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
Australian region
Recent conditions
For the fortnight ending 24 August, maximum temperatures across northern Australia were generally up to 4 °C above average, except for southern parts of the Northern Territory extending into Western Australia and coastal parts of north-eastern Queensland where maximum temperatures were up to 2 °C below average.
Minimum temperatures for the fortnight ending 24 August were generally 2 to 4 °C above average with minima reaching up to 8 °C above average for eastern parts of Western Australia, western parts of the Northern Territory, and the Territory's south-east extending into Queensland. Minimum temperatures were below average for small areas in eastern and central Queensland.
For the fortnight ending 24 August, there was little to no rainfall across most of northern Australia. However, parts of the southern Northern Territory, Western Australia's interior and north-eastern coastal Queensland, recorded up to 50 mm during the fortnight.
Long-range forecast
The long-range forecast for September to November, issued on 20 August, indicates above average rainfall is likely for much of the western half of northern Australia, extending into north-western Queensland, and below average rainfall is likely along parts of the eastern coastal fringe and Cape York Peninsula in Queensland. This season marks northern Australia's transition to the wet season. Early in the season, rainfall often remains low across much of the north, with less than 10 mm typically recorded in September.
Maximum temperatures for September to November are likely to be above-average across the southern half of northern Australia, and below average for north-eastern areas of tropical Queensland and the northern Kimberley in Western Australia. Minimum temperatures are likely to be above average across most of northern Australia.
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 and for parts of the north-west coastline, but an earlier onset is mostly favoured elsewhere across northern Australia.
Madden–Julian Oscillation
The Madden–Julian Oscillation (MJO) is currently weak or indiscernible. Forecasts as at 22 August show it is most likely to remain weak over the coming fortnight.
Tropical wind and cloudiness have been strongly influenced by El Niño since May, with westerly winds and increased cloudiness dominating the western to central tropical Pacific, and decreased cloudiness across the Maritime Continent.
International Conditions
Heavy rainfall in Japan and South Korea
On 13 August, eastern Japan, particularly the Chiba Prefecture, experienced a heavy rainfall event. Chiba City observed a daily total of 367.0 mm, three times its average August rainfall, with 115 mm recorded in one hour. The rainfall caused extensive urban flooding, landslides, power outages and transport disruptions with reports of fatalities. This event was driven by highly unstable atmospheric conditions that resulted in thunderstorms and intense convective rainfall.
Between 15 and 17 August, a low-pressure system directed moist air from the East China Sea towards South Korea bringing heavy rainfall especially to the country's south. Some areas in the south-east had three-day rainfall totals up to 800 mm (approximately 90% of the region's July-August average rainfall). Heavy rainfall resulted in flooding, landslides and transport disruptions. This event was associated with abundant tropical moisture from remnants of typhoons Dolphin and Chan-hom.
Typhoon Saudel
Typhoon Saudel (Obet) developed on 19 August east of the Philippines and rapidly intensified to typhoon strength by 21 August. It is forecast to continue tracking north-westwards across the Philippine Sea and strengthen further as it passes north of Taiwan.
Tropical Storm Narra
A slow-moving tropical depression over the Gulf of Tonkin intensified into tropical storm Narra on 21 August and continued to strengthen over the subsequent days. By 24 August, it was about 150 km east of Hai Phong, Vietnam, affecting northern Vietnam and south-eastern China. Narra is forecast to make landfall in southern Guangxi, China, on 27 August, then gradually weaken into a tropical depression. The system caused widespread heavy rainfall, flooding, landslides and property damage across northern Vietnam as well as flooding in China's coastal areas.
Product code: IDCKGEW000
ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.
Product Code: IDCKGEM000
