Harvey forecast to slam Texas coast as major hurricane with ‘devastating’ flood potential – Washington Post
(This article, originally published at 11:05 a.m., is regularly updated to reflect the latest information and forecast.)
Harvey rapidly intensified Thursday morning in the central Gulf of Mexico, and it officially became a hurricane early in the afternoon. The extremely dangerous storm is predicted to strengthen and plow into southeast Texas on Friday as the first major hurricane, rated Category 3 or higher (on the 1-5 Saffir-Simpson intensity scale), to strike U.S. soil in 12 years.
An incredible amount of rain, 15 to 25 inches with isolated amounts of up to 35 inches, is predicted along the middle and upper Texas coast, because the storm is expected to stall and unload torrents for four to six straight days. The National Hurricane Center said it expects “devastating and life-threatening” flash flooding.
Marshall Shepherd, a past-president of the American Meteorological Society, tweeted that he feared an “epic flood catastrophe.”
GFS model storm projection Friday night through Wednesday night. (PivotalWeather.com)
Not only are the rain and flooding concerns huge, but the storm also has the potential to generate destructive winds and a devastating storm surge — or raise the water as much as 6 to 12 feet above normally dry land at the coast.
“In all these years, it’s rare that I’ve seen a hurricane threat that concerns me as much as this one does,” said Rick Knabb, hurricane expert at The Weather Channel and formerly the director of the National Hurricane Center.
Because Harvey is positioned over extremely warm waters, the National Hurricane Center predicts that the storm, which was a tropical depression on Wednesday, will intensify further and make landfall as a Category 3 storm with 125 mph winds Friday night or early Saturday.
In anticipation of the storm, Texas Gov. Greg Abbott (R) declared a state of emergency in 30 counties. The city of Corpus Christi began “strongly encouraging evacuation” in low lying areas early Thursday afternoon.
Weather.com reported the following additional evacuation orders: “Officials in Calhoun, San Patricio and Refugio counties north of Corpus Christi issued orders on Thursday, along with the cities of Portland, Rockport, Port Aransas, Aransas Pass, Ingleside and Robstown. All residents of Brazoria County living on the Gulf side of the Intracoastal Canal have been ordered to evacuate, as well.”
At 11 p.m. Thursday, Hurricane Harvey had 85 mph peak winds and was centered about 250 miles southeast of Corpus Christi. It is tracking toward the north-northwest at 10 mph.
Hurricane, storm surge and flood warnings plastered coastal and inland portions of East Texas on Thursday evening, and tropical-storm-force winds are forecast to reach the Texas coastline by Friday afternoon.
(National Hurricane Center)
The general computer model consensus is that Harvey will make landfall Friday night or Saturday morning between Port Mansfield and Sargent, Texas, southwest of Galveston, the zone under a hurricane warning. The biggest population center in this area is Corpus Christi — which may end up very close to the landfall location.
The five-day “cone of uncertainty,” an illustration of where the storm may track, is squashed down to a circle, indicating that after coming ashore, the storm may stall, unleashing its wrath over the same general area through at least Monday or Tuesday.
(National Hurricane Center)
The rain and wind from the storm could have profound effects on oil refineries near its path.
The rain forecasts are ominous. “Somebody is going to get a rainstorm to tell their grandkids about,” said Bill Read, a former director of the National Hurricane Center.
Areas along the middle and upper Texas coast may see 15 to 25 inches of rain, with a few areas receiving as much as 35 inches, although it is impossible to pinpoint exactly where the heaviest rain will fall.
So much rain is predicted that the National Weather Service had to add a new high-end category to its forecast map, illustrating the potential for more than 20 inches:
Seven-day cumulative rainfall forecast. (National Weather Service)
Houston, the nation’s fourth-largest city, could receive 10 to 20 inches or more of rain from the storm, depending on exactly where it tracks — with the heaviest moving in Saturday or Sunday and then continuing into early next week. Matt Lanza, a meteorologist based in Houston, said 20 inches would be “devastating” for the city, depending where it fell. A worst-case scenario, Lanza said, would be for this amount of rain to fall just northwest of downtown as “all that water has to push through the bayou networks across the city into Galveston Bay.”
GFS model rainfall forecast through Thursday morning. (PivotalWeather.com)
The Weather Channel’s Knabb pointed out 9 out of 10 people who die in landfalling tropical systems in the U.S. die in water, from either flooding from heavy rain or storm surge.
“Promise yourself that you’re not going to drive your car over a water-covered roadway or drive your car around a barricade when the road is closed,” Knabb said. “Most people who die in inland flooding die in their cars”
Especially late this weekend and into early next week, areas of western and southern Louisiana could also be hit with double-digit rainfall totals.
The Hurricane Center predicts 6 to 12 feet of water — above normally dry land — inundating coastal areas immediately to the east and north of the landfall location. That amount is based on the assumption that Harvey makes landfall as a Category 3 hurricane. But the surge could be even higher (or lower) if the storm is stronger (or weaker) and will be adjusted as the forecast evolves. It is critical that affected residents heed evacuation orders.
— Greg Diamond (@gdimeweather) August 24, 2017
Keep in mind that the timing of normal astronomical tides is a factor. If the highest storm surge arrives at or near high tide, the total “storm tide” will be maximized. As the timing of landfall is pinned down, forecasts of the storm tide timing and depth will be improved, as well.
The official forecast is that Harvey will produce maximum sustained winds of 125 mph when it comes ashore, strong enough to cause widespread power outages and significant damage to homes and businesses.
At 11 p.m. Thursday, tropical-storm-force winds expanded 105 miles away from the storm center, while hurricane-force-winds were confined within 25 miles of the center. However, as the storm is likely to strengthen prior to landfall, the area affected by these strong to violent winds should expand.
A projection from modelers at several universities indicates the potential for approximately 570,000 outages in affected areas.
The storm’s intensity is unfortunately a wild card at this point. The storm rapidly intensified through the first half of Thursday before leveling off for a time during the afternoon and evening. With absolutely ideal environmental conditions, including very warm water and favorable atmospheric winds, Harvey is predicted to resume intensification Friday and to make landfall as a Category 3 hurricane with 125 mph winds. However, predicting short-term changes in hurricane intensity is extremely challenging for forecasters, so it is quite possible Harvey’s ultimate strength differs somewhat from this projections.
In addition to the uncertainty in the storm intensity and wind speeds, which has implications for how big the storm surge is, the other important uncertainties are the storm’specific track and exactly how long it will linger in Texas. Both of these factors have significant implications for where the heaviest rain falls and how long the deluge persists.
Right now, it is important for Texans in the path of this storm to understand — irrespective of where the storm makes landfall — Harvey’s footprint will be enormous because of the large expanse of its heavy rain field and long duration. Preparations be brought to completion hastily.
A note about what is considered a major hurricane
A major hurricane is technically defined as one rated Category 3 or higher on the 1-5 Saffir-Simpson intensity scale. The last major hurricane to make landfall on the United States was Wilma in October 2005. While Hurricane Ike in 2008 produced a devastating storm surge around Galveston and a massive economic toll, it was rated a high-end Category 2 storm at landfall. Superstorm Sandy, another devastating weather event, was no longer officially considered a hurricane when it made landfall near Atlantic City in 2012. It had transitioned into a what was called a “post tropical storm” as it was beginning to lose tropical characteristics.
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