The main driver of this year’s lower than average outlook is the anticipated development of El Niño this summer. El Niño causes stronger wind shear, which reduces the number and intensity of tropical storms and hurricanes. El Niño can also strengthen the trade winds and increase the atmospheric stability across the tropical Atlantic, making it more difficult for cloud systems coming off of Africa to intensify into tropical storms.

2013 Re-Cap: What Happened?

Despite pre-season predictions of an active tropical storm season for 2013, the actual tropical storm/hurricane activity for that year was much lower than originally forecast.

The 2013 actual activity compared with the pre-season forecast was

In addition, the 2013 Atlantic hurricane season ended with something that hasn't happened in 45 years. No hurricanes were rated Category 2 or greater in the Atlantic, Caribbean or Gulf of Mexico, the first year without a Category 2 or stronger hurricane in the Atlantic basin since 1968.

The season's lone two hurricanes, Humberto and Ingrid, only reached Category 1 strength.

The factors favoring lots of storm activity typically include low surface pressures, warm sea surface temperatures, a strong African easterly jet (which enhances disturbances that enter the Atlantic and can potentially grow into storms), and the lack of an El Niño (which can promote hostile westerly winds).

A lot of analysis has been undertaken to understand why 2013 activity was so far below the predicted expected level.

Numerous factors which hindered 2013 tropical storm activity were involved but one primary element that was in effect across the heart of the tropical Atlantic was very dry air. While some previous active seasons have had drier-than-normal air present, it had not reached the extreme seen in 2013.

Colder than normal ocean surface temperature in an area west of Portugal was another suppressing factor that wasn’t generally accounted for.

In summary, actual conditions which evolve during the tropical storm season in the Atlantic basin can often play havoc with pre-season predictions.

Looking at Recent Year Forecasts Vs Actual Storm Activity

Below is a table originally published by Stan Blazyk in his Galveston County Daily News Weather Blog on April 13, 2013 (which we have now updated to include 2013 actual results) that shows the April pre-season forecasts over the past several years with the actual number of storms for each year.

Predictions Are Only Partially of Interest

While predictions for the upcoming season are interesting and may give an indication of the overall expected activity, the averages don’t matter much when a storm is threatening the area in which you live.  

So, as usual, all interests near or along the U.S. Atlantic or Gulf of Mexico coasts should be alert to developing tropical storm activity and should make early preparations if forecasts indicate that any storm may head in your direction.