'We've Never Forecast This Much Before': Hurricane Harvey's Ominous Forecast and How Meteorologists Reacted a Year Ago

"Harvey was the most significant tropical cyclone rainfall event in United States history, both in scope and peak rainfall amounts, since reliable rainfall records began around the 1880s," meteorologists Eric Blake and David Zelinsky wrote in the National Hurricane Center's final report on Harvey.

(MORE: Full Hurricane Harvey Recap)

Coupled with the pummeling from the Category 4 landfall along the Texas coast, Harvey was reponsible for $125 billion damage in the U.S., according to an estimate from NOAA, making it second only to Katrina in the list of costliest U.S. hurricanes, when adjusting for inflation.

The forecast in the days leading up to Harvey challenged even the most experienced meteorologists to communicate the magnitude of the danger and put into context.

As the events unfolded, some meteorologists felt sick to their stomachs, even helpless, as feet of rain produced record flooding.

What follows is a daily diary of reactions from meteorologists before Harvey had redeveloped in the Gulf of Mexico through the end of the heaviest rain in Texas and Louisiana.

Aug. 21: First Signs

Harvey's remnants were still in the western Caribbean Sea, but it was becoming apparent Harvey would have a second life in the western Gulf of Mexico, after shearing out as a tropical wave two days earlier.

The first sign of a potentially major rainfall event showed up in forecast models.

Aug. 22: Heavy Rain Concern Grows

As the remnants of Harvey's first life soaked Mexico's Yucatan Peninsula, the National Hurricane Center scheduled reconnaissance missions for the following day.

Model rainfall forecasts showed an increasingly large heavy rain footprint, with higher amounts, and meteorologists became worried.

Matt Lanza, a meteorologist based in Houston and managing editor for Space City Weather, made a disconcerting analogy of the Harvey forecast to a destructive flood the previous summer.

The National Weather Service office in Corpus Christi, Texas, tested its hurricane shutters, and it was already getting busy at the NWS office in the Houston metro area. 

Aug. 23: Harvey's Back and the Forecast Slows

Harvey came back as a tropical depression, west of the Yucatan Peninsula before noon on Aug. 23.

Even more ominous was the slower forecast trend for Harvey's motion after its landfall, producing rainfall totals in averages of multiple forecast models known as ensemble means that were increasingly foreboding. 

By afternoon, given these trends, some wondered whether this would be the last time we'd use the name Harvey, since particularly destructive and/or deadly Atlantic names are retired from future use.

The Harris County Flood Control District was preparing, and disaster declarations were issued for 30 Texas counties ahead of Harvey.

Aug. 24: Forecast Going Downhill

Harvey, now a hurricane, was rapidly intensifying. By afternoon, the state's first Category 4 landfall since 1961 was at least on the table for discussion.

National Weather Service Corpus Christi meteorologist Greg Heavener was among a number of NWS meteorologists who had to board up his home and send his family inland while preparing to cover the storm.

Meanwhile, the rainfall forecast had become even more alarming.

NOAA meteorologist David Roth, who has documented rainfall from tropical cyclones dating to the 1960s, presciently tweeted that Harvey's rainfall could threaten both a Texas and U.S. tropical cyclone rainfall record. 

Because of Harvey's upcoming stall, the forecast cone was no longer cone-shaped, instead resembling a giant blob where the forecast location of Harvey's center five days out was virtually the same as its forecast two days out. 

The forecast had become so ominous, University of Georgia atmospheric scientist, Dr. Marshall Shepherd, as many others, were hoping and praying to be wrong.

Taylor Trogdon, a scientist at the National Hurricane Center, arguably had the most jarring take on the forecast.

Dr. Rick Knabb, former director of the National Hurricane Center and hurricane expert at The Weather Channel, recorded a special message, warning of the danger of Harvey.

Aug. 25: 'We've Never Forecast This Much Before'

Those were the words tweeted by NOAA meteorologist David Roth in a reply to a tweet by NHC meteorologist Eric Blake on the massive size of the Harvey rainfall forecast put out by NOAA's Weather Prediction Center.

Bob Henson, meteorologist at Weather Underground, put that extreme rain swath in perspective. When a late-morning NHC forecast had Harvey lingering near the Texas coast for five days, Henson tweeted simply, "Analogs fail."

It was hard to comprehend the volume of water from this prolific rain and the storm surge headed for the Texas coast.

Meteorologists were running out of words to describe what was coming and feared the words being used might, for a lesser impact storm, be considered overhype. 

For some meteorologists, the forecast was enough to turn their stomachs.

For meteorologists in Harvey's swath, like Harris County Flood Control District meteorologist Jeff Lindner, it was time to settle in for a long stay.

Then there was Harvey's rapid intensification. 

NWS-Corpus Christi issued a hurricane statement that morning with jarring potential impacts and a chilling quote: "Locations may be uninhabitable for an extended period."

Harvey made landfall late that night just up the coast from Corpus Christi as a Category 4 beast, ransacking that part of the Texas coast with 6 to 10 feet of water above ground level and wind gusts to 145 mph.

