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 and current conditions
During the week ending 13 April, isolated showers and thunderstorms affected Queensland's north-eastern coast, parts of the Top End of the Northern Territory and areas in northern and central Western Australia. The highest weekly totals of up to 50 mm, and locally higher, were recorded in northern and western areas of the Top End.
Riverine flooding in central Australia continues to recede slowly with a moderate flood warning current for the Eyre Creek.
Weekly maximum temperatures were above average across much of northern Australia, with maximum temperature anomalies up to 4 °C above average across most of the tropical north. Weekly minimum temperature anomalies were below average for much of the eastern tropics and above average for western parts of tropical Australia.
Severe Tropical Cyclone Maila
Tropical low 37U formed on 2 April in the Solomon Sea, between Papua New Guinea (PNG) and the Solomon Islands. It slowly intensified while remaining relatively stationary and on 4 April reached the tropical cyclone (TC) intensity and was named TC Maila by the PNG National Weather Service. Maila intensified into Severe TC system (Category 3) early on 6 April and later in the day it entered the Australian Area of Responsibility (AOR). Severe TC Maila continued to move slowly, intensifying into a Category 5 system early on 8 April. From 9 April, Maila started to weaken due to the interaction with land as it passed over Papua New Guinea. Early on 11 April, Maila weakened to a Category 1 system while remaining slow-moving in the Solomon Sea, and later in the day it was downgraded to a tropical low. Strong winds, heavy rainfall and high waves caused significant damage to parts of PNG's infrastructure, disruption to supply chains and landslides, including in Milne Bay Province and Bougainville.
Ex-TC Maila is forecast to track in the westerly direction across the Coral Sea towards the Far North Queensland coast and, combined with a low pressure trough, bring increased rainfall to northern Queensland and northern parts of the Northern Territory in the coming days.
Severe TC Maila was the 11th TC in the Australian AOR in the 2025–26 season and the 7th to reach Severe intensity.
Tropical low 38U
A weak tropical low (38U) is currently, as at 8 am AWST on 14 April, in the Indian Ocean just to the north of Cocos (Keeling) Islands. It is forecast to move to the west, passing to the north of Cocos (Keeling) Islands on 15 April without any direct impact to islands, and continue towards the western boundary of the Australian AOR. For the latest information on tropical activity, see our 7-day forecast.
Rainfall and temperature forecast
The forecast for the fortnight of 18 April to 1 May, issued 13 April, shows rainfall is likely to be above average for northern parts of Queensland and the Northern Territory. Rainfall is likely to be below average for much of southern tropical Australia. Maximum temperatures are likely to be below average for parts of northern Queensland and much of the Top End in the Northern Territory, and above average across remaining parts of the tropical Australia.
Madden–Julian Oscillation
A strong pulse of the Madden–Julian Oscillation (MJO) is currently located in the Western Pacific. Most models forecast the MJO to remain strong and progress into the Western Hemisphere and Africa region in the coming days. When located in these regions, the MJO enhances westerly wind anomalies over the western and central Pacific, which is likely to assist in El Niño development via warming of tropical Pacific sea surface temperatures. A MJO in the Western Hemisphere also typically reduces the likelihood of rainfall over parts of north-east Australia.
International Conditions
Severe Tropical Cyclone Vaianu
Tropical Cyclone (TC) Vaianu formed on 5 April near Fiji. It rapidly intensified and on 7 April reached a severe TC intensity (Category 3 system) while passing west of Fiji where it brought heavy rainfall, strong winds and high seas. Severe TC Vaianu tracked southwards weakening over the cooler waters and transitioned into an extratropical cyclone on 9 April as it moved south of the Tropic of Capricorn. Ex-TC Vaianu continued to track in the southerly direction towards New Zealand where it made landfall on 12 April near the Maketu Peninsula in Bay of Planty. It tracked south-east across parts of the North Island before moving offshore. It brought heavy rainfall and damaging winds, resulting in flooding and power outages across parts of New Zealand's North Island, as well as hazardous coastal conditions.
Super Typhoon Sinlaku
A tropical storm, named Sinlaku, developed in the western North Pacific, east of Philippines, on 9 April. The storm rapidly intensified while moving to the west, and was upgraded to a typhoon on 11 April, the first typhoon of the 2026 season. Sinlaku continued a rapid intensification and on 12 April was upgraded to a violent typhoon (equivalent to Australian Category 5). As of 14 April, Sinlaku is currently tracking to the north-west across the Philippine Sea, towards the Northern Mariana Islands of Saipan and Tinian. Super Typhoon Sinlaku is forecast to bring heavy rainfall, a devastating storm surge and huge ocean swell to Guam and Northern Mariana Islands.
Product code: IDCKGEW000
ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.
Product Code: IDCKGEM000
