Wind and storm surge watches went up across the Florida Gulf coast late Friday as Alberto continued creeping north.
The western tip of Florida's Panhandle was at the center of the projected impact zone and while Alberto's strongest winds were expected to stay well offshore until then, forecasters cautioned the path potentially could shift over the next few days. Either way, much of the state, including the Florida Keys and mainland South Florida, was likely in for a holiday weekend drenching from a storm that formed before hurricane season officially begins on June 1.
Along the the southwest coast, surf and surge could also pile seawater atop the rain. And once it does makes landfall, forecasters were concerned it could stall and trigger worse flooding.
"When it gets inland, it will be a slow mover, so this could be a horrific flooding event up there," National Hurricane Center spokesman Dennis Feltgen said.
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In an 11 p.m. advisory, forecasters said the storm, located 110 miles southeast of Cozumel, Mexico, was heading east about 5 mph with sustained 40 mph winds. The storm was expected to turn north overnight and into Saturday morning, passing near the Yucatan coast before approaching the Gulf coast Monday.
Forecasters said they expected dry air to keep the storm from strengthening into the hurricane, but warned that could change.
Broad winds that now extend 140 miles from the storm's center could help push a two to four-foot storm surge across parts of the Gulf coast, where a storm surge watch extended from Florida's Big Bend to the mouth of the Mississippi River. Tropical storm conditions may be felt within 48 hours along the Panhandle to eastern Louisiana, forecasters said.
Heavy rain remains the storm's biggest threat, with the Keys expected to get four to eight inches. Up to 12 inches could fall in some locations. Between four and six inches could fall along the coast between Fort Lauderdale and Flamingo, according to the National Weather Service, which issued a flood watch for South Florida from 8 a.m. Saturday to 8 p.m. Sunday.
Cuba and the Yucatán Peninsula could get 10 to 15 inches, with up to 25 inches in harder hit locations, increasing the risk of dangerous flash floods.
Forecasters upped the storm's status on Friday after local buoys and ship readings reported higher winds. It was designated subtropical because strong upper level winds continue to shear the top, leaving it lopsided. A subtropical system packs the same hazards as tropical storms — heavy rain and wind — but lacks the warm center. Stronger winds also wrap around the storm's edges, rather than the center.
As it moves north, the shear is expected to subside and allow the storm to transition into a more dangerous tropical storm over warm water.
"In the northern Gulf, the upper winds won’t be an issue any more. The storm will get better organized so we expect it to strengthen," Feltgen said. "You certainly can’t rule out that it could become a hurricane."
Because the storm's center is so messy, forecasting the track also remains difficult. A large ridge to the east should turn it north for the next 24 hours. Saturday and Sunday, it's expected to follow a steadier northern track and begin turning northwestward Sunday night and Monday, with its speed picking up as it nears the Gulf coast Monday night.
Wind shear over the next day will likely keep it from intensifying, but new model runs now show the winds weakening a little sooner than previously. Forecasters said they expect the storm to now peak Monday morning when the shear slows. They expect dry air to keep it from further strengthening, but warn that could change.
Forecasters also warned that the location of the storm's center far from the Florida coast could be misleading.
"Don’t let that fool you because the wind flow on the east side may bring very rough surf," said AccuWeather senior meteorologist Dan Kottlowski. "As it becomes more persistent, it will create a pileup of water, so the concern is for southwest Florida, or the west coast to Apalachicola Bay, which could get a big inundation of water because of the constant wind blowing and a lot of places are very prone to flooding."
With the storm sucking so much moisture from the Caribbean, South Florida should get ready for a soggy holiday weekend, with tornadoes possible as conditions worsen.
"As it tracks north over the Gulf over the next couple of days, our impacts are going to be pretty much the same: heavy rain with potential flooding," said Robert Molleda, warning coordination meteorologist for the National Weather Service's Miami office.
Over the last month, parts of South Florida including Miami-Dade and Monroe counties have been pounded with rain, pushing totals to more than two and three times usual May amounts and leaving the ground saturated. The bulk of the heavy rain should fall Saturday and Sunday, he said.
Gusty winds and rough seas should increase Saturday with rip currents expected on both coasts. South Florida won't likely be included in any watches, Molleda said, but that could change.
"Any significant deviation from this forecast, especially to the east, could change that," he said.
Miami Herald reporter Martin Vassolo contributed to this report