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
Recent conditions
In the past week, low pressure troughs and several embedded tropical lows brought heavy rainfall and widespread thunderstorms, some severe, across northern Australia and eastern Queensland, especially impacting far northern Queensland and the north-west of the Northern Territory.
In the latter part of the week, easterly onshore flow triggered severe thunderstorms and heavy falls across Queensland’s north tropical coast. A low-pressure trough brought moist tropical air to southern parts of the Northern Territory into northern South Australia, resulting in widespread rainfall.
For the week ending 16 March, weekly rainfall totals of 50 to 200 mm were recorded across much of northern Australia and parts of south-eastern Queensland. Locally higher falls exceeding 200 mm were recorded over Queensland's north tropical coast and parts of the Daly district in the Northern Territory. Warramunga (56 years of data) in the Northern Territory's interior observed a March daily rainfall record in the 24 hours to 9 am on 13 March of 105.7 mm. The highest weekly total (at a Bureau gauge) was 463.0 mm at Whyanbeel Valley in Queensland. The highest daily total (at a Bureau gauge) was 258.6 mm at Cairns Racecourse in Queensland in the 24 hours to 9 am on 15 March.
Widespread flooding continued in many catchments across the tropical north. In Queensland’s Gulf country, the Flinders River at Walkers Bend was above major flood level all week, as was the Northern Territory’s Daly River at Daly River Police Station; the latter site peaking on the 14th at 16.35 m, exceeding the previous record of 16.25 m set in 1998. Further rainfall during the week saw floodwaters rise and fall in Far North Queensland, around the Daintree.
There are currently many moderate to major flood warnings across eastern and central Queensland and eastern and northern catchments of the Northern Territory. For the latest flood advice, please visit warnings and alerts page.
Rainfall and temperature forecast
The forecast for the fortnight of 21 March to 3 April, issued 16 March, shows rainfall is likely to be above average across much of the tropical north. There is at least a 60% chance of rainfall being unusually high (amongst the wettest 20% of fortnights for this time of year) for the northern Cape York Peninsula in line with the forecast track of tropical low 34U. For parts of the interior, rainfall is likely to be below average for the fortnight.
Maximum temperatures are likely to be below average across most of northern Australia. Minimum temperatures are likely to be above average across most of eastern and northern Queensland, the eastern Top End and the Pilbara district in Western Australia. However, nights are likely to be below average for parts of the Kimberley and western parts of the Top End.
Tropical low 34U
As of 17 March, tropical low 34U lies to the south of the Solomon Islands and is forecast to become a tropical cyclone tonight. 34U is to move westwards during the week. There is increasing confidence that the system will strengthen and track towards and cross the northern Queensland coast late this week, before continuing into the Gulf of Carpentaria over the weekend. Please refer to the Tropical Cyclone 7-Day Forecast for the latest tropical cyclone forecast in the Australian region.
Madden–Julian Oscillation
As of 15 March, the Madden-Julian Oscillation (MJO) is currently moderate in the Western Pacific. Some models show the MJO is likely to exhibit a weak to moderate pulse in the Western Pacific in the coming week as it progresses towards the Western Hemisphere and Africa, before weakening later in March. When in the Western Pacific, the MJO can increase rainfall over northern Australia, particularly northern Queensland.
Product code: IDCKGEW000
ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.
Product Code: IDCKGEM000
