What’s the Deal? The Reason behind Increasing Atlantic Seasonal Hurricane Forecasts

It’s early July, and the Atlantic has already had 3 named storms. While early summer season hurricane activity does not necessarily correlate with overall numbers of hurricanes in the Atlantic, seasonal forecasts have generally been increasing over the past few months. For example, Colorado State University (CSU) recently updated its summer seasonal hurricane predictions. In their forecast issued in early April, they predicted 4 hurricanes. In early June, they predicted 6 hurricanes, and their updated summer hurricane forecast issued earlier today predicted 8 hurricanes. Many other forecast groups are also now calling for an above-average season (Figure 1).

There are two primary reasons why CSU and several other groups have increased their forecasts. The first is due to a diminishing chance of El Niño developing this summer and fall. Many forecast models earlier called for El Niño to develop in time for the peak of the Atlantic hurricane season from August-October. El Niño is warmer than normal water in the eastern and central tropical Pacific and forces stronger than normal upper-level westerly winds that tear apart hurricanes in the tropical Atlantic and especially in the Caribbean. The absence of El Niño tends to lead to conditions that are more conducive for Atlantic hurricanes to form.

When groups put out early seasonal forecasts in late March and early April, the tropical Atlantic was somewhat cooler than normal. Winds across the tropical Atlantic have generally been weaker over the past couple of months, leading to considerable anomalous warming since April. At the beginning of July, sea surface temperatures in the tropical Atlantic are warmer than normal, providing more fuel for developing tropical cyclones that live off of warm ocean water. In addition, warmer water is also associated with a more unstable environment, helping to fuel thunderstorms that are the building blocks of hurricanes.

The United States has been on a remarkable lucky streak of 11 years with zero major (Category 3-5 on the Saffir-Simpson wind scale) hurricane landfalls, breaking the old record of eight years set from 1861-1868. Hurricane Matthew nearly broke the landfall drought streak last year though, as it came within 100 miles of the east coast of Florida as a major hurricane. This streak of good luck of major hurricane avoidance cannot last forever, however. Regardless of how much activity is predicted, now is the time to prepare for this year’s hurricane season.

2017 Atlantic Hurricane Season Predictions
Figure 1: Publicly-available seasonal hurricane forecasts from government agencies, universities and private forecasting companies as of the end of June 2017. Forecasts available on http://www.seasonalhurricanepredictions.org.

About the Author:
Dr. Phil Klotzbach has received national and international attention for his work in researching weather patterns and forecasting hurricanes. For the past 10 years, Dr. Klotzbach has been lead author on Colorado State University's Atlantic basin hurricane forecasts, which were founded by his late esteemed colleague Dr. William Gray.  

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