‘Rare’ Twin Storms To Threaten U.S. East Coast: See FL Timeline

As Hurricane Gabrielle moves past the Bahamas and toward the Azores - well away from the U.S. - two new tropical threats are brewing in the Atlantic and could organize in close proximity to each other and the East Coast over the next week, according to the latest forecasts.

Some models suggest that the two systems “could interact with each other resulting in a very challenging forecast,” Denis Phillips, chief meteorologist for Tampa Bay 28, wrote in a Facebook post. “Models show this phenomenon occasionally. It happens, but it's rare. It's called the ‘Fujiwhara Effect.’”

The Fujiwhara Effect happens “when two hurricanes spinning in the same direction pass close enough to each other, they begin an intense dance around their common center,” according to the National Weather Service. “If one hurricane is a lot stronger than the other, the smaller one will orbit it and eventually come crashing into its vortex to be absorbed.”

If the storms are similar in strength, they might merge as they gravitate towards each other or spin around each other before shooting off in different directions, NWS said. “In rare occasions, the effect is additive when the hurricanes come together, resulting in one larger storm instead of two smaller ones.”

The storms in the Atlantic currently being watched by forecasters, Invests 93L and 94L, could bring rain, wind and dangerous surf conditions to parts of Florida next week.

The peninsula, including northeastern Florida, has a medium chance of tropical rain and winds between Sept. 29 and Oct. 1, according to AccuWeather. The panhandle has a low chance of seeing effects from these systems.

Both have high chances of strengthening into a tropical depression or storm over the next week, the National Hurricane Center said.

A tropical rainstorm formed late Tuesday in the central Atlantic and could impact Bermuda as a hurricane by early next week, AccuWeather forecasters said in an outlook released Wednesday. Meanwhile, a tropical wave near the Lesser Antilles could also become a named tropical system near the Bahamas as early as late this week.

"We predicted this burst of tropical activity in late September, after an unusually quiet stretch in the tropics during the climatological peak of the season," said AccuWeather lead hurricane expert Alex DaSilver, adding that hostile atmospheric conditions across much of the Atlantic basin prevented tropical waves from developing in late August and early September.

He continued, "Disruptive wind shear and dry air have eased, allowing tropical waves to organize into storms. We will likely see Humberto and Imelda form before the end of the weekend.”

Invest 93L, an area of low pressure causing showers and thunderstorms several hundred miles east of the Leeward Islands on Wednesday, has a 90 percent chance of developing over the next two days, NHC forecasters said.

A tropical depression is likely to form later Wednesday or Thursday as it moves west-northwest across the ocean, the agency said.

Currently, the storm is forecast to pass between Bermuda and the U.S. East Coast, and it is expected to bring some rain and gusty winds to Bermuda starting Sunday evening.

“This storm will likely create rough surf and rip currents that could impact beaches across the Bahamas and the East Coast starting this weekend,” DaSilva said. “People in Bermuda and along the East Coast should monitor forecast updates closely. The storm may develop quickly.”

Meanwhile, forecasters are also watching Invest 94L, a tropical wave over the northeastern Caribbean Sea, which is producing disorganized showers and thunderstorms and has tracked farther west than any other system this season.

The system has an 80 percent chance of developing into a tropical depression over the next seven days, the NHC said.

“[Invest] 94 is the one to watch. It's messy and disorganized,” Phillips wrote. “Big rainmaker for Puerto Rico and the Virgin Islands. Early next week, it will probably be impacting the Eastern Bahamas. Just too soon to forecast how close it gets to the US East coast. Odds are higher it impacts the [North Carolina] coast than Florida, but again, too early to make a definitive call. (But that's the way I'm leaning now).”

This wave is expected to move west-northwestward at 15 to 20 mph, spreading heavy rainfall and gusty winds into Puerto Rico and the Virgin Islands on Wednesday, and across the Dominican Republic beginning Wednesday night, according to forecasters.

At the same time, Hurricane Gabrielle, once a Category 4 storm, will bring hurricane conditions to the Azores by Thursday, AccuWeather said. The system will then weaken, losing wind intensity as it heads toward western Europe, which it will impact as a tropical rainstorm this weekend.