Hurricane Harvey is rapidly intensifying over the bathtub-warm waters of the Gulf of Mexico, rocketing from a tropical depression to an 85-mile-per-hour hurricane in less than 24 hours, with more intensification to come. As of Friday afternoon, it had reached Category 3 intensity.

The storm presents south and southeastern Texas with nothing short of a worst-case scenario.

Hurricane Harvey is forecast to roar ashore along the middle Texas coast with maximum sustained winds of 125 miles per hour or greater, making it a high-end Category 3 storm, on Friday night or Saturday morning. It's even possible it could hit as a low-end Category 4 storm, capable of causing widespread destruction.

If it hits land at such a high intensity, Harvey would be the strongest hurricane to hit the U.S. in 12 years, since Hurricane Wilma struck Florida in 2005.

The storm is straight out of central casting. It's as if a meteorologist were asked to simulate a storm that would challenge citizens and emergency managers to the maximum degree, and then that storm were accidentally unleashed into the real world.

Radar scan from "Kermit" (NOAA P-3 recon) about an hour ago, inside hurricane #Harvey. pic.twitter.com/02y7CYIU1E — Greg Postel (@GregPostel) August 24, 2017

The rapidly intensifying storm is lumbering toward the coast, and once it makes landfall Friday night or Saturday morning, it's forecast to sit in place for days, resulting in potentially catastrophic rainfall amounts across a broad area. Some spots could see upwards of 40 inches of rain between Friday and Wednesday, with areas including Corpus Christi and Houston in the path of heavy rainfall.

In addition, the storm will bring storm surge flooding to the coast, with as much as 12 feet of inundation above ground level expected in some spots — possibly more if the storm intensifies further.

Satellite loop showing Hurricane Harvey intensifying rapidly in the Gulf of Mexico on Aug. 24, 2017. Image: rammb/cira/colorado state university

Because the storm is likely to get trapped over South Texas for days, caught between two high pressure systems — one to the east, and the other to the west — it's also likely that inland flooding will be compounded by the strong onshore winds, which will discourage the floodwaters from draining into the sea.

Some computer models even loop the storm back out over the Gulf of Mexico, only to make a second landfall in northeastern Texas or western Louisiana early next week.

Even the most sober-minded meteorologists have been reaching for superlatives on Thursday to try to warn Texans that what they are facing is no ordinary tropical weather system.

“Any time you have a Category 3 storm, it is a threat. Now add in the fact that it may sit in some form for almost a week dumping rain, you have a huge problem,” said Marshall Shepherd, a professor of meteorology at the University of Georgia, in an email.

Shepherd tweeted on Thursday morning that he feared an “epic flood catastrophe” from Harvey.

Here's the problem with #Harvey. Massive western ridge keeps it from moving inland much. Trough too far away in the east to grab it. Stalls pic.twitter.com/O3xO5YC7zc — Eric Fisher (@ericfisher) August 24, 2017

This 12z ECMWF run has no less than FOUR DAYS of hurricane conditions along the TX Gulf Coast.

Easy to say, worst case scenario. pic.twitter.com/OqIZZKdgsf — Sam Lillo (@splillo) August 24, 2017

Such a scenario, with a water-laden hurricane making landfall and stalling out, is the stuff of nightmares for flood forecasters, since the number one killer from tropical cyclones is inland flooding. Though most people think of wind as a hurricane's greatest weapon, flooding kills nine out of 10 people who perish in such storms.

The National Weather Service is not mincing words about the threat posed by this storm, either.

The Weather Service in Houston and Galveston is warning residents to "prepare for life-threatening rainfall flooding." A local statement put out by the office warns that "Small streams, creeks, canals, and ditches may become dangerous rivers. Flood control systems and barriers may become stressed."

While individual computer model projections should not be taken literally, some models are showing up to 50 inches of rain from this storm across parts of southeastern Texas as the storm meanders for days. What this tells forecasters is that the potential is there for an historic rainfall event.

For the area likely to see the strongest winds of greater than 100 miles per hour, the agency is putting out the following message (emphasis added):

Potential impacts in this area include: Structural damage to sturdy buildings, some with complete roof and wall failures. Complete destruction of mobile homes. Damage greatly accentuated by large airborne projectiles. Locations may be uninhabitable for weeks or months.

For coastal areas, the agency is saying there will be a "life-threatening [storm] surge having possible devastating impacts."

