Zombie storm comes back from the (mostly) dead to threaten Gulf Coast with biblical flooding
It's the tropical storms you think are dead but come back to life that you need to be truly afraid of.
One such storm, Tropical Storm Harvey, is poised to pick up copious amounts of moisture from the bathtub warm waters of the Gulf of Mexico, before making a slow-speed collision with the low-lying Texas coast this weekend.
The storm is intensifying, and is expected to be a hurricane at landfall.
Like the meteorological equivalent of a White Walker from Game of Thrones, Harvey had previously been a named storm that dissipated as it crossed Mexico’s Yucatan Peninsula earlier this week.
The storm has the potential to drop colossal amounts of rain from Corpus Christi, Texas to Lafayette, Louisiana, with the flood-prone city of Houston in the middle of the threat zone.
Rainfall totals could exceed 20 or even 30 inches in some places, since the storm is expected to meander along the Texas coast once it makes landfall, moving less than 500 miles from Friday through Monday morning. 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.
Such a scenario, with a juiced up 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.
Parts of Louisiana are still recovering after record rains caused widespread damage in 2016, making this storm particularly unwelcome.
The National Weather Service is raising the alarm with its flood outlooks, warning of "life-threatening flooding" in coastal Texas and western Louisiana in particular. The agency has hoisted a hurricane warning for areas from Port Mansfield to Matagorda, Texas, including Corpus Cristi. A tropical storm warning is in effect for the Houston metro area, including Galveston, Texas.
Tropical storm force winds are expected to begin buffeting the Texas coast late Friday or 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.
As of Thursday morning, the National Hurricane Center expected Harvey to come ashore as a Category One hurricane, with maximum sustained winds of about 85 miles per hour.
Regardless of the category, which depends on the storm's winds, the real threat from Harvey, will be water, both at the coast with storm surge flooding, as well as inland, with heavy — potentially epic —rains.
Storm surge warnings are in effect along the Texas coast, from Port Mansfield to San Luis Pass, Texas. In this area, 5 to 7 feet of flooding above ground level can be expected if the storm hits at the time of high tide.
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 anomalous, if not historic, rainfall event.
Hurricanes and tropical storms are weather systems of extraordinary ferocity, but they are fickle when it comes to the path they travel.
Upper level winds steer these weather systems, and that may prove to be Texas’ Achilles heel when it comes to flood vulnerability from Harvey. Two areas of high pressure, one to the east of the storm and another to the west, may pin it in place once the storm crosses the coast.
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.
There are still many uncertainties involved in the forecast for Harvey, particularly concerning its rate and degree of intensification, which will have an impact on its path. Computer models may not have a firm grip on its likely track since it is still a relatively diffuse storm system, lacking a compact core.
The National Hurricane Center is dispatching aircraft to fly in and around the storm to gather data that will then be fed into supercomputers used to help them generate forecasts.
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. Scientists expect that as human-caused global warming continues and the atmosphere holds more moisture, tropical storms and hurricanes will drop heavier rains.
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