MIAMI — The Atlantic's most powerful hurricane ever outside the Gulf of Mexico and the Caribbean is expected to pound Florida with damaging winds, but where, and just how bad the state gets hit, remains unclear.

Irma has been churning west, on a path that began slamming the Leeward Islands on Tuesday night, as it rolls toward the Virgin Islands and Puerto Rico. It's being steered by a high pressure ridge that in the coming days is expected to collide with a low pressure trough moving across the U.S. When they meet, the ridge should weaken and allow Irma to sneak north, determining where the hurricane's fiercest winds land. But so far, models have not been able to agree on where that critical turn happens.

Put Florida's skinny peninsula in the path of such a monster storm — hurricane winds stretch 120 miles, Florida is just 160 miles wide — and it means storm conditions could be widespread.

"We are going to get impacts from this hurricane. There is no doubt about that right now," said University of Miami hurricane researcher Brian McNoldy. "The only question is how bad will it be at a given location with the competing weather systems."

Forecasters said Tuesday evening that models generally agree during the next 72 hours, but after that they begin to spread, raising uncertainty. Due to track errors ranging from 175 to 225 miles, they warned that more attention should be paid to the forecast cone.

In Florida, the increasing threat triggered evacuation orders in Monroe County for all residents and visitors. Miami-Dade County said it would likely issue orders Wednesday for barrier islands and the coast. Schools in Miami-Dade, Broward and Monroe counties also will be closed.

Across the Caribbean, islands are likely to take a beating. On St. Thomas, where John Morales of NBC6 reported surface winds forecast for 173 mph, visitors took to Twitter to ask airlines to send more planes since departing flights were fully booked. Storm surge in the Turks and Caicos and southeastern Bahamas could reach 15 to 20 feet, with other islands in Irma's path expected to get anywhere from a foot to 11 feet, forecasters said.

In Puerto Rico, the electric company warned the island could be without power for four to six months while the government prepared to open 456 shelters capable of housing more than 62,000 people. The Turks and Caicos has ordered Salt Cay, its southernmost inhabited island, evacuated beginning Wednesday. In Cuba, where Matthew razed some neighborhoods last year, officials urged caution, but took a more notable low-key approach.

The Leeward Islands were to get hurricane force winds Tuesday night, forecasters said, with Puerto Rico and the Virgin Islands coming under dangerous conditions Wednesday. Next in line: the Dominican Republic on Thursday.

While the storm was steaming west at about 15 mph, models show Irma coming nearly to a dead stop when it begins to make its northward turn, increasing threats from dangerous winds and rain. Irma is not expected to deliver the record-shattering amounts of rain Harvey dumped on Houston, but any lingering raises risks.

"When it stops to make that right turn and then starts to move north, we're not going to get it moving full steam ahead like it is now, which is not good because when you have a strong storm, you want it to be over you as short a time as possible," McNoldy said.

In their 8 p.m. advisory Tuesday, forecasters said Irma was located 85 miles east of Antigua, moving west at 15 mph. Maximum winds remained at an astonishing 185 mph, with higher gusts and deteriorating conditions expected to develop.

While it's still not known what part of Florida will take the brunt, officials across the state made clear that Irma poses a very dangerous threat. Gov. Rick Scott has declared a state of emergency for all 67 counties and ordered all 7,000 members of the state's National Guard to report to duty on Friday. Highway tolls across the state were lifted at 5 p.m. Tuesday.

Monroe County said there will be no roadblocks into the Keys before the storm, to allow property owners and family members to help out with evacuations. However, plans should be completed quickly.

"If ever there was a storm to take seriously in the Keys, this is it," Monroe County Emergency Management Director Martin Senterfitt said. "The sooner people leave, the better."

Wind speeds could fluctuate over the next day or two, but forecasters say Irma will likely remain a very dangerous Cat 4 or 5 storm as it heads westward.

In addition to a state emergency, Scott said President Donald Trump issued a federal emergency in advance of Irma's arrival. The state also began coordinating rescue efforts that include 13 helicopters and 1,000 high-wheeled trucks capable of driving through high water. North Carolina's National Guard is also on standby to help with evacuations from the Keys, if needed, and the National Guard is lining up an additional 30,000 troops, 4,000 trucks and 100 helicopters to provide additional aid, the governor's office said in a statement.

"It is important for all Floridians to keep an eye on this incredibly dangerous storm. Do not sit and wait to prepare. Get prepared now," Scott said in an evening press briefing. "This storm has the potential to devastate this state and you have to take it seriously."

The Florida Highway Patrol and Department of Transportation are also on standby to help with evacuation efforts, he said.

Utilities have been asked to begin posting outage and restoration information as the storm hits and are contacting other utilities to help out with repairs, Scott said in a statement. No fuel shortages have been reported, Scott said, but the state has contacted fuel suppliers in case emergency supplies are needed. The state is also working to identify which stores have sold out of bottled water. The state insurance agency has also authorized early prescription refills.

Across the mainland, the U.S. Army Corps of Engineers announced it would begin releasing water from Lake Okeechobee to the St. Lucie and Caloosahatchee rivers, potentially raising the risk of damaging algae blooms.

"We want to be ready for the heavy precipitation from Irma," said Col. Jason Kirk, Jacksonville District commander. "We anticipate direct rain over the lake could add a foot to the water level. We've seen basin runoff from past events cause the lake to rise 3 feet over the span of a month. We want to do all we can to ensure we have as much storage as possible for Irma."

The South Florida Water Management District has also begun lowering canals to make room for heavy rain, flushing as much water as possible starting in South Dade. In a morning news conference, chief engineer John Mitnik said he expects the storm to dump between 8 and 10 inches of rain, but where it falls depends on Irma's track. Mitnik said South Florida's extensive canal system is also capable of moving water quickly, however local drainage depends on flood controls set up in neighborhoods and subdivisions.

"If your particular subdivision was designed to have street flooding, then that's what you'll expect to see," he said.

Timing is another issue.

"If you take 8 to 10 inches over several days, or compact it in 30 minutes, those are two different things," he said.

Over the last week, Irma's repeated eyewall replacements have propelled the storm's growth. Eyewall replacements are a common structural change for such massive storms that can initially weaken the storm. In Irma's case, the hurricane quickly rebounded, increasing intensity as it expanded its reach. While they play a key factor in hurricane intensity, forecasters say they remain difficult to predict.

Meanwhile, Tropical Storm Jose formed in the far east Atlantic Tuesday morning. At 5 p.m., the storm was located about 1,400 miles east of the Lesser Antilles, moving west, northwest at 12 mph. Sustained winds reached 45 mph, with Jose expected to reach hurricane strength by Friday, forecasters said. So far, Jose poses no threat to land.