El Nino and Australian swell patterns
Among the international surf community there's been excited chatter about the current El Nino pattern and its prospects for good surf. At present, we're in a strong El Nino and the scientific community is giving it a 90% chance that it will continue into the Northern Hemisphere winter.
Much of the aforementioned excitement is coming from mainland US and Hawaiian surfers because the link between El Nino and swell has been extensively studied there – El Nino seasons are often very good indeed. But what does it mean for the surf in Australia?
Unfortunately there're limited studies on the Australian region, but the little that is known suggests that El Nino doesn't have much influence on our East Coast, especially compared to La Nina when the Coral Sea is much warmer and conducive to cyclone activity.
During El Nino, easterly trade winds traversing the Pacific Ocean weaken (and sometimes even reverse), the result is that warm water 'piles up' in the Eastern Pacific Ocean adjacent to South America.
In the northern hemisphere, El Nino causes the storm track to travel closer to the equator thereby increasing storm and swell activity for Hawaii and California. This shift in storm track further south also results in less swell being aimed into the Pacific North West, ie Washington, Oregon, and the Canadian coast.
During La Nina, however, the trade winds are stronger than normal, warm water piles up in the Western Pacific and Coral Sea increasing the potential for tropical cyclone activity on our side of the ocean. There's also the flow on effects into autumn and winter from warmer than normal water pushing south with the East Australian Current, providing the catalyst for low pressure systems to spawn in the Tasman Sea due to the interaction with cold polar bursts from the south.
Even though the effect of La Nina and El Nino on the Australian wave climate are limited, these diagrams of the Pacific basin reveal an interesting picture. They illustrate the difference in mean significant wave height from the norm when under La Nina conditions (top) and El Nino conditions (bottom).
What's clearly evident during El Nino is an increase in significant wave heights across the North Pacific, as is well documented and observed, but a noticeable drop in wave height across south-western Australia and Indonesia.
Now, besides the large Indian Ocean swell at the end of June, the Indonesian season has been very slow, especially compared to last year's standout season, and that matches the data in the diagram.
Victoria, however, has seen non stop-swell and pumping waves across the Surf Coast, falling in line with the red shading in that region just west of Tasmania.
Tahiti is another region which shows more size through El Nino, and the year thus far has been consistent with numerous large swells hitting Teahupoo.
Looking again at the La Nina diagram, we can see the Western Indian Ocean painted red showing higher than normal significant wave heights, as is the Australian East Coast, while the North Pacific shows a blue hole of lower than average wave heights.
For many years there's been a mistaken assumption that El Nino increases the swell potential everywhere, yet these diagrams show that to be untrue. So keep these diagrams in mind if you're booking a surf trip and want the best chance of swell. First of all check if you'll be travelling during El Nino and La Nina and then choose your destination accordingly. //CRAIG BROKENSHA
Chart: The wind-wave climate of the Pacific Ocean