August SST anomalies in the tropical Pacific
Earlier in the year, it seemed almost a certainty that El Niño would develop in the tropical Pacific. As we moved through the spring and summer, the tropical Pacific began to warm and it looked like we were well on our way to seeing an El Niño develop. Then, it just stopped.
In recent weeks, the tropical Pacific has actually cooled significantly, especially in the
October SST anomalies in the tropical Pacific. Notice the cooling along the Equator
central Pacific. Just compare the two SST anomaly maps from August and now. You can clearly see a substantial decrease in SST anomalies across the tropical Pacific.
So what happened? It’s hard to say. The latest report from Australia’s Bureau of Meteorology site addresses the retreat in SST values across the region that was warming up until recent weeks. It seems that the pressure pattern across the Pacific changed and the abnormally weak trade winds picked up, cooling the sea surface rather quickly.
Sub-surface temperatures in the tropical Pacific. Notice the distinct cooling in recent weeks
It is also very interesting to note that the sub-surface temperatures also have declined in dramatic fashion since the late summer. While there was a growing pool of warm water since the spring, it suddenly cooled and now we have a noticeable large area of cooler than normal sub-surface water across a large section of the Pacific. This means that the chances of seeing a true El Niño are getting quite slim.
Why is El Niño even an issue? Well, aside from the weather patterns that El Niño tends to have an influence on globally, if we look at the Atlantic hurricane season specifically, there tends to be a suppression of overall activity. This is mainly due to the increase in tropical convection over the Pacific which is due to the increase in sea surface temperatures because of the El Niño. Persistent tropical convection over the Pacific will usually mean stronger upper level winds and sinking air across the tropical Atlantic. These two negative factors limit the amount of development typically seen in the Atlantic main development region. It’s interesting that the end result seems to have been present this season. In other words, we have seen a limit to the numbers of hurricanes that have developed in the deep tropics. In fact, the ONLY major hurricane to form did so well outside of the typical breeding grounds and was very short-lived.
I do not understand why we had the effects of El Niño without the El Niño itself. Perhaps the atmosphere was responding as if there was an El Niño coming on even though the tropical Pacific was not quite there yet. Who knows? It’s all so complex and there are many interactions between the ocean and atmosphere that it’s difficult at best to know the real reasons behind some of this.
The bottom line is that El Niño has been put on hold, or so it would seem. It may be that it never fully takes root and this could have an effect on the upcoming winter season and most certainly the 2013 Atlantic hurricane season. None of the reliable climate models indicate an El Niño for the early part of 2013 and one could reasonably assume that there won’t be an El Niño during the peak of next year’s season in August-September-October. And yet, even with the near-El Niño observed this season, the Atlantic still has managed to produce eight hurricanes total. This is above the 100 year average. And, on the topic of abnormal sea surface temps, the tropical Atlantic was thought to have been cooler than normal this season. It wasn’t and still isn’t. In fact, a good deal of the tropical Atlantic is running nearly 1 degree C above normal right now. I guess there is a lot we still do not understand about our oceans and the atmosphere.
I’ll have another post here later this afternoon to address the current goings on in the tropics and what we might expect with 98L.