Weekly Tropical Climate Note
Tropical activity increases to the north of Australia
A tropical low formed to north of the Solomon Islands on 13 April. Since then, it has slowly moved west over Papua New Guinea and into the Arafura Sea. The tropical low brought an increase in rainfall to southern parts of Papua New Guinea over recent days.
The Australian monsoon trough broke down on 11 April and is not expected to reform until next wet season. Instead of the tropical low being embedded within a monsoon trough, it is part of a weak equatorial Rossby wave that nearly mirrors a "twin" low in the tropical northern hemisphere east of the Philippines.
The tropical low over the Arafura Sea is forecast to continue west while slowly strengthening, and may cause heavy rainfall over Timor Leste in the coming days. Strong winds on the windward side of the ranges and rain bands associated with the tropical low increase the risk of flooding and landslides. A slight increase in rainfall over the northern part of the Northern Territory is also possible.
While the developing tropical low is unlikely to develop into a tropical cyclone, there is still a slight risk. For more information on any tropical cyclones affecting the Australian region, see the Bureau's current tropical cyclones warnings.
Madden-Julian Oscillation signal becomes weak again
After very briefly appearing over the western hemisphere, the Madden-Julian Oscillation (MJO) has become weak or indiscernible during the last week, and did not contribute significantly to tropical weather over the past week.
Most international climate models forecast an MJO signal to emerge over the western Pacific during the week, before moving east into the western hemisphere. However models show a large range of possible strengths from weak or indiscernible to moderately strong. An MJO signal over the western Pacific or western hemisphere at this time of year typically leads to a reduction in convective activity over the Maritime Continent and the tropical eastern Indian Ocean.
For more information on the MJO, see the Bureau's current MJO monitoring information.
El Niño WATCH remains as tropical Pacific sea surface temperatures warm
The El Niño-Southern Oscillation (ENSO) is currently neutral. Tropical Pacific sea surface temperatures (SSTs) have continued to warm since the start of the year. The Southern Oscillation Index (SOI) has been somewhat variable recently. Since the beginning of April, the SOI has returned to negative values, however it is still within neutral levels. Persistent values lower than -7 typically indicate El Niño conditions.
Climate model outlooks suggest the tropical Pacific Ocean will continue to warm over coming months, with most climate models predicting that SSTs in the NINO3.4 region will exceed El Niño thresholds during the second half of 2017. Over the past month, some climate models have reduced the likelihood of El Niño occurring. The Bureau's ENSO Outlook status remains at El Niño WATCH.
See the Bureau’s ENSO Wrap-Up for official El Niño, La Niña and Indian Ocean Dipole information.
Product code: IDCKGEW000