Tropical monitoring and outlooks
Madden-Julian Oscillation (MJO)
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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.
Tropical atmospheric waves
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.
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.
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.
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.
Download data: RMM Data
*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.
These maps show average minimum or maximum temperature anomalies for each of the 8 MJO phases. Red-yellow colours indicate higher than normal temperature, while blue colours indicate lower than normal temperature.
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.
Outgoing longwave radiation (OLR) is often used as a way to identify tall, thick, convective rain clouds. These maps show the difference from expected cloudiness based on the position of the MJO. The violet and blue shading indicates higher than normal, active or enhanced tropical weather, while orange shading indicates lower than normal cloud or suppressed conditions.
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
These maps show the atmospheric troughs and ridges (in blue and red, respectively) associated with the different phases of the MJO at the 500hPa level. The 500 hPa level is approximately 5500 m above sea level and is about the middle of the troposphere. Colour shading is only used where the geopotential height anomalies are determined to be statistically-significant at the 5% level.
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
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.
OLR totals over the dateline
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
Westerly wind anomalies
Australian region
Recent conditions
For the week ending 22 December, hot and humid conditions resulted in daily thunderstorms and showers across much of the tropical north, tropical low 07U generated heavy rainfall in some areas around the Gulf of Carpentaria (see section below for details on tropical low 07U), while onshore airflow brought rainfall to Australia's north-east.
Weekly rainfall totals of 100 mm to more than 200 mm were recorded in parts of the southern Gulf of Carpentaria coast and adjacent inland areas, and totals of 15 to 100 mm, locally higher, were recorded in northern parts of Western Australia, much of northern and eastern Northern Territory and large parts of Queensland. The highest weekly total was 343.2 mm at Mornington Island Airport (Queensland), and the highest daily total was 148.0 mm at Centre Island (Northern Territory) in the 24 hours to 9 am on 20 December.
During the week, low-intensity to severe heatwave conditions started to develop across southern parts of the Northern Territory extending into Western Australia.
Maximum temperatures were below average across large parts of northern Australia on most days during the week. Daily maximum temperature anomalies were up to 4 °C below average across large parts of the tropics, with some localised areas up to 8 °C below average on some days.
Fortnightly forecast
The forecast for the fortnight of 27 December to 9 January, issued on 22 December, shows rainfall is likely to be above average for most of tropical Western Australia, the Top End in the Northern Territory and far north of the Cape York Peninsula in Queensland. Rainfall is likely to be below average for parts of central Queensland.
Maximum temperatures are likely to be below average across northern parts of Western Australia and the Northern Territory, and much of central Queensland. Minimum temperatures are likely to be above average across most of Western Australia and the Northern Territory, and far north-eastern Queensland.
Madden–Julian Oscillation
The Madden–Julian Oscillation (MJO), as of 20 December, is weak or indiscernible. Most forecasts from surveyed models suggest that over the coming week the MJO is likely to remain weak. Beyond the first week of January, there is little agreement as to how the MJO will develop.
Australian monsoon onset
Monsoonal conditions are developing over the southern Indian Ocean and across Australian longitudes. Conditions are currently relatively weak over northern Australia but expected to strengthen in the coming days. There is a high probability that the official onset of the Australian Summer Monsoon (measured at Darwin) will occur in the next day or two.
The Top End of the Northern Territory and regions adjacent to the Gulf of Carpentaria are most likely to observe the strongest monsoon conditions during this current active monsoon burst, which is expected to weaken by early January.
Severe Tropical Cyclone Bakung
Tropical low 05U formed on 11 December to the west of Sumatra, strengthened rapidly reaching tropical cyclone intensity on 12 December and was named Bakung. On 14 December, Bakung peaked at category 3 intensity (Severe Tropical Cyclone) as it moved into the north-west corner of Australia's Area of Responsibility tracking west-south-westwards. Bakung started to weaken on 15 December while changing direction of movement and was downgraded to a tropical low late on 17 December. On 18 December, ex-Tropical Cyclone Bakung left the Australia's Area of Responsibility while slowly dissipating. It did not have any direct impact on the Cocos (Keeling) Islands.
Tropical Cyclone Grant
A tropical low 03U started developing in the Timor Sea from 11 December, before tracking south-westward into the Indian Ocean staying well to the north-west of Western Australia's Pilbara coast. Moving westward it passed to the south of Christmas Island on 20 December bringing heavy rainfall to the island. 03U continued to slowly intensify, reached a tropical cyclone strength (Category 1) on 23 December and was named Grant. Tropical Cyclone Grant continued to move westward and is expected to intensify into a Category 2 system and pass close to the Cocos (Keeling) Islands later on Christmas Eve or during Christmas Day.
Tropical low 07U
Tropical low 07U started to develop in the northern Arafura Sea on 15 December. It moved slowly south towards northern Australia and approached the north-east Top End coast (Northern Territory) on 18 December, bringing increased shower and storm activity. 07U continued to move southward towards the southern Gulf of Carpentaria coast and on 20 December, it crossed the coast between Port Roper and Port McArthur (Northern Territory). 07U brought heavy rainfall to the coastal and adjacent inland areas of the Carpentaria (Northern Territory) and Gulf Country (Queensland) districts. The highest daily rainfall total during this event was 148.0 mm at Centre Island (Northern Territory) in the 24 hours to 9 am on 20 December.
International conditions
The negative Indian Ocean Dipole (IOD) event, which was active since August 2025, has ended with the IOD index now back to neutral levels (between -0.4 °C and +0.4 °C). The Bureau's model predicts the IOD is likely to remain neutral until at least the end of autumn 2026.
La Niña continues in the tropical Pacific. Forecast models indicate a return to ENSO-neutral conditions is likely in early 2026.
See the Southern hemisphere monitoring page for details of the current La Niña event.
Product code: IDCKGEW000
ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.
Product Code: IDCKGEM000
