(This post, originally published Saturday, was last updated Sunday morning. The latest update reflects the 10 a.m. Sunday National Hurricane Center advisory and current conditions in the Keys and South Florida.)
Large and extremely powerful Hurricane Irma is battering Florida, having slammed into the Keys with wind gusts well over 100 mph. The storm, which strengthened to a Category 4 early Sunday, is likely to rank among the worst hurricanes in the state's history.
The vicious storm is next set to hit Florida's west coast hardest, with a combination of destructive winds and a devastating storm surge. Winds in excess of 100 mph could batter numerous population centers along Florida's west coast, including Naples and Fort Myers and up the coast to Tampa. And coastal waters could rise 10 to 15 feet above normally dry land, completely inundating homes, businesses, and roads.
"The Keys through Tampa will likely experience the worst storm surge event that area has seen in generations," said Bill Read, a former director of the National Hurricane Center.
At 10 a.m. Sunday, the eye of Irma was starting to pull away from the Florida Keys, centered 25 miles northeast of Key West. The storm, packing peak winds of 130 mph, was crawling to the north-northwest at 8 mph. It was predicted to move up the west coast of Florida through the day Sunday and into Sunday night.
The storm officially made landfall at Cudjoe Key at 9:10 a.m. and, following Hurricane Harvey's assault in Texas, marked the first time on record two Category 4 storms had made landfall in the U.S. in the same year.
Winds over the Keys raged Sunday morning, gusting over 90 mph in Key West and up to 120 mph in Big Pine Key. An extreme wind warning was issued for the Lower Keys, including Key West, through 9:15 a.m., for "extremely dangerous and life-threatening" wind gusts.
Eyewitness video showed the rising storm surge flooding Key West streets:
Spiral bands were also unleashing tropical-storm-force winds in southeast Florida. Sustained winds in Miami and Fort Lauderdale were 40 to 50 mph Sunday morning, gusting to 60 to 70 mph.
The National Weather Service in Miami warned gusts could reach 100 mph at the upper floors of high rise buildings, and an isolated gust hit 100 mph at the University of Miami, according to The Weather Channel. Nearly 1.1 million customers were without power, mostly in Miami-Dade, Broward and Palm Beach counties.
Video from NBC News showed water pouring through Miami city streets, in between high rises.
As the storm's spiral bands walloped South and Central Florida, the potential for tornadoes arose in the swirling air and the Weather Service issued watches and warnings. Eyewitnesses captured photographs of a twister moving off the ocean toward Fort Lauderdale on Saturday evening.
"In the FLORIDA KEYS, it is a full-scale hurricane emergency," Bryan Norcross, The Weather Channel's hurricane specialist, posted to Facebook. "Key West is probably going to get its worst storm in modern history, and perhaps ever."
He added: "In SOUTHWEST FLORIDA – the NAPLES-FT. MYERS-CAPE CORAL area, the potential exists for the worst hurricane in history."
Hurricane warnings cover all of Florida except the western panhandle, where a tropical storm warning was in effect. Tropical storm warnings also spread over almost all over Georgia, including Atlanta, eastern Alabama, and the southern South Carolina coast.
A storm-surge warning was also issued for much of the Florida peninsula (except for a small section from North Miami Beach to Jupiter Inlet), and even extended up the Georgia coast into southern South Carolina. 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, where it said the surge is expected to be "catastrophic."
Because of the shift in the most likely storm track to the west, Miami and Southeast Florida were most likely to miss the storm's intensely destructive core, known as the eyewall, where winds are strongest. Even so, because of Irma's enormous size, the entire Florida peninsula and even the panhandle were likely to witness damaging winds. The National Hurricane Center warned the storm would bring "life-threatening wind impacts to much of the state."
A computer model projection showed nearly 2 million power outages were possible in Florida and the Southeast U.S. from the storm's winds.
While Irma's peak winds had lessened some on Saturday, easing down to 120 miles per hour, as its center scraped over Cuba's north coast, it restrengthened over the extremely warm water of the Florida straits (nearly 90 degrees).
In South Florida, conditions will continue to deteriorate Sunday as Irma chugs up the coast.
The storm will cross the Florida Keys (near Marathon) on Sunday morning, before moving up the west coast Sunday afternoon and evening, battering Marco Island, Naples, Cape Coral, Fort Myers, Port Charlotte, Sarasota and Tampa.
The storm track could still shift slightly west. If it shifts west, the center could stay over the Gulf of Mexico until hitting northern portion of Florida's Gulf Coast Sunday night, perhaps in the Big Bend area south of Tallahassee.
