The tropical Atlantic is strangely silent. Will hurricane season wake up?

Eric Blake, a senior scientist at the National Hurricane Center, tweeted, “Still haven’t seen a good explanation of why the Atlantic was able to produce the strongest hurricane on record in the early season (Beryl), then shut off in mid-August!” He described the situation as “Not easy to understand folks …”

According to Philip Klotzbach, a hurricane researcher at Colorado State University, the last time the Atlantic went from Aug. 13 to Sept. 3 without cranking out a single storm was in 1968. The historically silent stretch comes in stark contrast to what experts initially called for. Most expected a “hyperactive” season, and University of Pennsylvania researchers predicted some 33 named storms — enough to blow through the National Hurricane Center’s naming list. Now it’s worth wondering if there will be even half that number.

Forecasters are starting to backtrack from earlier predictions. On Tuesday, AccuWeather lowered its seasonal forecast from 20 to 25 named storms to 16 to 20, which is still above the historical average of 14. It said it expects a busy back half of the hurricane season.

There’s a chance that something crops up in the next few days, since the Hurricane Center is monitoring three areas. But the disturbance farthest west, in the Caribbean Sea, has fallen dramatically short of once-aggressive computer model simulations. The Hurricane Center estimates it has a 30 percent chance of eventual development, with impacts probably relegated to the Yucatán Peninsula or the Bay of Campeche.

There are two other disturbances worth keeping tabs on, but both are likely to remain at sea. The first, located midway between Africa and the Lesser Antilles, has only a 10 percent chance of eventual development. A tropical wave near the Cape Verde Islands has a slightly better — 20 percent — chance of developing, but it will probably curve harmlessly into the open North Atlantic.

For now, no obvious threats are on the horizon. And that’s very, very weird.

Why has it been so quiet?

On paper, this should have been a gangbusters season. A developing La Niña is enhancing upward-moving air in the Atlantic, which should make it easier for storms to form. And Atlantic water temperatures are off the charts.

“It’s really just impossible to look at how warm the [sea surface temperatures] are in every single part of the Atlantic that matters, and not think that it just takes one to basically get its act together and wreak havoc,” said David Ryglicki, a hurricane researcher and meteorologist for MyRadar.

But despite a pristine environment ripe for explosive intensification, tropical systems haven’t been able to take advantage of the hot oceans for a number of reasons.

Tropical waves are too far north

Tropical waves, or the seedlings of storms and hurricanes, often emanate from Africa. The waves roll off the coast and over the warm waters of the tropical Atlantic, where they mature. These waves are embedded in the ITCZ, or the Intertropical Convergence Zone — a belt where colliding air from the Northern and Southern Hemispheres is forced upward, generating showers and storms.

The ITCZ wobbles about the tropics during the year, dipping south of the equator in the wintertime and lifting north in the summertime. At this time of year, it’s usually about as far north as it ordinarily gets — around 17.8 degrees north of the equator in Africa. But at present, it’s around 20 degrees North latitude. That means showers and storms are roughly 150 miles north of where they should be. That’s bringing downpours to the Sahara Desert, but it also means that tropical waves are emerging over cooler waters and ingesting drier air, causing them to fizzle before they have any chance to mature.

It’s too warm in the upper atmosphere

Record-warm waters can help fuel a tropical storm, but they can’t get storms to form by themselves. Atmospheric conditions also have to be favorable so that the heat supplied by the warm oceans can rise and help form towering storm clouds.

But temperatures in the upper atmosphere are abnormally warm, too. Klotzbach wrote in an online analysis that the warm upper levels may be suppressing thunderstorm growth. Warm temperatures aloft act as a “lid” that “caps” showers and thunderstorms and inhibits surface air from rising. That might be stifling tropical waves, and cutting back on development potential.

Harsh high-altitude winds

The same pattern bringing soaking rains to Africa is bringing enhanced easterly winds at the high altitudes over the eastern tropical Atlantic. That may be working to shred apart thunderstorm complexes before they can mature as tropical waves, tearing apart fledgling storms.

Large-scale “chain reaction” processes

Everything in the atmosphere is interconnected. Currently, a packet of thunderstorms called the MJO, or Madden-Julian Oscillation, is present north of Australia and near Indonesia. This position of the MJO has historically been unfavorable for Atlantic hurricane development, since it leads to more sinking air, and disruptive high-altitude winds, over the Atlantic. Klotzbach expects this to be the case for the next 10 days or so but, by around Sept. 15, he anticipates more favorable conditions to arrive.

When will the season wake up?

The three tropical waves now peppering the Atlantic are anemic and struggling. Weather models haven’t latched onto any prospects, and realistically, not much will happen until the MJO shifts its position about a week and a half from now.

For the back half of September, cooling temperatures at high altitudes, typical of the changing seasons, may increase atmospheric instability and support an uptick in tropical activity. The Intertropical Convergence Zone, or the thunderstorm belt from which tropical waves emanate, will meander back southward too. That would mean better survival chances for tropical waves, so the open Atlantic may have better hurricane odds then.

It’s also the time of year when “homegrown” storms become a more realistic threat — meaning chances increase for disturbances to develop in the Caribbean or Gulf of Mexico. Moreover, the gulf has a record level of “oceanic heat content,” or hurricane fuel.

As mid- to late September arrives and the calendar flips to October, autumn fall fronts crashing south could set the stage for storminess. Pockets of leftover spin along those cold fronts could serve as unexpected seedlings for storm formation in the gulf. Those instances are far more difficult to predict far in advance, underscoring the importance of remaining vigilant.

So were forecasters all wrong about a ‘hyperactive’ season?

It’s fair to admit this season to date hasn’t shaped up the way forecasters were expecting. It came in like a lion — Beryl was the most energetic storm ever observed by satellites before August. Interestingly, the season is still technically above average for season-to-date ACE, or Accumulated Cyclone Energy, a metric that tallies how much energy a season’s storms churn through.

Historically speaking, the peak of hurricane season is around Sept. 10, which means we still have halfway to go.

“If the season were to have no named storm activity through 9 September and then had an average season for the remainder of the season, it would end up classified at the high end of NOAA’s average Atlantic hurricane season,” Klotzbach wrote.

It’s becoming less likely that the 20-plus named storms that some forecasting agencies prophesied will materialize, but a hyperactive season could still occur if the back half ends up busy. While Klotzbach notes that there is “no immediate indications of a rapid ramp-up,” his outlook still calls for the latter half of hurricane season to be active. There have been numerous instances in the past when hurricane activity paused and then roared back to life.

Jason Samenow contributed to this report.