Weekly Tropical Climate Note

Issued 24 February 2015

Two severe tropical cyclones hit Australia

Over the past week, two severe tropical cyclones made landfall on the Australian coastline within hours of each other. Both storms crossed the coast on Friday 20 February. Severe tropical cyclone Lam made landfall on the north coast near the small town of Milingimbi in the Northern Territory at around 2:00 am (local time). Severe tropical cyclone Marcia made landfall on the central Queensland coast near 8:00 am (local time). This marks the first time in recorded history that two severe tropical cyclones crossed the Australian coast line on the same day.

The Madden-Julian Oscillation (MJO) has been weak or indiscernible in recent weeks and is not likely to have influenced tropical activity during this period. Rather, the recent increase in monsoonal weather and tropical cyclone activity in the Australian region is likely to have been influenced by a slow moving tropical disturbance, called an equatorial Rossby wave. These waves move slowly westwards and act to temporarily enhance tropical cloud and rainfall as they pass over a region. These waves often create a pair of low pressure circulations that form within the same longitude but on opposite sides of the equator.

Madden–Julian Oscillation likely to remain weak

Climate model forecasts for the MJO provide two possible scenarios for the coming weeks. The first, and most likely, scenario is that the MJO will remain weak or indiscernible for the next two weeks and hence will be unlikely to influence tropical weather patterns. The second scenario is that the MJO will gain strength over the Maritime Continent within the next seven to ten days, and therefore increase the chances of convection and tropical cyclone activity over the Australian region again.

See the Bureau's MJO Monitoring for more information.

El Niño–Southern Oscillation neutral

Sea surface temperatures across the tropical Pacific Ocean are neutral, having eased away from near–El Niño levels experienced late last year. The latest weekly NINO3.4 sea surface temperature anomaly is +0.43 °C and the 30 day SOI to 22 February is +0.8, the highest value since June 2014. Models indicate that tropical Pacific sea surface temperatures are likely to remain warm, but within the neutral range, until at least May. Several models suggest some warming may occur beyond May. However, model outlooks made in the first quarter of the year tend to be less reliable than those made at other times. This is because it is this time of year when ENSO events naturally decay. That said, all international models surveyed by the Bureau are consistent.

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

Next update expected by 17 February 2015 | Product Code IDCKGEW000

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