The coming Atlantic hurricane season is shaping up as a battle between oceans. The Atlantic and Pacific Oceans are sending conflicting signals about how active Summer, 2014 will be in the Atlantic basin.
As global air temperatures rise, ocean temperatures also rise. Currently most of the Caribbean, the Gulf of Mexico, and the tropical Atlantic, shows a positive temperature anomaly.
High sea surface temperatures are correlated with above-normal tropical cyclone activity. But in the Pacific Ocean, an El Niño, a warming of the water off the coast of South America, is developing; El Niño is correlated with below-normal activity in the tropical Atlantic.
Hurricanes feed on the latent heat bound up in water vapor molecules. Energy is required to rip these molecules from the ocean, and this energy resides in the water vapor until it condenses, at which point the energy is released as sensible heat. When conditions are favorable, tropical storm systems turn the sensible heat energy into kinetic energy — energy of motion — commonly known as wind.
An influx of sensible heat in the atmosphere, such as occurs when a large amount of water vapor condenses, induces the air to rise, and when the rising air couples with an easterly wave that closes into a low pressure system, a tropical depression is born. If favorable conditions persist, the depression becomes a tropical storm, and ultimately a hurricane.
A Factor That Inhibits Hurricane Formation Even When Water Temperatures Are High
Latent heat’s potential conversion to wind can go untapped if the second requirement for tropical storm formation is not present: relatively low vertical wind shear (a change in the direction or speed of the wind with height). A change of wind with height disrupts a developing tropical storm’s vertical structure and the storm cannot form properly. When the winds are the same at all levels in the atmosphere, a tropical cyclone can rapidly intensify.
El Niño And Its Effects, Locally And Globally
An El Niño is a major warming of the eastern Pacific equatorial waters (as much as ten degrees Fahrenheit). El Niño was first noted for its effect on the anchovy fishery off Peru: anchovies like cold water and when the water warms, they disappear. It is now known that El Niño has wider-ranging effects than just those on local fisheries.
These include increased fire danger in Indonesia and Australia, and rainier-than-normal monsoons in India and Bangladesh. Closer to home, El Niño causes rain in California and mild winters across the United States.
The El Niño is also correlated with muted tropical activity in the Atlantic Ocean. The rising current caused by the warm Pacific water produces a mid-level jet stream which moves eastward across South America and into the Gulf of Mexico, continuing across the Caribbean and the open Atlantic. During a pronounced El Niño, this flow interrupts the formation of tropical storms by producing vertical wind shear.
Who Will Win The Tug Of War?
The waters across the tropical Pacific Ocean have been warming for several months, and they are now above average in all parts of the equatorial Pacific. Though NOAA’s Climate Prediction Center still considers the El Niño condition to be neutral, it has raised its probability of an El Niño this summer to 65%, and an El Niño watch is in effect.
Here at Decoded Science, we think it’s time to fish for anchovies or cut them up for bait. The pressure pattern (the Southern Oscillation) associated with El Niño — basically enhanced westerly winds in the tropical Pacific — is now in place. Sea surface temperatures are above normal all the way across the equatorial Pacific, recently reaching the coast of South America. And there is a pool of even warmer water below the surface.
For these reasons, Decoded Science is predicting that there WILL be an El Niño this summer.
The Correlation Of El Niño With A Weak Hurricane Season Is Not Precise
The correlation between El Niño and Atlantic hurricanes has been conclusively demonstrated. The overall average number of Atlantic hurricanes per year is six; in an El Niño year the average is four. However, there are abnormal years when an El Niño is accompanied by above average hurricane activity in the Atlantic. 2004, for example, was an El Niño year and four major hurricanes struck Florida.
More important: there WILL be hurricanes this year. Only two years since records have been kept were devoid of any Atlantic hurricanes: 1907 and 1914. The centennial celebration of the last hurricane-free year should not be accompanied by complacency.
Powerful hurricanes can strike in El Niño years and in years of otherwise low tropical activity. Hurricane Andrew, one of the costliest storms in US history, came in an El Niño year with only four hurricanes (1992).
So El Niño or no El Niño, everyone in a hurricane-prone area should be prepared with an evacuation plan in case escape from the fury of a hurricane becomes necessary.