Analysis - Sea Surface Temperature Distributions 2010 v 2020 La Niña's

December 2010 Sea Surface Temperatures and rainfall deciles

Record warm sea surface temps around Australia’s north and the Maritime Continent

With the exception of a small strip, record rainfall through eastern Australia in that month

December 2020 Sea Surface Temperatures and rainfall outlook (21 Dec 2020 - 3 Jan 2021)

SSTs as of 11 December 2020 (tropicaltidbits.com)

Fortnightly precipitation forecast 21 Dec-3 January 2020 (courtesy BOM 10 December).

So what?

The La Niña signature can be clearly seen in both images, with cool water extending into the western Pacific Ocean. Models are anticipating the Coral Sea to warm and deliver rainfall to eastern Qld areas (although the latest 7-day change maps on tropicaltidbits.com would suggest otherwise). The waters around the Maritime Continent are not near as warm as 2010. The next research article suggests that we need these waters, and those to the east of Australia to be much warmer to supply rainfall events this summer - this warming may well happen in the next month or so.

Latest research - tracing the origins of moisture for precipitation

Mean moisture contribution to Australian precipitation in each season, with mean climatological low-level wind vectors.

A team of Australian climate researchers recently investigated the origin of moisture for regional precipitation and the relative importance of local versus remote processes. Where does our moisture leading to rain come from?

Knowing the long-term average regional source of moisture provides insight into the drivers of precipitation during anomalously dry or wet periods. In the case of drought, for example, identifying the long-term average source regions can help reveal whether the low precipitation was due to a reduction in source evaporation, anomalous atmospheric circulation or a lack of local precipitation generating mechanisms.

Key findings of the study;

• In summer, moisture for the Australian continent generally was primarily sourced from Australia’s Maritime Continent (waters around Philippines/Indonesia/Papua New Guinea)

• Summer precipitation in the Murray Darling Basin (MBD) was primarily sourced from the Tasman Sea, Southern Ocean and land within the basin itself.

• The MBD recycled more moisture from land sources for precipitation than any other eastern basin, with a maximum of 9.2% across the year.

• The Australian continent receives a minimum of 77% of moisture from marine sources in summer and a maximum of 89% in winter, with the remainder recycled from land sources.

• North-West Cloud Bands relating to the Indian Ocean Dipole interact with moisture from condensed moist air from the Tasman Sea to deliver precipitation to the MDB during spring.

What does all of this mean?

Coming into summer season, the distribution of warm waters around our perimeter does impact rainfall, although atmospheric processes involved to deliver that moisture is a whole other story!

We hope the land-sea interaction is captured in General Circulation Models, although it’s worthy of periodical monitoring the Sea Surface Temperatures in those areas identified by researchers and compare with other similar years.

Paper: Holgate, C.M., Evans, J.P., Van Dijk, A.I.J.M., Pitman, A.J. and Di Virgilio G. Australian Precipitation Recycling and Evaporative Source Regions (2020) Journal of Climate. https://doi.org/10.1175/JCLI-D-19-0926.s1

Monitoring heat waves this summer

About heat waves

Heatwaves are calculated using the forecast maximum and minimum temperatures over the next three days, comparing this to actual temperatures over the previous thirty days, and then comparing these same three days to the 'normal' temperatures expected for that particular location. Using this calculation takes into account people's ability to adapt to the heat. For example, the same high temperature will be felt differently by residents in Moree compared to those in Orange, who are not used to the higher range of temperatures experienced in Moree. The full forecast can be accessed here: http://www.bom.gov.au/australia/heatwave/

Nothing to speak of in terms of extreme heat in the coming week.

Heatwave forecast starting Monday 14 December through to Wednesday 16 December 2020

http://www.bom.gov.au/australia/heatwave/

9-day ECMWF rainfall outlook

Fresh today, the European ECMWF 9-day model shows rainfall deepening into desert areas of Western Australia with a weak pulse of the MJO now in Phase 5 in Australia’s north-west. The rainfall situation is set to become more interesting in the next fortnight as the MJO is anticipated to strengthen as it propagates further eastward towards the Pacific Ocean.

Refreshed multi-week models are consistently showing cool, wet conditions for NSW and Qld areas right through until 3 January 2021, so the La Niña might be turning up after all.

More details in next Fridays fortnightly analysis.

Access courtesy https://meteologix.com/au

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