Strengthening Harvey forecast to slam Texas coast as first major hurricane in US since 2005

(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.

Because it is positioned over extremely warm waters and strengthening so fast, the National Hurricane Center predicts that the storm, which was a tropical depression on Wednesday, will make landfall as a Category 3 storm with 125 mph winds Friday night or early Saturday.

“Harvey is expected to be a major hurricane at landfall, bringing life-threatening storm surge, rainfall, and wind hazards to portions of the Texas coast,” the Hurricane Center said in its 5 p.m. discussion.

On Wednesday, Texas Gov. Greg Abbott (R) declared a state of emergency in 30 counties in anticipation of the storm. The city of Corpus Christi began “strongly encouraging evacuation” in low lying areas early Thursday afternoon.

Weather.com reported the following additional evacuations: “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 5 p.m., Hurricane Harvey had 85 mph peak winds and was centered about 305 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 morning, and tropical-storm-force winds are forecast to reach the Texas coastline Friday morning.


(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.

Texas has not been hit by a hurricane since 2008, when Ike crashed ashore near Galveston. Harvey could be a storm Texans remember for many years to come.

The rain

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.


Seven-day cumulative rainfall forecast. (NOAA/WPC)

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)

Especially late this weekend and into early next week, areas of western and southern Louisiana could also be hit with double-digit rainfall totals.

Storm surge

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.

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.


(NOAA)

Wind

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.

A projection from modelers at several universities indicates the potential for approximately 500,000 outages in affected areas.

Uncertainties

The storm’s intensity is unfortunately a wild card at this point. Rapid intensification, which has begun, is a poorly understood and poorly modeled process. But, with absolutely ideal environmental conditions, there is reasonable possibility that Harvey becomes a major hurricane by landfall Friday.

In addition to the uncertainty in the wind speeds, which has implications for how big the storm surge is, the other important uncertainties are the storm’s motion and duration, which have significant implications for where the heaviest rain falls and how long it lasts.

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 its long duration. Preparations should begin immediately.

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.

Article source: https://www.washingtonpost.com/news/capital-weather-gang/wp/2017/08/24/rapidly-strengthening-harvey-forecast-to-slam-east-texas-as-major-hurricane-and-stall/

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