Weekly Tropical Climate Note

Issued 26 May 2015

Unseasonal rainfall for Australia's north coast

A short burst of wet weather is expected over the north coast of Australia's Top End this coming weekend, even though northern Australia is well into the dry season. A weak trough which extends over the Arafura Sea is forecast to deepen and shift toward the southwest over the coming days. While there is still some uncertainty as to the strength and location of the trough, it is possible that it will dip far enough south to create showers and storms along the north and northwest coasts of the Top End.

Rain in May over northern Australia is not unprecedented, and the current synoptic set-up is a common cause of May rainfall. Darwin Airport, for example, records two rain days on average in May and sees a rainfall event of more than 10 mm about once every other May.

Southwest Indian Monsoon

Temperatures over the Indian subcontinent have increased recently ahead of the southwest Indian monsoon, with severe heatwave conditions reported to be impacting in large parts of the country. A southwesterly surge of wind has pushed into the Bay of Bengal and is advancing toward the northwest. According to the Indian Meteorological Department the onset of the annual monsoon at Kerala is expected within the coming week. This signals the arrival of the monsoon over the Indian subcontinent and represents the beginning of the rainy season over the region.

The Madden-Julian Oscillation (MJO) is often a major driver of monsoonal variability. However, for the past five weeks it has been weak or indiscernible and is unlikely to have contributed to the current monsoonal flow over the Bay of Bengal. A strong shift in the cloud and wind patterns due to El Niño can make an MJO signal difficult to detect. Forecasts for the MJO show a great deal of uncertainty in the strength, position, and progression of the MJO in the coming weeks. Most indicating the MJO will remain weak, although some models indicate a strengthening over the western hemisphere over the coming week, which could act to enhance tropical activity over the western tropical Pacific.

See the Bureau's MJO Monitoring for current MJO information.

El Niño strengthens

Large scale rainfall patterns across the tropics are consistent with the developing El Niño in the Pacific Ocean. Cloudiness and rainfall near the dateline and across the central Pacific has been enhanced for several weeks, while tropical activity over the Maritime Continent region for the same period has been suppressed. The latest 30–day Southern Oscillation Index value is −17.4 to 24 May. Climate models monitored by the Bureau indicate the tropical Pacific Ocean will continue to warm over the coming months.

See the Bureau of Meteorology's ENSO Wrap-Up for official El Niño information.

Next update expected by 2 June 2015 | Product Code IDCKGEW000

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