Storm surge flooding occurs when a storm piles water toward the coast, from a combination of strong onshore winds and low atmospheric pressure. Sea level rise from human-caused global warming as well as gradual sinking of some coastal land areas can exacerbate storm surge flooding.

Throughout the day on Thursday and into Friday, the storm surge flood forecast has grown for the middle Texas coast. From the north entrance of Padre Island National Seashore to Sargent, the National Hurricane Center is predicting between 6 and 12 feet of flooding above ground level if the storm hits at the time of high tide. Between Sargent and Jamaica Beach, the surge would be slightly lower, at 5 to 8 feet above ground level.

Storm surge warnings (dark purple) and watches (light purple) for the Texas coast. Image: noaa/nhc

Because the storm will hit the coast and then stall, storm surge flooding could occur during multiple high tide cycles, subjecting the coast to battering waves that will exacerbate the damage.

Here is what the Weather Service forecast office in Houston/Galveston communicated on Friday morning, regarding the storm surge threat (emphasis added):

Widespread deep inundation, with storm surge flooding greatly accentuated by powerful battering waves. Structural damage to buildings, with many washing away. Damage greatly compounded from considerable floating debris. Locations may be uninhabitable for an extended period.

On the storm's current path, researchers project as many as 300,000 customers could be without power from high winds, with upwards of 1.25 million customers without power if the storm track shifts to the north.

Rainfall outlook issued Friday evening, Aug. 24, 2017, showing a large area of 20 to 35-inch rains along the Texas coast. Image: noaa/nhc

"Harvey poses a uniquely dangerous threat to Texas. Any one of its possibilities would be a serious risk by itself — extreme rainfall over a large area, widespread flooding, devastating storm surge, major power outages, prolonged impacts," Bob Henson, a meteorologist for Weather Underground, said via email.

"When you combine all of the threats posed by Harvey, it's hard to overstate what a potentially disastrous setup this is for millions of Texans."

Parts of Louisiana are still recovering after record rains caused widespread damage in 2016, making this storm particularly unwelcome.

Tropical storm force winds are expected to begin buffeting the Texas coast during the day on Friday with hurricane force winds crossing the coast on Friday night, and some places could see high winds pushing the waters of the Gulf of Mexico onshore for days, resulting in storm surge flooding over many high tide cycles.

Rainfall forecast showing incredible totals over southeastern Texas during the next several days, as of Aug. 24, 2017. Image: weather prediction center/weatherbell analytics

Texas has an ominous past when it comes to dealing with slow-moving tropical storms. Tropical Storm Allison, which struck the Houston area in June of 2001, killed 41 people, and caused $9 billion in damage. Harris County alone had $5 billion in damage along with 22 deaths from that storm.

Since then, heavy rainstorms have continued to demonstrate Houston's vulnerability to heavy rains. A flood event in April 2016 virtually shut down the third largest city in the U.S. by flooding highways, parking lots, and overwhelming drainage systems.

Because it is rapidly intensifying, it's possible that its ferocity will catch many Texans, as well as officials in Washington, off guard. The center of Harvey is moving over Gulf waters that are 1 to 2 degrees Celsius, or 1.8 to 3.6 degrees Fahrenheit, above average for this time of year, adding more fuel to power the hurricane.

Typically, before such major storms the federal government pre-positions relief supplies closer to the area slated to be hit, but this storm was barely a tropical storm as of Thursday morning, making such moves unnecessary at that time. Now, it could be too late.

The Trump administration has appointed a head of FEMA, but the National Oceanic and Atmospheric Administration (NOAA), which is responsible for forecasting the storm, is operating with an acting director. So, too, is the National Hurricane Center in Miami, which is part of NOAA. In addition, the Department of Homeland Security, which includes FEMA, Coast Guard and other responding agencies, has an acting director since Trump tapped former secretary John Kelly to be his chief of staff in late July.

There are still uncertainties involved in the forecast for Harvey, particularly concerning its continued rate of intensification and exact track. Pinpointing where the heaviest rain will fall is also a challenge at this point.

Across much of the U.S. and around the world, extreme rainfall events are becoming more common as the world warms and the atmosphere holds more moisture. In addition, scientists expect that as human-caused global warming continues and the atmosphere holds more moisture, tropical storms and hurricanes will produce heavier rains.

Aug. 25, 2017: This story has been updated to include the latest forecast information.