A tropical depression forming in the Gulf of Mexico over the Memorial Day weekend is looking more and more inevitable.
On Thursday, National Hurricane Center forecasters upped the odds of a storm developing from a system now near the Yucatán Peninsula to 70 percent over the next two days and 90 percent in five days. Computer models also agreed on a likely scenario: a depression or named storm making landfall along the Florida Panhandle or Louisiana coast sometime Monday.
While some models suggest the system could become a Category 1 hurricane, University of Miami hurricane researcher Brian McNoldy said it's still early to reliably make a call on intensity.
"The human subjective input to that is don’t read too much into that," he said. "They can easily be wrong at this point because it’s still a very disorganized swirl over the Yucatán."
A hurricane hunter plane is scheduled to investigate the system Friday.
South Florida's biggest threat remains heavy rain, which could begin as early as Friday. Flooding is also possible after nearly a month of heavy May rain.
"The grounds are fairly saturated right now," National Weather Service Miami meteorologist Andrew Hagen said. "I wouldn’t say they’re extremely saturated, but they are fairly saturated so areas that receive heavy rainfall could see some flooding issues."
The slow-moving system began drawing meteorologists' attention last week when computer models began to suggest the swirl of low pressure near Belize could gain steam, said AccuWeather senior forecaster Dan Kottlowski. While the official hurricane season doesn't start until next Friday, Gulf waters are already warm enough to fuel a tropical cyclone if atmospheric conditions are favorable.
A preseason storm is uncommon, but not unheard of, and usually forms in May. At least eight have occurred in the Atlantic over the past decade, including Tropical Storm Arlene in April 2017 over the central Atlantic.
The system's proximity to the coast and wind shear have so far kept it in check and left it a lopsided mess. But upper level winds are expected to move east, forcing it north across warm waters.
"As the low pressure moves away from land, then it will have nothing but the open part of the Gulf to move over," Kottlowski said.
If the system stays lopsided, it could become a subtropical system, with stronger winds whipping around the storm's edges rather than the center where winds are strongest in a tropical storm. Subtropical systems are similar to tropical and produce the same hazards — wind and heavy rain — but are more elliptical and lack a warm center.
"You’re still going to get the hazards of winds and heavy rain. But it’s just kind of lopsided, so the strongest winds will not necessarily be near the center of the system," said hurricane center spokesman Dennis Feltgen.
Heavy rain is a concern for South Florida because so much has already fallen this month. In some places, totals are three times the monthly average, a dramatic leap from April when rainfall was well below average, left the region abnormally dry and fueled wildfires across the Big Cypress National Preserve.
In preparation for possible flooding, the South Florida Water Management District will continue to keep canal levels in Broward and Miami-Dade counties low, spokesman Randy Smith said Thursday.
"We’ve had a very large amount of rain starting on May 13th, so we’ve been running pump stations and gate operations basically 24 hours a day," he said. "We’ll continue that 24/7 until we can get through this."
The Gulf Coast should also look out for heavy rip currents, forecasters said.