the MJO. When this index is within the centre circle the MJO is considered weak. Outside of this circle the index is stronger and will usually move in an anti-clockwise direction as the MJO moves from west to east.


Select to see full-size map of MJO phase, updated daily.
Madden–Julian Oscillation (MJO) outlook phase chart

 

Tropical atmospheric waves

Madden–Julian Oscillation
Kelvin wave
Equatorial Rossby wave
MRG wave
Tropical atmospheric wave maps

About tropical atmospheric waves

MJO

The Madden–Julian Oscillation (MJO) is the major fluctuation in tropical weather on weekly to monthly timescales. It can be characterised as an eastward moving pulse or wave of cloud and rainfall near the equator that typically recurs every 30 to 60 days.

Other tropical waves in the atmosphere

In addition to the MJO, other large-scale atmospheric waves also occur in the tropics. The main ones are the convectively-coupled Kelvin wave (KW), equatorial Rossby wave (ER), and mixed Rossby-Gravity wave (MRG). They can provide further insight into the current tropical weather, such as the location and development of tropical cyclones, and what may occur over the coming days to weeks. These waves occur year-round, but typically have a greater influence on tropical weather in the Australian region during the wet-season months of October to April.

Kelvin wave (KW)

Equatorial Kelvin waves are alternating low and high pressure centres along the equator that move from west to east. For consistency with the theoretical structure of Kelvin waves, convection (leading to cloudiness and rainfall) near the equator should be on the western side of the low pressure regions. In contrast, clear conditions should be found on the eastern side of the low pressure. Like other atmospheric tropical waves, alternating zones of cloudiness and clear weather can be seen on satellite imagery in association with an active Kelvin wave. The waves move in the same direction as the Madden–Julian Oscillation, from west to east, but typically 2 to 3 times faster.

Per figure caption
Schematic depiction of the theoretical solution for an equatorial Kelvin wave in a dry, incompressible atmosphere

Equatorial Rossby (ER) wave

In theory there are several different equatorial Rossby waves. The most commonly seen atmospheric ER wave, and the one we discuss here, has high and low pressure regions centred at latitudes about 10 degrees north and south of the equator. To be consistent with theory, the lows and highs should form a symmetric pattern about the equator. Due to the wind flow around these high and low pressure regions, some regions along the equatorial zone favour cloud and rain formation, while other regions favour stable, clear conditions. On satellite imagery equatorial Rossby waves can often be identified due to the presence of cloud systems at similar longitudes on both sides of the equator. These cloud systems, in conjunction with the off-equatorial low pressure, can be the precursors to tropical cyclones on either side of the equator. While equatorial Rossby waves move at a speed close to that of a typical Madden–Julian Oscillation pulse, they move in the opposite direction—from east to west.

Per figure caption
Schematic depiction of the theoretical solution for an equatorial Rossby wave in a dry, incompressible atmosphere. Only one wavelength is drawn here.

Mixed Rossby-Gravity (MRG) wave

Like equatorial Rossby waves, mixed Rossby-Gravity waves also move towards the west, but MRG waves have their pressure centres arranged anti-symmetrically on either side of the equator. This means a low pressure centre on one side of the equator will be opposite a high pressure centre in the other hemisphere. Satellite analysis of mixed Rossby-Gravity waves shows favoured zones for deep convection, often with thunderstorm clusters, in an antisymmetric arrangement about the equator. Their speed of movement to the west is faster than that of an ER wave.

Per figure caption
Schematic depiction of the theoretical solution for a mixed Rossby-gravity wave in a dry, incompressible atmosphere (upper) and with moist convection (lower)

Images are from The COMET® Program, from Introduction to Tropical Meteorology.
The COMET® Website is at http://meted.ucar.edu/ of the University Corporation for Atmospheric Research (UCAR), sponsored in part through cooperative agreement(s) with the National Oceanic and Atmospheric Administration (NOAA), U.S. Department of Commerce (DOC). © 1997–2021 University Corporation for Atmospheric Research. All Rights Reserved.

