During any prolonged disaster situation, rumors run rampant and social media only serves to exacerbate the situation. It can make a terribly stressful situation even worse for all of us with already frayed nerves. The latest making the rounds is the idea that current Tropical Storm Harvey — at time of posting just beginning to cross Matagorda Bay — will emerge over the warm Gulf of Mexico waters and re-form into a sizable hurricane making landfall at Galveston and tramping its way across Houston, something our friend Eric Berger over at Space City Weather referred to as the "Zombie Hurricane Harvey Scenario."
The rumored forecast spread worries across social media that round two of Harvey could be as bad as or worse than round one. As Berger put it in his post, "This is obviously a scary scenario, but frankly it’s not one we’re losing too much sleep about here."
To take that a step further, the National Hurricane Center is forecasting only slight strengthening of Harvey once it's over open water, no more than about a five- to ten-knot increase in winds, keeping it well below hurricane strength, and a landfall east of the city sometime on Wednesday morning. But even with two days over the warm waters of the Gulf (the very thing that spun up Harvey in the first place), it is unlikely Harvey will return to hurricane status for at least four reasons.
Harvey is weak.
All the time over land has taken its toll on Harvey. At the time of posting, the storm was barely a tropical storm and even the 35-knot winds were estimated for only the outermost rain bands. If this storm were over the open ocean, it might be designated as a depression given its ragged appearance and lack of inner core, which brings us to...
Harvey lacks an inner core.
One of the key characteristics of a tropical storm is a tight inner core surrounded by counterclockwise circulation. All low pressure systems rotate around a center of circulation, but in hurricanes, that rotation is ramped up (same thing in tornadoes on a micro scale). As storms strengthen and wrap moisture around that center, it grows in strength and forms this inner core surrounded by storms we commonly refer to as an eye. Harvey, at this point, resembles a comma, with a wide open side to the west and south of the center, which will dramatically slow strengthening.
Harvey is being invaded by dry air.
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The lack of a defined inner core is due mostly to the invasion of dry air from west Texas (God bless deserts!). Harvey's convection (that counterclockwise motion) has actually drawn dry air directly into the center of itself over the past 24 hours, which has caused it to weaken and has even helped to push most of the soaking rain east of Houston today. That dry air will persist, albeit to a lesser degree, with Harvey over water.
Harvey is encountering wind shear.
Wind shear, a significant detriment to the development of tropical storms, is slowing Harvey's growth thanks to an upper-level trough of low pressure over the state. Those high-altitude winds dramatically inhibit any storm's ability to strengthen and the shear produced by this trough, while moderate, will do the same to Harvey.
Bottom line, Harvey has caused an unprecedented disaster in our entire region, but there is reason to hope — good, scientific reason — that the worst will soon be behind us. Once we are in the clear, we can move on to the long, slow process of recovery and worry about the only zombies that matter, the ones on Game of Thrones.