Weekly Tropical Climate Note

Very warm days for 2017 dry season so far

The northern Australia dry season commences in May and continues until the end of September each year. Apart from the east coast of tropical Queensland, this period sees generally dry conditions across most of northern Australia with many districts observing less than 50 mm, on average, of rainfall during the 5-month period.

Averaged across northern Australia, rainfall during the current dry season is tracking at less than half the long-term average as at the end of July. However, the more significant feature during 2017 has been the daytime temperatures. Northern Australia (the area north of 26°S, which is the southern border of the NT) experienced its highest mean daily maximum temperature for May to July since records began in 1910. The mean daily maximum temperature in 2017 was 1.93 °C above average for the May to July period (previous record was +1.46 °C in 2002).

The exceptional warmth has continued into August across much of northern Australia, particularly in Queensland and the Northern Territory where many sites are currently tracking well above average for maximum temperature. Further information on monthly and seasonal climate statistics can be found in the Bureau's climate summaries.

Overnight temperatures have also been warmer than average in many parts, but not as significantly as the daytime temperatures. At Darwin Airport, for example, the overnight minimum has dropped below 20 °C on only 25 nights so far this season—less than half of the dry-season average.

Tropical activity and flooding rains continue in northern hemisphere

The 11th tropical cyclone of the 2017 northwest Pacific cyclone season formed over waters to the northeast of the Philippines. Tropical storm Hato (Isang) is moving in a westerly direction towards southern mainland China, near Hong Kong. Hato (Isang) is predicted to strengthen marginally, but is not expected to become the fourth typhoon of the season in the northwest Pacific prior to landfall. Tropical cyclone activity to the end of August has been near-average (based on 1981–2010 climatology) for the number of named storms, but below the long-term average for typhoons (sustained winds of 118 km/h or greater; approximately seven typhoons). For information on tropical cyclone activity in the northwest Pacific region go to the website of the Japan Meteorological Agency.

This time of the year typically sees the Indian Southwest Monsoon at it northernmost extent. During September the monsoon normally starts its withdrawal across the Indian subcontinent, tracking gradually southwards before moving into the southern hemisphere during the Austral summer. So far, the subcontinent has seen near-average rainfall during this season's monsoon. The monsoon trough and an associated tropical low lies over northern India and has continued to generate widespread rainfall, which has led to extensive flooding in northeastern India, Nepal and Bangladesh. Reports indicate that more than a third of Nepal and Bangladesh have been flooded and over 16 million people have been affected across the three countries. Since the flooding and associated landslides commenced, more than 600 fatalities have been reported.

Madden–Julian Oscillation expected to strengthen

The Madden–Julian Oscillation (MJO) has remained weak and indiscernible for August so far. While not unanimous, most international climate models surveyed by the Bureau forecast the MJO signal to strengthen marginally in the coming seven days. Of these, the majority of models indicate that the MJO will re-develop over the Indian Ocean and track eastwards towards the Maritime Continent.

When the MJO moves over the Indian Ocean at this time of the year, cloudiness and rainfall is typically above average over the Indian Ocean, most of India, parts of South East Asia and the northern Maritime Continent region.

For northern Australia, rainfall is not significantly enhanced or suppressed under these circumstances, however overnight temperatures are typically above average across Queensland and parts of the eastern Northern Territory.

See the Bureau's current MJO monitoring for more information.

Product code: IDCKGEW000

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