(This story, first published Friday, will be updated throughout Saturday morning. It was last updated to incorporate the 8 a.m. National Hurricane Center advisory as well as new model information, offering greater confidence Florida's west coast is most at risk.)
The extraordinarily large and intense Hurricane Irma is drawing ever closer to the Florida peninsula, and the first rain bands are pivoting across extreme southern portions of the state. A hurricane catastrophe has become nearly unavoidable; it's only a matter of what areas are hardest hit and how severe the damage will be.
Computer model information overnight Friday and early Saturday suggest Irma is most likely to track up Florida's west coast. Although small shifts in the track are still possible, the Florida Keys, Naples, Fort Myers and Tampa Bay area seem likely to be hit hard.
Irrespective of the storm's exact track, damaging winds are likely to blast most if not all of the Florida peninsula. With the storm still more than 200 miles away, Miami International Airport clocked a wind gust of 57 mph just after 7:30 a.m. Saturday.
"Irma is likely to make landfall in Florida as a dangerous major hurricane, and will bring life-threatening wind impacts to much of the state," the National Hurricane Center said.
The Hurricane Center had hoisted hurricane warnings for much of South and Central Florida on both coasts, reaching north of Tampa and Melbourne. Hurricane watches extended somewhat farther north.
Landfall from the storm is most likely to occur sometime Sunday, when Irma's most destructive winds will move ashore, but tropical-storm-force winds are expected to progress up the Florida peninsula during the day Saturday.
A storm-surge warning was also issued for much of the South and Central Florida coastline, past Tampa on the west coast and Melbourne on the east coast, because of the potential for water to rise up to 6 to 12 feet above normally dry land at the coast. The Hurricane Center said this would bring the risk of "dangerous" and "life-threatening" inundation and that the threat was highest along Florida's southwest coast and in the Florida Keys.
"Few people alive have experienced a storm like this," wrote Bryan Norcross, a hurricane specialist at Weather Channel. "It is reminiscent of the great hurricanes that unleashed their fury on Florida in the first seven decades of the 20th Century."
By early next week, Georgia, South Carolina and the interior Southeast could be in the storm's crosshairs
In its 8 a.m. update, the Hurricane Center said the storm was positioned 225 miles south of Miami, chugging along to the west-northwest at 12 mph.
As the eye of the storm moved over the north coast of Cuba early Saturday, its circulation was disrupted some by the land mass which caused the storm to weaken to a Category 4, with peak winds of 130 mph. On Friday night, it had briefly regained Category 5 intensity, packing 160 mph winds, just before making landfall on the Camaguey Archipelago of Cuba. It became the first Category 5 hurricane to make landfall in Cuba since 1924.
The Hurricane Center said to expect fluctuations in the storm's intensity through Sunday but that, in most scenarios, "Irma is expected to remain at least a Category 4 hurricane until landfall in Florida."
It urged residents of Florida to rush preparations to completion.
"This hurricane is as serious as any I have seen," tweeted Eric Blake, a forecaster at the Hurricane Center. "No hype, just the hard facts. Take every life saving precaution you can."
Meanwhile, Hurricane Katia made landfall along in Mexico's Gulf Coast Friday evening. And on Saturday, Hurricane Jose, which was nearly a Category 5, could hit some of the same small islands in the northern Lesser Antilles ravaged by Irma, including Antigua and Barbuda. Hurricane warnings were in effect.
Potential effects on Florida
Several storm scenarios are possible in Florida, depending on the exact track Irma takes, but they are all disastrous due to Irma's size and strength.
Hurricane-force winds expand 70 miles from the center, and tropical-storm-force winds expand 195 miles from the center. This implies that the entire peninsula, which is about 150 miles across, will be exposed to tropical-storm-force winds and most or all of it to hurricane-force winds.
Norcross, the meteorologist who became a hero in South Florida for guiding the region through Hurricane Andrew, called the threat "EXTREME."
Tropical-storm-force winds are expected to reach South Florida between Saturday morning and early afternoon as Irma approaches from the south-southeast.
Then, the all-important northward turn is still expected to take place early Sunday, when the storm would make landfall and unleash its worst effects. The most destructive winds and largest storm surge usually focus immediately to the northeast of where the center comes ashore. So exactly where the northward turn occurs is a critical question for Florida.
As of Saturday morning, the most likely scenario based on computer-model guidance was that the storm will track along or just inland of Florida's west coast. Landfall is most likely to occur somewhere on the west coast but the Hurricane Center said "it is extremely difficult to pinpoint exactly where the center might move onshore."
Models, however, can shift. The average error in hurricane forecasts 36 hours before landfall is about 50 (or one-third of the width of the peninsula) so a track up the spine of Florida, somewhat closer to the east coast is still possible — though becoming less likely.
If the storm buzz-saws up the west coast, then Key West, Naples, Fort Myers, Tampa and Tallahassee would face severe effects — and this scenario has become most likely. If it runs up the spine of the peninsula, the storm will be quicker to decay, but hurricane-force winds would reach both coasts. Least likely, if the storm tracks closer to Florida's east coast, then Miami, Fort Lauderdale, West Palm Beach, Melbourne, Daytona Beach and Jacksonville will take devastating hits.
When Irma makes its closest approach to Florida — some time Sunday — the Hurricane Center predicts that it will produce Category 4 winds. Here is its description of the kind of damage Category 4 winds would inflict:
Catastrophic damage will occur: Well-built framed homes can sustain severe damage with loss of most of the roof structure and/or some exterior walls. Most trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas. Power outages will last weeks to possibly months. Most of the area will be uninhabitable for weeks or months.