Models run Saturday night suggested a landfall between Naples and Tampa on Sunday afternoon or evening was plausible, but pinpointing the exact landfall location is difficult for a storm predicted to parallel a long coastline.
Effects on Florida
Here's a guide to what is most likely and where…
Time frame for worst conditions: Through Sunday evening
Biggest impact threat: Storm surge and destructive winds
The Keys are poised to take a direct and devastating hit from Irma. Winds will be on the increase into Sunday morning, with sustained hurricane-force winds expected. Catastrophic storm surge levels of 10 feet or more could inundate the entire area in a manner similar to the destruction caused by Hurricane Donna in 1960, which devastated the Keys. As a result of the extreme danger that Irma poses to the area, the National Weather Service office in Key West issued some of the strongest language you will ever see from a weather warning, tweeting: ***THIS IS AS REAL AS IT GETS*** ***NOWHERE IN THE FLORIDA KEYS WILL BE SAFE***
Southwest Florida to Tampa Bay
Time frame for worst conditions: Sunday
Biggest impact threat: Storm surge and wind
Each shift in Irma's track has spelled more bad news for southwest Florida. The Tampa Bay area hasn't had a direct hit from a hurricane since 1921, but this part of the state is home to some of the most vulnerable real estate to flooding.
The current forecast track has Irma making her final landfall in between Naples and St. Petersburg. Given the current forecast, sustained tropical-storm-force winds are expected Sunday morning, with winds gradually increasing. The Naples area may well be hit the by the strongest winds, with sustained hurricane force winds of 100 to 125 mph with higher gusts moving in by Sunday midday or afternoon.
Storm surge will be an especially large concern, with upward of 10 to 15 feet of surge possible as the center of Irma passes by. "This is fast moving, destructive water," the Weather Channel's Norcross said. "You cannot drive through it and you cannot stand in it. It will sweep buildings away. Storm surge is the deadliest hazard in a hurricane."
Miami/Fort Lauderdale/Dade County
Time frame for worst conditions: Through Sunday evening
Biggest impact threat: Heavy rain and strong winds
Despite the continued shift westward in Irma's forecast track, the Miami area is by no means off the hook. Sustained tropical-force winds will continue coming in waves throughout the day as spiral bands cycle in, with hurricane-force wind gusts embedded in some of the stronger rainbands. The worst conditions will persist through much of the day Sunday, with sustained winds of 60-plus mph with gusts in excess of 75 mph. Rainfall totals will range from 8 to 15 inches, with the bulk of the rain coming in bursts where rainfall rates could reach four inches per hour.
While still a concern, storm surge will not be as serious here as in other parts of the state due to a combination of a lesser rise in water (3 to 6 feet) and deeper offshore waters.
Time frame for worst conditions: Sunday morning through Monday morning
Biggest impact threat: Heavy rain/strong winds
Inland areas will not be immune to impacts from Irma. As it has been noted, Irma is an extremely large storm, with hurricane force winds extending some 90 miles from the center. As the storm begins to interact with more land, it will lose some of its peak wind speeds but actually grow in physical size. Sustained tropical-force winds will begin striking Orlando and central Florida by Saturday afternoon, with hurricane-force wind gusts possible late Sunday night.
The somewhat forgotten danger with landfalling hurricanes in the extreme rainfall that can develop over inland areas. Flooding will certainly be a concern as rainfall totals are expected to be in the range of 8 to 18 inches by Monday.
Potential effects on Georgia and the southeastern U.S.
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, where a storm surge warning is in effect.
Tropical-storm and even hurricane-force winds are also likely to affect much of Georgia, with 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
Just after 9 p.m. Friday, Irma made landfall on the north coast of Cuba as a Category 5 hurricane, with maximum sustained winds of 160 mph. It became that country's first Category 5 hurricane since 1924. Fueled by the extremely warm ocean temperatures, Irma reintensified to the maximum hurricane classification level after weakening slightly on Friday afternoon.
As it scraped Cuba's north coast early Saturday, it produced a sustained wind gust of 118 mph, and a gust to 159 mph reported at Falla, Cuba in the eyewall of hurricane.
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 main island, 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 eyewall 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.
Irma's landfall pressure of 929 millibars in the Florida Keys was the lowest for any U.S. landfalling hurricane since Katrina (920 millibars) and for a Fla. landfall since Andrew (922 millibars). It ranks as the 7th lowest pressure of any U.S. landfalling storm.
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.