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.
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
The 2024–25 northern wet season ends
Averaged across Australia, north of 26° S, the wet season (October 2024 to April 2025) rainfall was 566.9 mm, which was 21% above the 1961–1990 average of 476.4 mm. While area-averaged rainfall across the Northern Territory was close to the long-term average, Queensland and much of northern Western Australia observed above to well above-average rainfall between October and April. Large areas in Queensland and Western Australia saw rainfall in the highest 10% of the historical range (since 1900), with some areas recording their highest wet-season rainfall on record—notably, around the Townsville region of Queensland. For Queensland as a whole, the wet season rainfall was 711.8 mm, the eleventh-highest wet season rainfall on record, and wettest since 2010–11.
Early wet season rainfall was generally average to above-average before a very dry January (driest January since 1994 for northern Australia as a whole). Contributing to this was a late start to the monsoon onset observed at Darwin. The official monsoon onset date at Darwin was 7 February, the latest since records commenced in 1957–58, surpassing the previous latest onset date of 25 January (during the 1972–73 wet season). The usual Darwin onset date is around the last week of December. From February to April, area-averaged rainfall over northern Australia was above average.
Northern wet season temperatures
The mean maximum temperature for northern Australia's wet season was 36.3 °C, 1.61 °C above the 1961–1990 average, and the fifth-warmest on record since national observations started in 1910. The mean minimum temperature was 1.67 °C above the 1961–1990 average, and the warmest on record.
Virtually all regions across northern Australia observed both above-average maximum and minimum temperatures. Broad areas of northern Australia observed temperatures in the highest 10% of the historical range, with some areas also observing highest mean maximum and minimum temperatures on record for the wet season period.
Tropical cyclone season
There were 12 tropical cyclones (TCs) in the Australian region during the 2024–25 tropical cyclone season, just above the long-term average of 11 per year. This is the highest number since 2005–06 season which also had 12 TCs. Eight of the 12 cyclones this season were severe: Sean, Taliah, Vince, Zelia, Alfred, Bianca, Courtney and Errol. The others being Robyn (which formed in November), Dianne and two unnamed systems that were deemed to have reached cyclone intensity upon reanalysis: designated 09U and 25U.
Of the 12 TCs, 11 were in the western region and just one, Alfred, in the eastern region. This is the most in the western region since the 1999–2000 season. The 7 severe TCs in the western region is the highest number since the 1998–99 season. There were no TCs observed in the northern region, the first time this has occurred since 2020–21.
There were 5 tropical cyclones that impacted the Australian coast, with 4 systems making landfall. The most significant impact was from TC Alfred in early March, although Alfred had technically weakened to below-TC intensity at the time of landfall. Alfred generated large waves resulting in coastal erosion along a large part of the southern Queensland and northern New South Wales coasts, as well as heavy rainfall leading to flooding, and widespread wind impacts.
Only Zelia crossed the Australian coast as a severe TC, just east of Port Hedland on the Pilbara coast at category 4 intensity. Dianne crossed the Kimberley coast at category 2 intensity. Errol crossed the Kimberley coast just after weakening below TC strength. Sean did not cross the coast but caused a period of gales along the western Pilbara coast.
Dry season outlook for northern Australia
May marks the beginning of the northern Australian dry season. During this time, most of tropical northern Australia has very low rainfall. The long-range forecast for May to July, issued on 1 May, indicates below average rainfall is likely for much of northern Australia.
Warmer than average days and nights are very likely, with an increased chance of seasonal temperatures in the highest 20% of the historical range across nearly all parts of northern Australia.
The Bureau's climate model indicates neutral El Niño–Southern Oscillation (ENSO) conditions (neither El Niño nor La Niña) are expected to persist until at least September. This is consistent with a range of international models. These models also indicate a negative Indian Ocean Dipole may develop in late winter, although model accuracy is typically low at this time of year for forecasts beyond a month in advance. The Bureau's long-range forecasts are updated weekly.
Product code: IDCKGEW000
ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.
Product Code: IDCKGEM000
