James Waller, PhD, Research Meteorologist
Seasonal outlook providers continue to issue early predictions for the 2018 North Atlantic hurricane season. The Weather Company (IBM) is expecting a season of near-normal activity. Earlier this month, the Tropical Meteorology Project at Colorado State University (CSU), predicted a season more in line with the 1995-2017 elevated average. Meanwhile, North Carolina State University (NCSU) issued a prediction for above-normal activity, relative to the 1995-2017 average.
The variation in predictions reflects some uncertainty with the factors involved. Key factors for 2018 include an expected neutral state of the El Niño Southern Oscillation (ENSO), and variable sea-surface temperatures (SSTs) in the Atlantic Basin. The need for proper preparation, as with any hurricane season, is noted by these providers.
ENSO
This describes shifting SSTs in the Tropical East Pacific. The warm phase or "El Niño" is related to elevated wind shear in the Tropical Atlantic Basin. This elevated wind shear disrupts tropical cyclone formation, usually with a reduction in hurricane counts for the Atlantic Basin. The cool phase or "La Niña" is related to elevated hurricane counts in the Atlantic Basin due to reduced wind shear.
La Niña conditions are still present since their onset last fall, according to the NOAA Climate Prediction Center (CPC). Conditions are expected by the CPC to transition to neutral over the coming months, and remain in a neutral state through the peak of hurricane season from August to October. All else being equal, this would be associated with normal hurricane activity in the Atlantic basin. The onset of a weak El Niño is possible, but it is unlikely that this would significantly influence wind shear or hurricane frequency.
Both model and statistical forecast guidance show considerable uncertainty, however confidence should improve toward the end of spring.