Why this could end up the least-active hurricane season in 13 years

In an updated outlook released this week, researchers at Colorado State University are predicting a particularly muted Atlantic hurricane season, even indicating a possibility that no major storm makes landfall in the United States. It would be the least-active season in at least 13 years.

Only nine named storms are expected basin-wide, according to the group, notably lower than the annual average of 14.4. One relatively meager tropical storm, Arthur, already skimmed along the Texas coastline from June 17 to June 18.

Of the remaining eight storms that CSU forecasts will form this year, four are expected to become hurricanes, and one should attain Category 3 or greater strength, making it a major hurricane.

Because this is the forecast for the entire North Atlantic, that makes the odds of the U.S. getting hit relatively low. In fact, CSU projects only a 17 percent chance of a major U.S. landfall. That’s down from a typical 43 percent chance any given season.

In another sign of a turned-down season, the group’s predictions for Accumulated Cyclone Energy (ACE) run just 40 percent of what’s typical for a season. ACE can be thought of as the seasonal total of all the heat energy extracted from the oceans and expended by storms on producing strong winds. Especially encouraging is how comparatively little ACE is forecast west of 60 degrees longitude, which is where the U.S. is located.

What’s driving the quiescence? It’s due to the burgeoning El Niño pattern, which is expected to become the strongest on record.

El Niño begins as a warming of water temperatures in the eastern tropical Pacific. That heats the air above, causing it to rise. The rising air is expected to generate more tropical systems in the Pacific, which is why it is likely to see a potentially hyperactive season.

But what goes up must come down, and that rising air is mirrored by subsidence, or sinking, in the Atlantic. That will squash many attempts at tropical cyclone formation, reducing the overall number of storms.

Moreover, El Niño patterns amplify wind shear, or disruptive changing winds with height. That will shred some disturbances before they can even grow into named storms. Tropical cyclones that do become established may be knocked off-kilter by harsh upper-level winds, reducing their intensity.

Water temperatures across the Atlantic are also closer to average, rather than the red-hot anomalous warmth that’s been characteristic of the past few hurricane seasons.

Despite the encouraging signs that suggest fewer relative storms, it’s important for coastal residents not to let their guard down. After all, hurricane season is still hurricane season.

“As with all hurricane seasons, coastal residents are reminded that it only takes one hurricane making landfall to make it an active season,” wrote Colorado State forecasters.

The 1992 Atlantic hurricane season, for instance, was anemic on paper — when measured by total activity. Accumulated cyclone energy was 38 percent below average. Only one major hurricane formed.

But that was Category 5 Hurricane Andrew, which lay siege to South Florida and the southern suburbs of Miami.