30 June 2014
An El Nino is probably on the way for this autumn and winter, but despite what you may have heard about floods and fires, it’s not looking (right now) as if it will be a strong one. The strength of the El Nino IS a big deal however, because weak to moderate El Nino episodes tend to have different and milder impacts on worldwide weather, than the super strong ones like the one in 1998. Forecasting how strong they will get is not something we have a lot of skill at either, so there are some significant uncertainties, and that’s something you should remember if you read a story online, or see something on network news about it. (If you see something on the History channel about it, just change the channel and go back to the program about aliens building the pyramids with the help of the Nazis.)
Let me show you some examples from past warm episodes. Below are some rainfall anomalies from Climate.gov for strong El Nino episodes:
Now, look at what happens in moderate and weak episodes:
What do you notice??
Well, if you are in Illinois to Ohio, you should notice that it seems to be dry not matter what kind of El Nino we see, but just about everywhere else you see a LOT of variance. The message here is a big one: Mother Nature rarely provides a magic bullet you can hang your hat on. The public tends to affix the blame for acts of nature and economic collapses on one cause, but in the real world it’s rarely that straight forward. (Climate change skeptics like to say it’s the sun causing the warming, but when you show them the sun is actually gotten a tiny bit less bright over the past 20 years, they switch to cosmic rays etc.)
The current forecast for this El Nino is for temps to approach 1 degree C above normal in the Nino 3.4 region of the Pacific. This area (by mutual agreement) is where an El Nino’s strength is determined. To be a full-fledged El nino, the temp is this region needs to be 0.5C above normal for 5 consecutive 3 month seasons. It’s just now reached the 0.5C level, so it has a way to go!
I was talking with some of the scientists who specialize in El Nino at the AMS Weather conference last week and they pointed out that while the water temperatures are looking like El Nino, the atmospheric flow pattern has not yet followed suit. Until it does, the affects will be very negligible, and the only real summer impact of El Nino is a strong reduction in tropical cyclone activity in the Atlantic Basin. Keep in mind though that it only takes one land-falling storm to cause catastrophe and one storm that illustrates this is Hurricane Andrew in 1992. That was an El Nino year hurricane.
So, every El Nino is different and there are even two different types of El Nino’s, but I’ll save that for another post!