What has been suspected for quite some time was officially proclaimed today by the Climate Prediction Center: El Nino is alive and well. The warming of the waters in the equatorial Pacific Ocean directly impacts weather across the globe, and the forecast for spring represents what we would expect during an El Nino year. Here in the Southeast we can expect above normal rainfall along with temperatures that could go either way. Chances are it will turn out cooler than normal.
So what exactly is El Nino? As stated above it is a warming of the waters along the equatorial Pacific.
The warmer sea surface temperatures have an effect on the upper level winds that form over the Pacific Ocean, and eventually cross the United States. What typically happens is a split in the jet stream develops along the West Coast with a large ridge of high pressure developing across the west in the northern branch of the jet. The southern branch of the jet stream dives across Mexico and the Southwest transporting Pacific moisture into Texas, and eventually collecting Gulf of Mexico moisture that makes it here to the Southeast. With that in mind we usually expect to see wetter conditions which is what is expected this spring. Along with the wet weather, slightly cooler temperatures can be expected as well. This typically keeps the number of severe weather events lower than in a non-El Nino year. This doesn’t mean that severe weather won’t happen, it simply means that the number of severe weather events should be less.
With a stronger and more active southern branch of the jet stream present we can also expect a quieter than normal tropical season. Stronger than normal winds in the upper levels of the atmosphere crossing the tropics from west to east are counter productive to the development of tropical systems.
The last time we had an El Nino during the tropical season was the summer of 2009. That summer we wound up with the average number of named storms (10), but only had 3 hurricanes compared to the average of 6, and came out with 2 major hurricanes compared the average of 3. None of the hurricanes hit the United States. Just like with tornadoes this in no way implies that a catastrophic hurricane will not impact the US. In fact one the costliest hurricanes ever, Andrew occurred during the El Nino summer of 1992. Stay tuned.