MJO location and strength

These graphs show the strength and progression of the MJO through 8 different areas along the equator around the globe.
Area 3 is north west of Australia, 4 and 5 are to the north (the Maritime Continent), and 6 is to the north east.

RMM1 and RMM2 are mathematical methods that combine cloud amount and winds at upper and lower levels of the atmosphere to provide a measure of the strength and location of the MJO. When this index is within the centre circle the MJO is considered weak. Outside of this circle the index is stronger and will usually move in an anti-clockwise direction as the MJO moves from west to east.

MJO phase diagram
MJO phase diagram

*Note: There are missing satellite observations from 16/3/1978 to 31/12/1978.
Methodology: Until the end of 2013 we use the exact method of Wheeler and Hendon (2004, https://doi.org/10.1175/1520-0493(2004)132%3C1917:AARMMI%3E2.0.CO;2) and from 2014 we use the modified method of Gottschalck et al. (2010, https://doi.org/10.1175/2010BAMS2816.1).

Average weekly rainfall probabilities

These maps show average weekly rainfall probabilities for each of the 8 MJO phases. Green shades indicate higher than normal expected rainfall, while brown shades indicates lower than normal expected rainfall.

Select the 'Wind' checkbox to also show the expected 850 hPa (approximately 1.5 km above sea level) wind anomalies. The direction and length of the arrows indicate the direction and strength of the wind anomaly. The darker the arrow, the more reliable the information is.

The relationship of the MJO with global weather patterns changes with the season.
Read more: The Combined Influence of the Madden–Julian Oscillation and El Niño–Southern Oscillation on Australian Rainfall.

Maps of total and anomaly outgoing longwave radiation (OLR)

Global maps of outgoing longwave radiation (OLR)

Global maps of outgoing longwave radiation (OLR) highlight regions experiencing more or less cloudiness. The top panel is the total OLR in Watts per square metre (W/m²) and the bottom panel is the anomaly (current minus the 1979-1998 climate average), in W/m². In the bottom panel, negative values (blue shading) represent above normal cloudiness while positive values (brown shading) represent below normal cloudiness.

Tap boxes to view a timeseries graph of cloudiness for that region
image/svg+xml Southern India and Sri Lanka Southern India and Sri Lanka Indochina Indochina Philippines Philippines Malaysia and Indonesia Malaysia and Indonesia Guam and Marianas Guam and Marianas Micronesia Micronesia Northern Australia Northern Australia Coral Sea Coral Sea Vanuatu Vanuatu Fiji Fiji New Guinea New Guinea Solomon Islands Solomon Islands Nauru and Tuvalu Dateline Dateline

OLR totals over the dateline

OLR totals over the dateline (area at far right in region map above)

Regional maps of outgoing longwave radiation (OLR)

The graphs linked to this map show the OLRs for the different regions within the Darwin RSMC area. The horizontal dashed line represents what is normal for that time of year (based on the 1979 to 1998 period). The coloured curve is the 3-day moving average OLR in W/m². Below normal OLR indicates cloudier than normal conditions in this particular area, and is shown in blue shading. Above normal OLR indicates less cloudy conditions and is shown in yellow shading.

Time longitude plots

Time longitude plots of daily averaged OLR anomalies (left) and 850 hPa (approximately 1.5 km above sea level) westerly wind anomalies (right) are useful for indicating the movement of the MJO.

How to read the Time longitude plots

The vertical axis represents time with the most distant past on the top and becoming more recent as you move down the chart. The Horizontal axis represents longitude.

Eastward movement of a strong MJO event would be seen as a diagonal line of violet (downward from left to right) in the OLR diagram, and a corresponding diagonal line of purple in the wind diagram. These diagonal lines would most likely fall between 60°E and 150°E and they would be repeated nearly every 1 to 2 months.

Daily averaged OLR anomalies

Daily averaged OLR anomalies

Westerly wind anomalies

Westerly wind anomalies

Unseasonable rainfall over parts of southern Northern Territory

For the fortnight ending 13 July, rainfall totals greater than 25 mm were recorded in large parts of the southern Northern Territory and south-western Queensland, with totals locally exceeding 50 mm. These totals are notable as the average July rainfall for most of the southern tropics is less than 25 mm. Rainfall was produced during the passage of multiple upper-air troughs over the region.

