Forecast: Colorado State University Atlantic Hurricane Season 2017

Aon Benfield

Philip Klotzbach and Michael Bell of Colorado State University (CSU) have issued their June forecast for the 2017 Atlantic Hurricane Season. The forecast calls for 14 named storms, 6 hurricanes and 2 major (Category 3+) hurricanes between the months of June and November. This seasonal forecast includes Tropical Storm Arlene, which developed in the North Atlantic Ocean in April.

With the release of the forecast, Klotzbach and Bell are predicting slightly above average tropical cyclone activity in the Atlantic Basin. The report cites several factors as to why such activity is being forecast. One main factor is the situation surrounding current ENSO-neutral (El Niño Southern Oscillation) conditions. There is considerable uncertainty regarding a possible transition to a weak El Niño by the peak of the Atlantic Hurricane Season (i.e. August to October). Most of the dynamical model guidance is currently calling for either weak El Niño or ENSO-neutral conditions by the late summer/early fall. Thus, CSU believes that the most realistic scenario for the 2017 Atlantic hurricane season is borderline warm ENSO-neutral to weak El Niño conditions in the coming months.

A second factor revolves around the current unusual sea surface temperature (SST) anomaly pattern in the North Atlantic. The pattern shows a cold far North Atlantic, very warm anomalies off the US East Coast, and warm anomalies in the subtropical eastern Atlantic that extends into the tropical Atlantic. Such a pattern has historically favored a more active season. Separately, CSU is comparing these conditions in relation to the strength of the Atlantic Multi-decadal Oscillation (AMO). Based on their own analysis technique, the AMO has been in a negative phase since 2014, though it is anticipated that slightly positive AMO conditions will return later in June.