Note that such extreme winds are typically confined to the eye wall, which is only about 10 to 15 miles wide. That is why the exact track is important in terms of where the most severe wind damage concentrates.
It's important to note that wind speeds will increase with altitude, so high-rise buildings will be exposed to even stronger winds, up to a hurricane category stronger on the upper floors.
Due to the likelihood of widespread damaging winds, one model run by researchers at several universities projects that more than 2.5 million customers in Florida and the Southeastern United States will lose power.
"Peak power outages for Hurricane Harvey were between 300,000 and 400,000, so this is many times larger than that," said Seth Guikema, a researcher at the University of Michigan leading this modeling effort
Regardless of exactly where Irma tracks, many coastal population centers in Florida will experience a devastating storm surge of 6 to 12 feet above normally dry land, inundating roads, homes and businesses. The most severe storm surge will focus immediately north-northeast of where the storm center crosses land — which could be near the southwest tip of Florida and then along Florida's west coast, including Marco Island, Naples, Cape Coral, Fort Myers, Port Charlotte, Sarasota, and up to Tampa, perhaps.
The Hurricane Center predicts all of the Florida Keys to see a storm surge of 5 to 10 feet. "It's not clear that it's a survivable situation for anybody that is still there in the Keys," said Ed Rappaport, acting director of the National Hurricane Center in a television interview.
Over the Florida peninsula, 8 to 20 inches of rain is forecast, with the heaviest amounts most likely in the south. Flash flooding is likely to occur.
Potential effects on Georgia and the Southeast
Beyond Florida, there is the likelihood for damaging winds, flooding rain and a coastal storm surge farther north. Georgia is likely to see some of the worst effects Sunday night into Monday.
Irrespective of Irma's track its circulation is enormous so it would still likely push a significant storm surge toward the Georgia and South Carolina coasts.
Tropical-storm and even hurricane-force winds are also likely to affect much of Georgia and downed trees and power outages could be a big problem there. Strong winds could expand into southern South Carolina and eastern Alabama as Monday wears on.
Heavy rains are also likely to swell north and west into Alabama, Tennessee, and western North Carolina Monday into Tuesday.
"All areas seeing heavy rainfall from Irma will experience a risk of flooding and flash flooding," the Hurricane Center said.
Irma's path so far
On Friday, before making landfall along Cuba's north central coast, Irma passed north of Haiti and then between Cuba's northeast coast and the Central Bahamas.
Thursday evening, the center of the storm passed very close to the Turks and Caicos, producing potentially catastrophic Category 5 winds. The storm surge was of particular concern, as the water had the potential to rise 16 to 20 feet above normally dry land in coastal sections north of the storm center, causing extreme inundation.
A devastating storm surge and destructive winds had also likely battered the southeastern Bahamas, near Great Inagua Island.
Through early Thursday, the storm had battered islands from Puerto Rico to the northern Lesser Antilles.
While the center of Irma passed just north of Puerto Rico late Wednesday, a wind gust of 63 mph was clocked in San Juan early Wednesday evening, and more than 900,000 people were reported to be without power. In Culebra, Puerto Rico, a small island 17 miles east of the mainland, a wind gust registered 111 mph in the afternoon.
Wednesday afternoon, the storm's eye had moved over Virgin Gorda in the British Virgin Islands, and its southern eye wall (the region of most powerful winds) raked St. Thomas in the U.S. Virgin Islands.
Early Wednesday afternoon, a wind gust to 131 mph was clocked on Buck Island and 87 mph on St. Thomas in the U.S. Virgin Islands.
Tuesday night and Wednesday morning, the hurricane passed directly over Barbuda and St. Martin in the northern Leeward Islands, the strongest hurricane ever recorded in that region and tied with the 1935 Florida Keys hurricane as the strongest Atlantic storm to strike land.
As Barbuda took a direct hit, the weather station there clocked a wind gust to 155 mph before it went offline.
The storm also passed directly over Anguilla and St. Martin early Wednesday, causing severe damage.
Irma's place in history
Irma's peak intensity (185 mph) ranks among the strongest in recorded history, exceeding the likes of Katrina, Andrew and Camille — whose winds peaked at 175 mph.
Among the most intense storms on record, it trails only Hurricane Allen in 1980, which had winds of 190 mph. It is tied for second-most intense with Hurricane Wilma in 2005, Hurricane Gilbert in 1988 and the 1935 Florida Keys hurricane.
The storm maintained maximum wind speeds of at least 180 mph for 37 hours, longer than any storm on Earth on record, passing Super Typhoon Haiyan, the previous record-holder (24 hours).
Late Tuesday, its pressure dropped to 914 millibars (the lower the pressure, the stronger the storm), ranking as the lowest of any storm on record outside the Caribbean and Gulf of Mexico in the Atlantic basin.
The storm has generated the most "accumulated cyclone energy," a measure of a storm's duration and intensity, of any hurricane on record.
Without a doubt, the World Meteorological Organization will retire the names Harvey and Irma after this season. While there have been several instances of consecutive storm names getting retired (Rita and Stan 2005, Ivan and Jeanne 2004, Isabel and Juan 2003, Luis and Marilyn 1995), the United States has been hit by more than one Category 4+ hurricane in a season only one time: 1915. Two Category 4 hurricanes hit in Texas and Louisiana six weeks apart that year.
Capital Weather Gang hurricane expert Brian McNoldy contributed to this report. Credit to tropical-weather expert and occasional Capital Weather Gang contributor Phil Klotzbach for some of the statistics in this section.