From the Cliff Mass Weather Blog
Cliff Mass
We are now at the height of a very warm El Nino and some folks are worried.
Some worry about lack of precipitation and snowpack.
But as I have noted in a previous blog, the very strongest El Niños generally bring near-normal precipitation and mountain snows to our region.
Others worry about Northwest coastal flooding due to Kelvin waves moving up the coast from Southern California (see sample below).
The truth is that El Nino and accompanying coastal Kelvin waves shouldn’t pose a serious flooding threat to our coast.
In an earlier blog, I described Kelvin waves and how they weaken when they move north up the West Coast. Stronger over southern CA, but greatly weakened up our way.
But there is another reason you should not lose sleep about coastal flooding:
Another mode of natural ocean variability, the Pacific Decadal Oscillation (PDO), will be fighting it.
Let me explain.
El Nino produces a certain warm-water pattern as shown below (from yesterday), with warmer than normal water over the tropical Pacific and along the southwest US and Mexican coasts. Our sea surface temperatures (SST) are far closer to normal in such years.
El Nino strengthens and weakens (into La Niña) over a period of roughly 5-7 years.
The Pacific Decadal Oscillation produces a similar temperature pattern to El Nino during its warm phase (see below).
But here is the key point.
The PDO varies on a time scale of many decades and is currently in its COLD phase, and thus is OPPOSING the warm El Niño. It is also relatively strong on our coast.
As shown below, we have mainly been in a cold phase during the past several years.
The PDO cold phase tends to bring below-normal water levels to our coast. Since the PDO is generally weaker than El Nino, that means it tends to reduce the El Nino signal in temperature and sea level rather than eliminate it.
Sea surface temperatures are not quite as warm. Sea level is not as high.
You can see this by looking at sea level at La Push on the Washington Coast from October 1 to today. (below). Normal conditions are shown by the light blue; red is this year.
During the past month, sea level has been slightly higher than normal. A modest addition, but nothing serious.
Minor flooding is shown by the brown band. We never reach it. No worries.
Want more proof that PDO is our friend?
Here is the long-term trend of sea level at Toke Point on the Washington Coast (below).
You will note that there is essentially no long-term trend.
The highest sea level years were during two strong El Niño years (1983, 1998), indicated by the red arrows. But the latest strong El Nino year (2024-25) was not exceptional because the PDO was quite negative.
We will enjoy PDO “protection” this year as well, so predictions of El Nino flooding on the WA coast by certain local media outlets and some social media channels are exaggerated.
