Bruce Buckley from Weather Australia has compiled a special report for Doyle Sails on the unusual weather we are experiencing on the East Coast this Summer:
Sydney’s Unusual Summer Weather
It is no news for Sydney-siders that Sydney has had an unusual summer so far. There has been more rainfall than normal - Observatory Hill reported 138.8mm for January compared to the median
rainfall of 79.2mm - and there has been an absence of the strong NE sea breezes that have featured
in summers of the past. So why is this?
Much of the focus has been on the La Niña, which is a large scale phenomenon driven by sea surface
temperature anomalies across the Pacific Ocean. This oscillation has assisted in producing the
excessive rainfall and flooding being experienced across the NE of NSW and inland Queensland at
the moment.
However, this is only a part of the story. There is also a pool of cooler than normal water in the
central Tasman Sea and much warmer waters off the western and southern coastlines of Australia.
What this does is strengthen the Tasman Sea high pressure systems while developing deeper than
normal trough systems over inland and tropical Australia (see Figure 2). This, in turn, produces more
persistent onshore winds along the NSW coastline from the Illawarra region northwards, bringing
with it increased rainfall. With the large scale winds from the pressure systems being onshore the
sea breeze effects are reduced. For the very strong north easterly sea breezes of old there needs to
be hot conditions inland with a slight offshore breeze in the morning, ideally from the north west, to
enable an enhanced sea breeze to develop. But with increased persistence of the onshore winds this
pattern has not been able to develop.
So, as is often the case, what is happening in our oceans determines the weather we experience on
the land.
Figure 1: Sea surface temperature anomaly pattern for January 2012.Source: NOAA/ESRl/PSD.
Figure 2: Mean sea level presuure anomaly pattern for January 2012. Source: NCEP Reanalysis.
Figure 3: 10 metre wind vector (metres/second) anomaly pattern for January 2012. Source: NCEP
Reanalysis. | 
