An autumnal April
We're over halfway through autumn, but this one's different. Having to stay home and surf locally removed the opportunity to chase surf, but it also allowed surfers to get more in synch with their local. In fact, you had to time the tides and tweaks in swell directions to beat the significant increase in crowds.
But the past month has had a much more 'autumnesque' feel compared to recent years where summer seems to drag on deep into April and May.
The reason for this, especially across the south-eastern part of the country was a strong negative Mean Sea Level Pressure anomaly for the month of April (purple blob below). This means that we saw much lower pressure than normal (compared to historical data from 1981-2010) spreading from South Australia over to New South Wales, including Victoria and Tasmania.
The difference from normal was quite significant as well, down to near 10hPa below the climate average, and the flow on effects for not just the southern states but the East Coast were very noticeable.
The cause of the anomaly was a strong and persistent negative Southern Annular Mode (SAM) through all of April, lifting the westerly storm track closer to Australia.
With such a large low pressure anomaly, the resultant wind anomalies were westerly through the Bight and across Victoria, bringing plenty of westerly swell, though also with plenty of wind.
The main beneficiaries from this pattern were South Australia and Victoria. The Adelaide Mid Coast offered fairly consistent surf all month from the persistent fronts pushing up and across Western Australia, though it was to the detriment of the rest of that state (especially through the second half of April).
Victor Harbor enjoyed the winds from the north-western quadrant, while the Surf Coast in Victoria received a steady flow of westerly swells with favourable conditions under zonal westerly breezes. While not especially large, there's been plenty of fun days to pick and choose from.
Tasmania saw swells from west to south and a few point days with much cooler weather than normal, 1.45 degrees below average.
With all this cold windy and wet weather it's no surprise that Tasmania saw its wettest April since 1960, Victoria since 1974 and its third wettest on record. In contrast though Western Australia saw its second hottest April on record linked to interior heat built up with the lack of cloud from the (non-existant) monsoon this summer.
We can clearly see this in the rainfall and temperature charts, and the end result for the nation, even with a cooler south-east of the country was the 42nd consecutive month of warmer than average national temperature, with April being the 5th warmest on record.
The flow on effects for the East Coast has been a switch from the normal easterly trade-swell regime for SE Qld and Northern NSW to diffracted southerly groundswell energy from the Southern Ocean and Tasman Sea. While it's kept most locations busy with swell, we're now staring at another below average autumn of surf for the East Coast unless things change in the coming few weeks, and this looks unlikely.
The north-west wind anomalies through the Tasman Sea tell the story (second image above).
One positive development through April was the build up of heat in the seas off North West Australia, feeding moisture into north-west cloud bands which traverse across the interior of the country and are bringing much needed rain to the more inland regions of the country.
This is set to continue through winter and the models that try and forecast the Indian Ocean Dipole are now favouring a strong negative event. This is opposite to last years strong positive event and will see a wetter winter across the south-east of the country though with the extra cloud cover, warmer morning minimum temperatures.
We'll continue to follow these events as they unfold over the coming months.