A “potential tropical cyclone” seen via satellite on Friday morning. It may become Tropical Storm Humberto if it continues to develop. (NOAA/TropicalTidbits.com)
By Matthew Cappucci and

Matthew Cappucci

Meteorologist, Capital Weather Gang
Andrew Freedman

Andrew Freedman

Editor focusing on extreme weather, climate change, science and the environment.

September 13 at 11:11 AM

Less than two weeks after being devastated by Hurricane Dorian, Grand Bahama and Abaco islands are under tropical storm warnings on Friday morning. The system in question, currently classified as a “potential tropical cyclone,” is 140 miles southeast of Great Abaco.

The system is forecast to gradually become better organized and move ever closer to the Northwest Bahamas today and tonight. By Saturday, it is likely (90 percent odds) to achieve tropical storm status, which would earn it the name Humberto.

After that, the United States could be next in line, although uncertainty abounds.

Most likely: A brush with the Florida coast

The most likely scenario at this point calls for a close shave or a pass just off the Florida coast.

Between its current location and Florida lies the Northwest Bahamas, where recovery efforts are underway after the direct hit from Hurricane Dorian, one of the strongest Atlantic storms ever to make landfall. The developing storm is likely to bring heavy rains and gusty winds to the storm-weary region, which could be disruptive for recovery operations.

The National Hurricane Center mentioned on Friday morning that “this system is not expected to produce significant storm surge in the northwestern Bahamas.” In contrast, Hurricane Dorian is thought to have produced as much as a 23-foot storm surge in that region.

The system looks to intensify into Humberto by daybreak Saturday morning, around which point it could be located east of Miami. However, the Hurricane Center estimates a 10 percent chance of tropical-storm-force winds — sustained at 39 mph or greater — reaching the city.

Farther north, impacts could be a bit greater depending on how close the center of circulation gets to the coast. A tropical storm watch has been posted from Jupiter Inlet to the Flagler/Volusia County line. Potential tropical-storm-force winds, heavy rainfall, rip currents and isolated tornadoes are possible along this stretch of coastline if the current forecast track is realized. A couple inches of rain would also be possible.

Elsewhere, if this storm track were to verify, the bulk of the precipitation should remain relegated to the immediate shoreline or just offshore.

Even in the most likely “brush with the coast” scenario, forecasters are not confident about the track of soon-to-be Humberto past Florida. Will it recurve out to sea? Possibly. There is a moderate chance of it scooting out to sea after flirting with the Sunshine State.

Because the storm is so weak right now, with a poorly defined circulation center, computer models are having a hard time predicting the storm’s track beyond 48 to 72 hours.

There’s a nonzero threat of it being forced to ride up against the East Coast, similar to Dorian, or even driven inland somewhere. The longer it stays over water, the better the chance it has to intensify into a hurricane. The official forecast is trending more with the offshore idea, but the Hurricane Center cautions that uncertainty is higher than usual and likely will be until the storm organizes further.

Also possible: A Florida direct hit

Some models bring the developing system inland into the Florida peninsula. This scenario is less probable than the near-shore track currently expected. In this scenario, the fledgling disturbance could make landfall as a tropical storm sometime over the weekend between the Treasure Coast and Daytona Beach. If landfall were to occur, it’s unlikely that the system would be above tropical storm intensity at that point, given a limited window for development over open water.

This storm scenario could bring winds gusting over 40 mph, 2 to 4 inches of rainfall with localized 5+ inch amounts, and a low-end tornado risk to parts of Florida. Who gets what is unclear at this point, since specific hazards are highly dependent on the track and storm intensity at that point. In any case, this would not be a “board up and get out” event.

It would be more a “don’t drive through flooded roads” and “don’t be swimming in the surf” type of system.

Also possible: A ‘see ya later,’ out to sea scenario

It’s also possible that, after impacting the Northwest Bahamas, the system could pass out to sea. The European model advertises this solution. However, this comes just a couple runs after the European model was calling for a New England landfall. When the models exhibit a wishy-washy “windshield wiper effect,” vacillating between wildly different projections, it’s indicative that we’re dealing with a very low-confidence forecast.

However, a solution that brings the storm entirely out over the Atlantic is certainly possible.

Group of simulations from American (blue) and European (red) computer models from Friday. Each color strand represents a different model simulation with slightly altered input data. Note that the strands are clustered together where the forecast track is most confident but diverge where the course of the storm is less certain. The bold red line is the average of all of the European model simulations, while the bold blue one is the average of all the American model simulations. (StormVistaWxModels.com)

Unlikely: A jaunt to the Gulf of Mexico

Initial model runs several days ago had alluded to the potential passage of this system over Florida and eventually into the Gulf of Mexico. In their early depictions, the tropical wave would grow some over the northeast gulf, making a run at the Florida panhandle, coastal Alabama, Mississippi or even Louisiana. This option is no longer on the table, as most computer models no longer depict it as the lineup of weather systems that will steer the storm would seem to prevent so much westward movement.

Why the uncertainty?

Ever play “pin the tail on the donkey”? It’s probably not easy to do blindfolded. That’s sort of how we have to go into this forecast, since computer models can’t get a good handle on the future location and intensity of what is likely to become tropical storm Humberto until it is better organized. The level of organization greatly affects how nearby weather systems interact with the storm, since weaker systems more sensitive to winds in the mid-levels of the atmosphere, compared with stronger storms that are directed more via upper-level winds.

Odds are we won’t have a better grasp on the storm track for another 24 to 36 hours. By evening Saturday, a near-surface center should have emerged. At that point, models will be able to say “found it!” and have a better idea of how the system will interact with its surroundings.

“The weirdest aspect … I see is the absolute disagreement in model forecasts, even in the 2-3 day lead time,” wrote CWG’s tropical weather expert Brian McNoldy. “So far, it has been slow to congeal.” He described the thunderstorm cluster as a “mess” on radar and satellite but hopes that a Hurricane Center reconnaissance plane en route will offer more insight into the storm’s inner workings.

The best advice at this point? Stay tuned. Be aware but not alarmed. This will not be a top-tier storm. But it still merits our attention. After all, we’re in the heart of the 2019 hurricane season.