Not so dry July
Fresh monthly data has come in regarding the synoptic setup across our various swell generating basins, from the Indian Ocean through to the South Pacific, and it paints a pretty clear picture.
I don't plan on doing these analysis articles monthly, but when the data is interesting to look and talk about I'll delve into it.
During June we saw a low pressure anomaly south of the Bight bringing lots of westerly energy with clean conditions for South Australia and Victoria, while a strong high sitting just behind New Zealand provided plenty of fun sized energy out of the east.
Looking at last month, July, Indonesia continued to pump as the same swells that impacted Western Australia travelled north. WA itself generally saw clean conditions north of an imaginary line drawn just below Mandurah, while to the south it was mostly onshore. Victoria's Surf Coast failed to see any significant swell at all though conditions were good to great for the more open beaches.
Tasmania's South Arm remained small to tiny for most of the month, while the East Coast saw plenty of activity owing to the clustering of low pressure systems through the Tasman Sea. These same lows generated significant back to back swell events for southern NSW, with less size but great waves further north and into Queensland.
Having a quick glance at the Mean Sea Level Pressure anomaly charts (difference from the climate average) we can see a strong and broad low in the Indian Ocean, a north-west to south-east aligned high across southern Australia and then a dip through the Tasman Sea.
The reason for the strong anomaly in the Indian Ocean is due to the polar jet being driven north just ahead of (read east of) the MJO, which has been near stationary between 60-100E and off eastern Africa.
This has brought the endless run of swells for Indonesia and Western Australia, while the positioning of the high has directed winds more from the northern quadrant across that state.
What is also apparent is the blocking influence of the high pressure anomaly across the southern states, leading to the run of poor waves on the Surf Coast but out of season and fun surf across the more exposed breaks. South Australia has seen similar favourable conditions with smaller swells.
Not much has to be said about the East Coast. Southern NSW has had one of the better winters in the last decade with the supporting ridge of high pressure from Tasmania to New Zealand, cradling lows as they developed in the Tasman Sea.
When looking at the mean (not anomaly) jet stream, that being the winds through the upper atmosphere at around 500mb, we can see that there is a split across eastern Australia and the Tasman Sea. This occurs when the jet stream encounters a blocking pattern, and this can be seen at the surface in the anomaly across central and southern Australia in the image above.
With a split in the jet stream like that shown, multiple storms can form in the same spot due to the almost static air aloft. Sound familiar? This is one of the reasons behind the clustering of lows and storms off the East Coast.
Looking ahead and the European Centre for Medium Range Forecasting (ECMWF) has higher than normal pressure forecast under Australia and across to New Zealand through August, with a low pressure dip off the NSW coast, slowly weakening into September though still there. This would likely result in a continuation of average conditions for the Victorian Surf Coast and plenty more swell for the the East Coast.
We'll continue to monitor what is shaping up to be quite a year of weather watching.