• Bryan Norcross

New Hurricane Season forecast predicts a busier than normal season

Colorado State University has released its first hurricane-season forecast of 2020. The prediction is that 16 named storms will form in the Atlantic, the Caribbean, or the Gulf of Mexico, 8 of those will be hurricanes, and 4 of the hurricanes will reach Category 3 or higher strength.

These numbers are all higher than average, based on the thirty years from 1981 to 2010, which is the official baseline. Since 1995, however, we have seen more storms on average. This new prediction is close to the average amount of tropical development over the past 15 years.

Seasonal hurricane forecasts were pioneered at Colorado State by Dr. Bill Gray in 1984. Today, the forecasts are made by a team of Dr. Gray’s former students led by Dr. Phil Klotzbach.

The team has identified three atmospheric and oceanographic measurements they can look at to give them an indication of how favorable conditions will be this summer for storms to develop. Their forecasting model uses water temperatures in the Atlantic and the western Pacific, plus the upper-level winds across that Atlantic that can inhibit storm organization.

Both of the ocean-temperature measurements indicate somewhat favorable conditions for storm development, while the upper-level winds appear slightly unfavorable. Taken together, they lead to a forecast slightly above the long-term average.

For the first time this year, the CSU forecast comes with estimates of its accuracy. They ran their forecast scheme on spring weather conditions in past years and applied the statistics to this year’s forecast. The calculation is that the number of named storms this season will fall between 13 and 19, with about 2/3 certainty.

It turns out that there is a fundamental challenge making hurricane-season forecasts this time of year. It’s called the Spring Predictability Barrier. Because whether an El Niño develops or not has such a big effect on the number of tropical systems that form in the Atlantic, making a good prediction, in effect, comes down to forecasting the state of a potential El Niño.

Because the factors that trigger El Niño, which creates unfavorable winds over the tropical Atlantic, are so subtle in the spring, El Niño forecasts are notoriously unreliable this time of year. As we get closer to summer, it will become clearer how El Niño is going to turn out.

The evidence that we have, based on a variety of computer models, indicates that El Niño will not be a factor this year, but we have to take these forecasts with something of a grain of salt.

The main point is, forecasts made this time of year should be taken as interesting science and nothing more.

The biggest value of pre-season forecasts is that they remind us that Hurricane Season is coming in just two months. Since we are all stuck at home, it’s a good time to talk with the family and make a good hurricane plan.

© 2019 by Bryan Norcross Corporation

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