Powerful high-pressure system steered Harvey to Texas .
Harvey could lose steering currents, become stranded.
The likely path of tropical storms
and hurricanes, pulled this way and that by atmospheric pressure both high and low, near and far, can be difficult to predict.
And indeed, earlier this week, meteorologists’ model for Hurricane Harvey showed a spaghetti tangle of potential destinations along the Gulf Coast. By Friday, though, the storm was fixed on Texas, sparking uniquely apocalyptic language from expert hurricane trackers.
“It’s going to be catastrophic,” said Troy Kimmel, who lectures on meteorology at the University of Texas and broadcasts the weather for KOKE-FM and the Austin Radio Network. “This storm will change the Texas coast, no doubt in my mind. There will be areas that will be uninhabitable for quite
some time.” As for Central Texas, Kimmel sees 1 to 3 inches of rain in the Hill Country, 4 to 8 inches in the Austin area and 8 to 15 inches in Bastrop and Caldwell counties. But he cautions that the “gradient” of rain distinctions is steep, and a slightly greater penetration of Harvey onto the plains before it stalls for three days could make a huge difference in local rainfall.
“If that were to go any farther to the west, that could get Austin in a whole lot of trouble really fast,” Kimmel said.
U.S. hurricanes have their birth in the eastern Atlantic, near Africa, and generally are driven westward by what are called trade winds. But normally there is a huge area of high pressure in the Atlantic known as the subtropic ridge, or the Bermuda High. Depending on the location of that ridge, more to the east or to the west, a storm might turn sharply right (to the north) and never visit the United States.
On the other hand, that ridge may channel storms toward the East Coast or into the Gulf of Mexico. The ones that make it to the gulf are subject to other influences, including water temperature (hotter water feeds and speeds a storm) and the prevailing and competing west-to-east winds and weather systems of North America. Those systems and the lack of ocean water weaken and generally pull gulf cyclones quickly to the north after they make landfall.
That hasn’t occurred with Harvey, and isn’t expected to, Kimmel said, primarily because of a very strong high pressure system camped over the Southwestern United States. That high had moved to the west, drawing Harvey toward Texas, and then edged back east. That trapped the storm near the Texas coast and, after an unusually long time, moved it northeast toward Houston.
“The one thing all the models agree on now is they get that system on the coast within a two-county range, and then it loses its steering currents entirely,” he said. “It kind of gets stranded somewhere near Goliad, and the damn thing just sits there.”
And with the storm’s eye that close to the warm Gulf, with the storm radiating out for 100 miles or more, the rains and flooding are expected to be epic. Thus the predictions of 30 to 35 inches in Victoria and points near there, with lesser but still large amounts over much of the eastern half of Texas in the next several days.
“That’s what is going to result in so much damage,” Kimmel said. “It is a storm that, if it verifies, is truly unique.”