How did last week's XXL Nazare session compare to previous ones in November 2017, aka, Rodrigo Koxa's record setting day and January 2018, an all-time XXL session. Let's take a look at where the swells came from and what their main differences were once they arrived at Nazaré.
All three swells were large and long-period, and were generated by broad areas of strong westerly winds in the northern half of the North Atlantic. These windfields were all brought about due to atmospheric pressure difference between a depression in the north and an anticyclone in the south.
Live cam: Nazare
But there were some interesting differences. For example, the low pressure to the north had different origins in all three cases; the open-ocean wave heights in the centre of the storm, and the direction from which the swell arrived at Nazaré weren’t the same each time.
Related content: Gallery and Vids from XXL Nazare Last Week
The 2017 swell originated from a low that appeared off the coast of northeast Canada, tracked across to Cape Farewell and deepened very quickly. It then continued moving to a position just south of Iceland, as a high developed just north of the Azores at the same time. It was the pressure gradient between these two systems that led to a moving area of gale-force winds west of Ireland, which, in turn, generated a big swell as it tracked eastwards. The tangential swell that emerged to the south of that fetch eventually reached Portugal.
The origins of the 2018 swell can be traced back to two features: a large, stable area of high pressure over the Azores and a low that appeared off the east coast of Greenland and then spread across the far north of the North Atlantic. This resulted in a massive area of westerly winds covering the entire northern half of the North Atlantic, which persisted for about 48 hours. Again, the tangential swell that pushed south from that fetch was what caused the large waves at Nazaré.
The main factor responsible for the 2020 swell was an ex-hurricane called Epsilon. Epsilon had been active for several days in the western Atlantic, and had passed Bermuda as a powerful hurricane, before moving north into cooler sea-surface temperatures. If it hadn’t been for a lucky upper airstream configuration and a low that developed in the Labrador Sea, Epsilon might have weakened and faded away. As it happened, the energy of the two systems merged together, and exploded into a huge low pressure in the mid North Atlantic, with near hurricane force westerly winds on its southern flank. This generated humungous wave heights west of Ireland and a gigantic, very long period swell that spread down to the rest of Europe’s west coast, including Nazaré.
In 2017, the open-ocean wave heights and the swell sizes at most spots were not over-remarkable. Obviously most north, northwest and west-facing spots got some largish, long-period swell, but nothing really exceptional for a North Atlantic winter. Wave heights along the Portuguese coast were around 12 to 15 feet, for example. However, the breaking wave heights at Nazaré were much, much bigger than everywhere else. The direction of the swell was probably an important factor in this case: the slightly more northerly direction hitting the canyon at exactly the right angle. The A-frames that resulted at Praia Norte were almost triple the height of the raw swell.
The 2018 swell hit the Portuguese coast with considerably bigger wave heights (between about 15 and 20 feet) and longer periods than the 2017 swell. The swell direction was very slightly more west, but hardly significant. All in all, the size of the waves at Nazaré would have been bigger than in 2017, but maybe not so much bigger in proportion to the open-ocean heights. The mechanism at Nazaré that refracts and combines the incoming swells is highly sensitive, and, sometimes, the multiplication factor might not necessarily increase with increasing incoming wave heights.
The 2020 swell filtered down into Portugal with open-ocean wave heights smaller than most places further north, but with periods exceeding 20 secs. The direction was, on average, about ten degrees further west than the 2017 swell, with open-ocean wave heights exceeding 15 feet. In this case, even though the breaking wave heights at Nazaré were truly humungous, the magnifying effect might not have been at its optimum.
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Finally, one big difference between the 2020 swell and the other two was the local wind conditions. In 2017 and 2018, there were moderate to fresh northerlies – typical in Portugal. In 2020, however, a cell of high pressure pushed in from the west at the same time as the swell arrived, making conditions clean, with light variable winds or light easterlies.
As for how big it was last week, the size is comparable to 2018 -- but until officials get the yard stick out and begin measuring, we won't know specific heights. One reader did send through this image of Sebtastian Steudtner's wave though? 120 feet, may be a bit pushing it.
Cover shot of Sebastian by Helio Antonio