After a slow tropical season in 2014, how are things looking for the 2015 Atlantic hurricane season? Interestingly, we did get off to a very early start. While it did not have much of an impact on the Northeast, Tropical Storm Ana was able to develop off the coast of the Carolinas. However, despite the anomalous early season storm, 2015 is anticipated to be another year of suppressed activity in the Atlantic Ocean. Let’s take a look at some of the factors expected to influence tropical activity during this upcoming hurricane season.
After being in a predominately positive phase this past winter, the North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) are expected to have important implications for tropical development during the summer and fall. A positive NAO/AO pattern is characterized by a stronger than usual subtropical high in the central and eastern Atlantic. As a result, easterly winds (trade winds) across the Atlantic are generally faster than average. This in turn will promote higher than normal wind shear, an enemy of developing tropical cyclones. Also, strong trade winds are also associated with increased upwelling off the West Coast of Africa. This allows colder, deep ocean water to mix upward towards the surface, thus favoring cooler than normal sea surface temperatures (SSTs) in the region. Since warm ocean temperatures are vital for tropical development, the below normal SSTs are likely to impede overall activity.
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One of the major themes in the world of tropical weather since the spring of 2014 has been the state of El Niño. While accurately forecasting El Niño has proved to be quite difficult over the last year, El Niño conditions finally emerged during March 2015. El Niño is significant, as it is generally correlates to higher amounts of wind shear and lower tropical activity across the Atlantic Basin. El Niño conditions are currently expected to continue for most, if not all, of the upcoming season. This also provides confidence to a forecast of decreased hurricane activity in 2015.
After taking into account the state of NAO/AO and the thriving El Niño, it should not come as too much of a surprise that we are predicting a relatively quiet season. Above is a table that shows the number of tropical systems we expect for the 2015 Atlantic hurricane season. Despite already having one in the books, only 6 – 10 storms are predicted overall. Of these named storms, 3 – 5 are anticipated to develop into hurricanes, with 1 – 2 reaching major hurricane status (Category 3 or higher, winds of 111+ mph). These values all fall below the climatological values of 11 storms, 6 hurricanes and 2 major hurricanes.
With below normal activity expected in the Atlantic, there will likely be fewer opportunities for a direct strike from a tropical system in 2015. In addition, meteorological records show that during El Niño years, tropical cyclones are generally favored to strike the Gulf and Southeast Coast. Nevertheless, it is important to always stay vigilant, as it only takes one storm during an otherwise slow season to inflict damage across our area.
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