Federal forecasters just joined a chorus of weather experts predicting an active Atlantic hurricane season.
On Thursday, the National Oceanic and Atmospheric Administration released its outlook calling for a 60% chance of above-normal activity across the Atlantic Ocean during the 2020 season, which runs June 1 to Nov. 30.
Agency meteorologists put the odds of a near-normal activity level at 30%, with just a 10% chance of a below-normal season.
“We’re not seeing anything that would indicate a high likelihood of a below-normal season,” said Gerry Bell, lead hurricane season forecaster at NOAA’s Climate Prediction Center.
Historically, “average” works out to 12 named storms, six hurricanes and three major hurricanes. The past four seasons featured an above-normal storm count. If this one follows suit, a five-year streak of above-normal activity would be a record for the modern era.
In numerical terms, the 2020 outlook calls for a range of 13 to 19 named storms (including Arthur, which already came and went in the past week), of which six to 10 would strengthen into hurricanes. NOAA’s outlook also breaks out an echelon of three to six major hurricanes, hitting Category 3 or higher on the Saffir-Simpson scale with sustained winds at or above 111 mph.
And it bears repeating that those familiar wind-defined categories fail to capture the danger of storm surge and inland flooding threats.
In 1972, it only took one tropical storm to cause the worst flood in modern times on the James River. In 2004, it only took one tropical depression to unleash 1 foot of rain on Richmond. Both of the storms in question — Agnes and Gaston — peaked as low-end Category 1 hurricanes before coming our way.
The main factors cited in NOAA’s active 2020 outlook include warmer-than-normal ocean temperatures across the Atlantic, weaker winds aloft that might shear developing storms apart, and an enhanced West African monsoon.
A significant driver will be the state of ocean temperatures over the equatorial Pacific Ocean, or the El Niño-La Niña cycle. The La Niña phase, which brings cooler waters to the Pacific, tends to alter upper-level wind patterns in a way that favors more and stronger Atlantic hurricanes. El Niño does the opposite and works to suppress Atlantic storms. It’s currently in a neutral phase, and some models show it cooling into La Niña territory by the fall. An El Niño phase is the least likely scenario.
The cycle can be harder to predict during spring, so NOAA’s August update to the hurricane outlook could come with an even higher degree of confidence.
“The main uncertainty is not whether this season is going to be above normal, it’s kind of how much more active could it be if La Niña develops,” Bell said. “If La Niña develops, the activity could certainly be near the upper end of our predicted ranges.”
Studies in recent years have found that our warming climate is likely driving changes in hurricane intensification, movement and rainfall patterns, while higher sea levels gradually expand the reach of storm surge.
But the overall number of storms in the Atlantic, and how many come ashore in the U.S., varies widely from year to year without a robust long-term trend due to patterns that play out on a smaller scale than the global climate.
Other groups, from university meteorology departments to private forecasting companies, have also released outlooks in recent weeks pointing to a busy Atlantic season. Accuweather, the company that supplies the daily forecast data for the Richmond Times-Dispatch weather page, issued an outlook for 14 to 20 named storms, of which seven to 11 become hurricanes and four to six major hurricanes. Accuweather’s outlook also calls for four to six storms to affect the U.S. The NOAA outlook does not predict how many will affect land.
In 2019, there were 18 named storms, six hurricanes and three major hurricanes. Two hurricanes made landfall in the United States: Barry hit Louisiana in July, and Dorian struck North Carolina in September. The May 2019 outlook was a lower-confidence situation, favoring a near-normal range of nine to 15 named storms, four to eight hurricanes, and two to four major hurricanes.
While a higher number of storms in the ocean still doesn’t guarantee that any single one of them will track toward Virginia or North Carolina, it doesn’t bode well in a year when we’re already navigating the COVID-19 pandemic and financial concerns.
This weekend, part two of our look ahead to hurricane season will focus on how to prepare.