Tropical Climate Update

Out-of-season tropical cyclone activity in South Pacific Ocean

Although the southern hemisphere tropical cyclone season officially ended on 30 April, tropical cyclone activity persisted in the South Pacific Ocean during early May. Record high sea surface temperatures in the region are likely to have contributed to this out-of-season activity.

Tropical cyclone Ella, which formed near American Samoa on 9 May, tracked in a westerly direction and reached category 2 strength – with estimated 10-minute mean winds of 110 km/h – before being downgraded to a tropical low on 14 May. Impacts associated with this system were relatively minor, however heavy rainfall was reported, including a 24-hour total of 263 mm at Apia, Samoa.

Severe tropical cyclone Donna also affected the region from 3-10 May. Donna was an unusually intense system for May, reaching category 5 strength, with mean winds to an estimated 205 km/h – making it the most intense southern hemisphere system recorded at this time of year. Reports of damage associated with Donna were mostly confined to far northern parts of Vanuatu.

Dry-season conditions across northern Australia

Conditions typical of the northern Australia dry season – which officially commenced on 1 May – have generally become established in the last fortnight. Observations of tropical winds shows a stark transition from a westerly wind flow across Australian longitudes from November to April – typical of wet-season conditions – to an easterly flow in May, which is the dominant wind regime during the dry season.

Local weather conditions and intraseasonal variability can see periods when dry-season conditions temporarily cease across parts of northern Australia. The predicted rainfall event for the Queensland central coast later this week, generated by a combination of low-level moisture and a strong upper-level trough over the region, is an example.

Madden Julian Oscillation

While the effect of the Madden-Julian Oscillation (MJO) on northern Australia lessens during the dry-season months when rainfall is typically very low, the MJO can still have a significant impact across the broader Maritime Continent to Australia’s north. Internationally, at this time of year, the strength and position of the MJO becomes a significant influence on the onset of the Indian Monsoon, which typically occurs at Kerala (southern India) in early June.

Currently, a weak to moderate MJO signal is apparent in the western Indian Ocean. Most climate models indicate the signal will continue its eastwards propagation across the Indian Ocean.

For more information on the MJO, see the Bureau's current MJO monitoring information.

El Niño WATCH continues

Although the El Niño-Southern Oscillation (ENSO) is currently neutral, there remains a possibility that El Niño will develop during the second half of 2017. Hence, the Bureau's ENSO Outlook status remains at El Niño WATCH. This means the likelihood of El Niño forming in 2017 is approximately 50% (twice the climatological average).

See the Bureau’s ENSO Wrap-Up for official El Niño, La Niña and Indian Ocean Dipole information.