I talked about the developing El Nino in a post last month (Developing El Nino), and it’s officially here (El Nino Arrives; Expected to Persist through Winter 2009-2010). While that might be nice to know, what’s more important is what effect it will have on the weather–from now through the upcoming winter.
The El Nino is weak now, but what is most interesting in the above-linked NOAA release is that they “expect it to continue developing during the next several months, with further strengthening possible.” The key to its effect on the weather–across the United States and the entire globe–is related to how much it strengthens.
If the El Nino remains weak, its impact on the weather will be minimal–although the El Nino might be blamed on everything under the meteorological sun. Since the NOAA release has left the door open for the possibility of a stronger El Nino, I will briefly talk about some of the effects of a stronger El Nino.
Atlantic Hurricane Season
When an El Nino develops during the summer, it can reduce the number of hurricanes in the Atlantic Basin. In fact, the belief that an El Nino would form is part of the reason that many hurricane forecasts for 2009 were for a relatively low number of named storms. While that’s certainly potentially good news, the number of hurricanes is not terribly important—what’s important is the number of tropical storms and hurricanes that make landfall, and the strength of those individual storms.
El Nino and Winter Weather
The effects of a strong El Nino are more significantly felt during the winter in the northern hemisphere, and I’ll talk about the effects on U.S. weather briefly today—-with more detail later if warranted.
More Active Southern Storm Track
Having one storm track in the winter is rare; there are usually at least two. During an El Nino, the southern storm track is more active, with more and more potent storms, because of the extra energy added by the warm water of the equatorial Pacific. This typically results in more than than average in the the Desert Southwest (some El Nino years result in serious flooding in Southern California, for instance) and normal or below normal rainfall in the Pacific Northwest. More rainfall that normal typically occurs in the Southeast.
The strength of the southern jet also means that mild, Pacific air often invades the United States, keeping typical winter cold at bay, especially in the northern Plains and northern Rockies.
The result of an El Nino is often less winter weather–although as it weakens, there is the potential for significant snowstorms in the Northeast during the latter part of winter.
Again, I’ll have more details about the possible effects of El Nino as the expected strength and duration becomes more clear.
NOTE: For a preview of the winter forecast, see Snowy, Cold Winter on the Way?
–Paul Yeager
