Average number of hurricanes forecast for 2016

Published 7:00 am Tuesday, April 19, 2016

Last week was notable in the world of seasonal, extended range hurricane forecasting for two reasons. On April 14th, Dr. Philip Klotzbach of Colorado State University issued his annual spring outlook for the upcoming 2016 hurricane season. Two days later, Dr. William Gray, a pioneer in the field of seasonal hurricane forecasting and Dr. Klotzbach’s mentor, passed away at the age of 86.
Gray, a professor of atmospheric science at Colorado State University for over fifty years, issued the first prediction of the number of tropical storms in an upcoming hurricane season in 1983. Gray’s statistical model was based on relationships he had discovered between major atmospheric and oceanic patterns and trends in the months preceding the season and the number of Atlantic hurricanes that subsequently occurred.
The approach was initially met with skepticism from many atmospheric scientists, but Gray and his students and collaborators persisted, refining the predictive model over the next several decades. The endeavor gained more acceptance, and others entered the field. Now, in addition to Colorado State, seasonal tropical cyclone forecasts are issued by the U.S. National Oceanic and Atmospheric Administration and a number of private consulting firms.
Last year at this time in April, Klotzbach and Gray were predicting a below-average number of hurricanes in 2015.
They were right. Wind shear in the tropical Atlantic, associated with what was to grow into a huge Pacific El Nino, helped put a lid on hurricane development last season. Klotzbach and Gray predicted that three hurricanes would form in the Atlantic in 2015. Four hurricanes ended up forming in the Atlantic basin in 2015, two below the long-term average of six per year.
In last week’s predictions for the 2016 Atlantic hurricane season, Klotzbach forecast a slight uptick in activity as he expects twelve tropical storms to form and five of those to mature into full-fledged hurricanes.
The oceanic and atmospheric patterns associated with the above-average tropical Pacific upper ocean temperatures known as El Nino are finally weakening after almost a year. There are even signs that the tropical eastern and central Pacific Ocean may flip into the opposite, cool phase known as La Nina. In fact, last week NOAA’s Climate Prediction Center issued a La Nina Watch, saying that there is an increasing chance of La Nina by the second half of 2016.
Regardless of whether El Nino is replaced by La Nina, or simply weakens, wind shear over the tropical Atlantic should be less this summer and fall than last year, which will be more conducive for hurricane development.
However, sea surface temperatures in the northern reaches of the Atlantic are much below normal. Indications are that this pattern of cooler than average upper ocean temperatures may expand over the next few months to include the main hurricane development region in the Atlantic. That would tend to inhibit storm development.
These conflicting predictors led Klotzbach to note that this season’s forecast has even more uncertainty than usual.
And, as Klotzbach and other seasonal forecasters are always quick to note, if there’s only one hurricane and it makes landfall, the people affected will consider the season a major one.

By Skip Rigney

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