In the last few weeks, we’ve nearly kicked the drought conditions across much of the state with abnormally wet weather. The El Nino phenomenon has global effects, and of course impacts the weather here in the Brazos Valley. While the dynamics of El Nino are complicated, simple predictions can be made about the weather.
But first, just what is an El Nino? An El Nino is a shift in the sea surface temperatures in the largest of Earth’s oceans: the Pacific Ocean in its waters near the Equator. The Atlantic and Indian Oceans are too small to support such a large-scale event like an El Nino. Beneath the surface, water is transported not only horizontally, but vertically as well. Cold ocean water from deep in the ocean moves upward once it bumps into the continent of South America. This process is called upwelling.
In a normal year, the sea surface temperatures of the western Pacific are much warmer than in the eastern Pacific (about a 14 degree difference). In an El Nino year, we see this pattern switch.
The trade winds which blow from the east near the equator calm. As a result, we see less upwelling and the waters in the eastern Pacific warm up. In addition to the temperatures changing, the rain changes as well. The typically wet western Pacific becomes much drier, and more rain is seen in the east. This switch causes global changes in atmospheric circulation that affect weather across the globe.
This cycle usually re-emerges every two to seven years. In between El Nino years we may see normal conditions or we can have a La Nina, where the eastern Pacific becomes abnormally cold near the equator.
What does that mean for the Brazos Valley? Not much in the summer, but effects clearly show up in wintertime. First, as you might have suspected, we generally see much wetter weather. There is not a huge effect on our temperatures, but things do tend to be a little cooler in Southeast Texas. Possibly the best effect of El Nino years for us is the decrease in the number of hurricanes that form in the Atlantic. You’re probably aware that the 2009 Atlantic hurricane season has been relatively uneventful, and after Ike last year, there probably couldn’t be a better time for some quiet in the Gulf.