Aug. 26: Landfall Devastation, Rainfall Disaster Kicks In

Perhaps Dr. Marshall Shepherd summed up the feeling among meteorologists that morning: "Part of me is afraid to turn on @weatherchannel and for daylight to come...and days of rain just beginning," Shepherd tweeted.

The devastation along the Texas coast from the eyewall of Harvey was as bad as feared.

Harvey's stall began later that morning and shifted into the prolific multi-day rainfall event feared for days.

Houston ABC13 TV meteorologist Tim Heller couldn't have been more blunt regarding the communication of this threat.

Houston meteorologist Matt Lanza was hoping for a miracle.

At the Harris County Flood Control District, a retired Houston TV meteorologist was called in to help. 

That night, it quickly went downhill in America's fourth most populous city, prompting this urgent tweet from the NWS office.

Aug. 27: Worse Than Allison, in Half the Time

The night of Aug. 26 into Aug. 27 will be etched in memory of Houston area residents.

Rain rates of over 6 inches per hour turned streets and freeways into bayous, with water rising so rapidly people climbed into their attics to stay above water.

This prompted the NWS and emergency management to issue an urgent plea for those escaping rising water in their homes to instead climb to rooftops.

First responders were taking extraordinary measures to save lives in Harris County, meteorologist Jeff Lindner tweeted.

High water on all roads leading to Hobby Airport prompted a shutdown of all runways. KHOU TV was forced to evacuate due to water pouring into the station. 

The scenes were eerily reminiscent of Allison's epic flood of 2001, but there was already more rain in half the time compared to Allison.

Incredibly, there was more rain ahead. This wasn't a terrible climax, but rather one chapter.

Meteorologists even had to tweak rainfall maps as rainfall totals went beyond the upper limits of map color legends.

One small ray of light in this was the number of volunteers with boats willing to help in Harris County.

Aug. 28: As Houston Treads Water, Beaumont/Port Arthur Disaster Unfolds

As Houston and southeast Texas struggled with the massive volume of water, first responders and staff meteorologists worked tirelessly, despite their own homes being either damaged or flooded.

The devastation was taking its toll on even seasoned journalists and Houston residents, used to seeing flood events, particularly so far this century.

And the rain wasn't over.

After several rainbands already dumped over a foot of rain over Beaumont and Port Arthur, Texas, the most prolific rainfall of Harvey tipped the scales to catastrophic flooding beginning on August 28.

Rain rates of at least 5 inches per hour were estimated over the twin Upper Texas coast cities, rates that, perhaps admittedly, some meteorologists may have become numb to by this time.

Again, NHC scientist Taylor Trogdon summarized the feelings of some meteorologists watching this all unfold that evening, as more soaking rain moved back over the Houston metro area.

As if to rub salt in the wound, what would later become Hurricane Irma was just beginning to enter the picture off the African coast.

One small sign of hope that evening was the sight of a double rainbow seen over the search and rescue area in Texas, as documented by the father of meteorologist Kait Parker, a retired firecChief and Texas Task Force 1 volunteer.

Aug. 29: An Unparalleled Drenching

The rain siege on the Upper Texas cities of Beaumont and Port Arthur, Texas, and adjacent areas of Louisiana kicked into high gear, producing waves of flood water on Interstate 10 in what I consider to be one of the most iconic photos of Harvey.

As this was happening, an all-time continental U.S. rainfall record for any tropical cyclone was topped. Later, two gauges in Jefferson County, Texas, in the towns of Nederland and Groves, would measured an incredible 60 inches of total rainfall, setting an all-time U.S. tropical cyclone rain record, including Hawaii.

Even for meteorologists who are used to looking at statistics, and were expecting extreme rainfall, the totals coming out of east Texas were in a different galaxy.

In a forecast discussion, the NWS Houston metro office wrote the Harvey storm total rainfall was "simply mind-blowing that has lead to the largest flood in Houston-Galveston history."

The inability of a second system near the coast of North Carolina to develop was a small dose of relief.

The best news of all, though, was seeing rain finally end in Houston that evening.

August 30: As One Saga Ends ...

Heavy rain was still pounding areas near the Sabine River in east Texas, Louisiana, as well as other parts of the South.

After over a week of shaking our head in disbelief over the forecast, perhaps the most eye-popping statistic we saw regarding Harvey's epic rain was 4,238.

That was the percent of average rainfall Beaumont/Port Arthur, Texas, picked up from Aug. 25-30.

In other words, the 47.47 inches of rain in that six-day period was over 42 times the average rainfall in that time, over five times the previous record total for that time.

As the Harvey rain saga was wrapping up, forecast models were suggesting another area of low pressure needed our attention in the western Gulf of Mexico.

Fortunately, that system didn't develop. Finally, the hurricane season cuts everyone a break, right? Harvey would be the one big event.

Unfortunately, that same day, Irma became a tropical storm in the eastern Atlantic Ocean. It later ransacked parts of the Caribbean and Florida. Its forecast also alarmed meteorologists in the days before impact.

The catastrophic strike of Hurricane Maria in Puerto Rico, Dominica and the Virgin Islands was the exclamation point on a truly terrible 2017 hurricane season, one many meteorologists hope they never see the likes of again.