La Nina Fading In Eastern Pacific Making Seasonal Forecasts Even Tougher

Good afternoon again. I was reading the newspaper this morning, and noticed an article on the neutral global climate pattern, and how it could make seasonal forecasts for Atlantic hurricanes even tougher.

NOAA issued its seasonal forecast a couple weeks ago, and indicated another above average season with 12 to 18 named storms, 6 to 10 hurricanes, and 3 to 6 major hurricanes. Colorado State University as well as WSI also issued forecasts back in April with CSU’s updated forecast to come out later this month.

Over the past couple months, the La Nina pattern, which has been blamed for the blizzards and snowstorms in the Northeast and the severe weather in the South and Midwest this year is beginning to erode, and we are falling into a more neutral global pattern according to an article by Tamara Lush of the Associated Press.

The article also indicated that the neutral pattern is affecting how forecasters have been putting together their seasonal forecasts. It is much easier to forecast when you know either a La Nina or El Nino is in control. For those not familiar, La Nina is the climate condition when cooler than normal sea surface temperatures exist in the Eastern Pacific while El Nino is when warm than normal sea surface temperatures exist.

The current La Nina pattern was responsible for a very active tropical season in 2010. There were a total of 19 named storms, 12 hurricanes, and 5 major hurricanes. Other active seasons that had strong La Nina signals were 1995 and 1998. However, in 2005, there was a neutral signal, and that season turned out to be the most active on record in addition to being the most devastating and one of the most deadliest in years.

There are other factors that determine an Atlantic Hurricane Season forecast including: Rainfall in the Sahel region of Africa, sea surface temperatures in the Atlantic, moisture levels in the Atlantic, and barometric pressures in the basin as well. When you have a La Nina pattern though, conditions for tropical development become enhanced since there are not as many storms in the Eastern Pacific to stir up upper level winds in the Atlantic. Conversely is the case when you have an El Nino pattern.

One thing that is important though, and that is just because you either have or don’t have certain ingredients for an active season, it doesn’t necessarily mean that a location along the Eastern Seaboard of the United States will not be impacted by a major hurricane. Hurricane Andrew proved that to us in 1992.