Weekly Tropical Climate Note

Issued on Tuesday 15 April 2014

Madden-Julian Oscillation forecast to weaken

This past week saw active tropical convection near the equator from Indonesia through to the central Pacific, including northern Queensland. In the northern hemisphere, tropical storm Peipah brought heavy rainfall to the Philippines, while in the southern hemisphere tropical cyclone Ita impacted on northern Queensland. Tropical moisture from the Indian Ocean was drawn inland over Australia's central deserts, during the week, bringing heavy rainfall to northwest, central and southern Australia.

The Madden-Julian Oscillation (MJO) has been an active contributor to enhanced tropical convection across the Asia-Pacific region this week. However, most climate models predict the MJO will weaken later this week as it enters the western Pacific region, thus lessening its impact on tropical weather. As the MJO moves away from Australia and weakens, northern Australia is likely to transition into a more dry season-like weather pattern.

See the Bureau's MJO Monitoring for more information on location and tracking of the MJO.

El Niño likely to develop

While the Pacific is currently in a neutral state, recent changes across the Pacific and climate model forecasts indicate an El Niño is likely to develop in the coming months. El Niño is often, but not always, associated with below normal rainfall across large parts of southern, eastern and northern Australia during the second half of the year.

El Niño is a natural part of the global climate system. It occurs when the ocean surface temperatures in the central and eastern tropical Pacific Ocean change from a neutral ('normal' or 'average') state to a warmer than normal state for several seasons. Changes in sea surface temperature in the Pacific Ocean are commonly measured across several regions. The latest sea surface temperature anomaly across the NINO3.4 region, in the central Pacific, is +0.3 °C and has shown steady warming since February.

The Southern Oscillation is the atmospheric response to the changing ocean. During El Niño, it is common for areas of active tropical weather to shift east toward Tahiti and coincide with the region of warmer sea surface temperatures while northern Australia sees less tropical activity. Hence, the Southern Oscillation Index (SOI) is measured as the difference in mean sea level pressure between Tahiti and Darwin, Australia. The latest 30–day average SOI value to 13 April is −4.3; a sustained value of less than −8 usually indicates an El Niño.

Climate scientists often describe the oceanic and atmospheric components of this phenomenon together as the El Niño—Southern Oscillation, or ENSO. Learn more about ENSO or read the Bureau's ENSO Wrap-Up for official information about the current ENSO state and to learn more about how ENSO can affect Australia.

Next update expected by 22 April 2014| Product Code IDCKGEWOOO

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