Weekly Tropical Climate Note

Dry season conditions to ease slightly across northern Australia

For much of the last fortnight, northern Australia has been dominated by a significant southeasterly wind flow, due to a strong, slow-moving high-pressure system located near the Great Australian Bight. This situation has created classic northern dry-season conditions, marked by low humidity, below-average temperatures and a lack of rainfall. Temperature maps for the past week show the below average daytime and overnight temperatures experienced across nearly all of tropical Australia. Darwin Airport recorded seven consecutive nights where the temperature dropped below 20 °C—the equal-fourth longest run for the month of May in Darwin Airport's record. Humidity has been low across the region, and the only significant rainfall totals have been observed along the Queensland tropical east coast, a region which is typically the wettest part of northern Australia during the northern dry season.

In the coming week, the high pressure across southern Australia will move further east and weaken, leading to an easing of the cooler, drier southeasterly winds and a gradual increase in temperature across most northern regions. This is part of the typical dry-season pattern, whereby the conditions across northern Australia are strongly influenced by the prevailing zone of high pressure which moves across southern Australian latitudes at this time of the year.

See the Bureau's Climate Outlooks for long-range rainfall and temperature guidance.

Madden–Julian Oscillation expected to weaken over Indian Ocean

A moderate-strength pulse of the Madden–Julian Oscillation (MJO) currently lies over the western Indian Ocean. There is general agreement amongst international climate models that this MJO pulse will continue its eastwards progression, but weaken during the coming week. With the MJO over the Indian Ocean at this time of the year, rainfall patterns across northern Australia are not significantly affected and thus typical dry-season rainfall patterns are expected.

In the northern hemisphere over the past week, tropical cyclone Sagar took a rare, but not unprecedented, track into the Gulf of Aden, making landfall on northwestern Somalia with damaging winds in excess of 85 km/h and significant flooding. Rainfall patterns across the northern Indian Ocean and southern parts of the Indian subcontinent are likely to continue to be enhanced due to MJO activity in the coming week. Another monsoon depression has formed in the Arabian Sea and is forecast to impact Oman and Yemen later this week. The New Delhi RSMC is providing forecasts and warnings for this storm.

The MJO can help trigger the onset of the southwest Indian Monsoon. The Indian Meteorological Department (IMD) has observed that conditions are favourable for monsoonal development across the region. The IMD predicts that the official onset of the Indian monsoon at Kerala, in far southern India, will occur on 29 May (+/- 2 days)—close to the long-term average onset date of 1 June. Progress of the Indian monsoon can be followed here.

Across the Maritime Continent, non-MJO tropical wave activity has contributed to widespread thunderstorm activity, leading to above-average rainfall in some equatorial zones.

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