Colorado State University Calling for Below-Average Atlantic Hurricane Season

Colorado State University (CSU) issued its final update to their Atlantic seasonal hurricane forecast today, August 2, and call for a below-average remainder of the hurricane season. Their final forecast is for a total of 12 named storms (including the three named storms that have already formed), 5 hurricanes and 1 major hurricane (winds >= 111 mph; Category 3+ on the Saffir-Simpson Wind Scale). The average hurricane season has 12 named storms, 6 hurricanes and 3 major hurricanes. While the 2018 season got off to a relatively quick start with three named storms forming by the middle of July (Alberto, Beryl and Chris), the CSU forecast team anticipate that the rest of the season should be quieter than normal.

One of the primary reasons for the prediction of a below-average season is that the tropical Atlantic is currently much colder than normal. Hurricanes thrive on warm ocean water, so cooler waters provide less fuel for hurricanes to develop and intensify (Figure 1). The tropical Atlantic atmosphere is also much drier than normal, suppressing the formation of deep thunderstorms that are the building blocks of hurricanes. Over the past several weeks, the Caribbean and central tropical Atlantic have also been experiencing much stronger vertical wind shear than normal (the change in wind direction with height in the atmosphere). These stronger than normal winds tear apart developing tropical cyclones as they are trying to form.

The tropical eastern and central Pacific is slightly warmer than normal at present, and there is some potential that these waters might continue to warm and reach El Niño levels during the next few months. If this were to occur, it would also tend to enhance Atlantic vertical wind shear, further promoting unfavorable conditions for Atlantic hurricanes.

While the Atlantic seasonal hurricane forecast from CSU and most other groups (see http://www.seasonalhurricanepredictions.org for predictions from over 20 submitting forecast entities) now calls for a below-average season, it is important to remember that significant hurricane landfalls can occur in otherwise quiet seasons. Two recent examples of this are Hurricane Alicia in 1983 and Hurricane Andrew in 1992. It only takes one hurricane landfall near you to make it an active season. 

2018 Hurricane Sea Temperatures
Figure 1: July 2018 sea surface temperature anomalies.

About the Author:
Dr. Phil Klotzbach has received national and international attention for his work in researching weather patterns and forecasting hurricanes. He currently is lead author on Colorado State University's Atlantic basin hurricane forecasts which he releases every year with his colleague Dr. Michael Bell.