As we continue to enjoy this winter season, the last thing in the world we want to think about is the upcoming hurricane season.
As we approach spring, most of us in the meteorological community start preparing for the upcoming tropical season by attending conferences and studying tell-tale signs that give us an idea of how the atmosphere is setting up.
Please keep in mind that there are many variables that factor into hurricane activity. The ocean is one of them and usually of most interest to weather geeks.
One of the primary indicators we look at is the sea surface temperature. We’re not as interested in the current temperature as we are in the temperature anomalies of the ocean.
An anomaly is a "departure from normal." In other words, is the temperature of the ocean warmer than normal? Is it colder than normal? Or is it just right where it should be?
The ocean, like the atmosphere, develops a natural rhythm and cycle. However, the atmosphere responds to what the ocean is doing. It is the primary driving force of the atmosphere and any changes to normal ocean patterns will affect how the atmosphere behaves.
Decades of research have led many climate predictors to focus in on one particular region of the world's oceans. The equatorial water of the Pacific Ocean off the coast of Peru and Ecuador is ground zero for the phenomenon known as El Nino and La Nina.
When an El Nino occurs, westerly winds in the atmosphere push warmer-than-normal water from the western Pacific into the eastern Pacific off the coast of South America.
For the purpose of describing how it affects our hurricane season, just know that those westerly winds will usually extend into the Atlantic Basin. Think for a moment, what direction do hurricanes usually come from? They usually come from the east.
So, during an El Nino year, tropical cyclones will encounter these winds from the west. This creates an environment of "wind shear." The winds from the opposite direction will have a tendency of tearing the tops off of tropical systems before they really have a chance to develop.
When a La Nina occurs, the result is the opposite of an El Nino. Persistent easterly winds in the atmosphere push the warm water away from the coast of South America, causing that warmer water to be replaced by colder than normal water near Ecuador and Peru through a process we call upwelling. That is the marker that tells us a La Nina has formed. Those easterly winds are usually found in the Atlantic Basin.
So, when a tropical cyclone moves in from the east, there is no wind to shear or tear the storms apart. Often times, the winds that form La Nina will aid in a storms development in the Atlantic.
El Nino usually equals a quieter than normal hurricane season.
La Nina usually equals a busier than normal hurricane season.
The experts at NOAA and the Climate Prediction Center say that we are currently in a "neutral phase." However, the forecast models are leaning toward an El Nino forming sometime in the spring.
Even though that may trend toward a quieter than normal season, we still have to be mindful that not all tropical cyclones come from the east.
Many storms can form in our own back yard. Plus, all it takes is one storm to ruin your picnic. We'll keep you posted on the development of this upcoming El Nino.