Onshore airflow brought scattered showers to parts of north-east Queensland coast on many days, resulting in fortnightly rainfall totals greater than 50 mm. Most of remaining tropical Australia recorded little to no rain during the past fortnight.

Maximum temperatures for the fortnight ending 12 July were below average in parts of the southern Northern Territory extending into Western Australia, and up to 4 °C above average in northern parts of the Northern Territory and much of tropical Queensland. Minimum temperatures were generally up to 6 °C above average.

Long-range forecast

The long-range forecast for August to October, issued on 9 July, indicates that above average rainfall is likely for northern parts of Western Australia and adjacent parts of western Northern Territory. The likelihood is highest towards the end of the season, when rainfall over northern Australia is transitioning from the dry to the wet season. During August and September, most of the tropical north typically receives very little rainfall and low rainfall totals can be enough to exceed seasonal averages. The long-range forecast also indicates that above average rainfall is likely for eastern coastal fringe of Cape York Peninsula in Queensland and areas of eastern Top End in the Northern Territory.  Rainfall is likely to be below average for much of southern and central Queensland and the far north of the Northern Territory.

Maximum temperatures for August to October are likely to be above average for most of northern Australia, but below average for northern areas of tropical Queensland and the north-eastern Northern Territory. Minimum temperatures are likely to be above average across northern Australia.

Madden-Julian Oscillation (MJO)

The moderately strong pulse of Madden–Julian Oscillation (MJO) has been relatively stationary in the western Pacific over the past week. This pattern is likely a dominance of westerly winds in the western Pacific from the current El Niño pattern, rather than an active MJO pulse. Most models forecast this pattern to continue into late July.

Northern Rainfall Onset

The northern rainfall onset outlook provides probabilistic forecasts for the first significant rains after 1 September for the 2026–27 wet season. The northern rainfall onset for the 2026–27 season is likely to be later than normal for eastern and far northern parts of northern Australia, but earlier for most of the west. 

Tropical Storm Maysak

Tropical Storm Maysak formed on 2 July in the South China Sea and tracked north-westward towards Hainan, China, while slowly intensifying. Maysak made first landfall in Hainan Province on 3 July. After crossing Hainan, Maysak entered the Beibu Gulf, further intensified and was upgraded to a severe tropical storm. It made a second landfall on 4 July near the Vietnam-China border, weakened and was downgraded into a tropical depression. Maysak brought heavy rain, flooding and strong winds, resulting in some fatalities.

Maysak was the first tropical system to make landfall in mainland China this year. Although it was not an intense system by wind-speed standards, its slow movement and abundant moisture resulted in widespread flooding.

Violent Typhoon Bavi

Typhoon Bavi developed into a tropical storm on 2 July in the western Pacific Ocean, east of Philippines, then underwent a period of rapid intensification and on 4 July was upgraded to a violent typhoon (equivalent to Australian Category 5). Bavi tracked to the north-west across the Philippine Sea and on 6 July its centre passed just north of the US territorial island of Rota in the Northern Mariana Islands, bringing destructive winds, widespread heavy rain and flooding, and storm surges, impacting Guam and the Northern Mariana Islands Rota, Tinian and Saipan. Bavi continued in the north-westerly direction, towards south-eastern China, but started to gradually weaken and on 9 July was downgraded to typhoon intensity. Typhoon Bavi passed north of Taiwan on 11 July and made landfall on the eastern China's Zhejiang Province, bringing strong winds, heavy rain and flooding.

Indian monsoon onset

The 2026 Southwest Monsoon season has been characterised by a delayed and weak onset, with June rainfall across India nearly 40% below the climatological average. In July, the monsoon became more active and rapidly expanded across north-west India, and by 9 July the monsoon covered the entire country, one day later than the average date for full coverage of India. 

For more information about the India's Southwest Monsoon, go to the Monsoon Information Onset | India Meteorological Department.

Product code: IDCKGEW000

ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.

Product Code: IDCKGEM000

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