WASHINGTON (AP) -- Hurricane Harvey is shaping up as just about a worst-case scenario storm with possible flooding from two different directions.
Harvey intensified rapidly because it's been meandering over deep warm water and has calm air at 40,000 feet (12,192 meters) high. It's moving slowly and will be stuck over the Texas coast through the middle of next week, which means rainfall measured in feet, not inches.
Put them all together and you've got a potential disaster that really has the National Hurricane Center grasping for ever scarier words like "life-threatening" and "catastrophic," ''dangerous" and "grave risk."
"The Houston area and Corpus Christi are going to be a mess for a long time," said University of Miami senior hurricane researcher Brian McNoldy, who said this could be as big an economic threat as 2005's Katrina.
"I can't remember a storm that made landfall that was both very strong and very slow and not really even moving inland and it stalls along the coast," McNoldy said.
To top off all that, the hurricane center forecast over the next five days --- and that often gets changed --- is for Harvey to hug the coast and stay strong enough to be a tropical storm through Wednesday at least. Sometime early next week it is forecast to go back into the warm Gulf of Mexico waters, which provides fuel, then turn back in for a potential second hit on what may be an already flooded Houston-Galveston area.
During this meandering time, the storm will likely dump 2 feet (0.61 meters) to 3 feet (0.91 meters) of rain, often on areas that don't handle much smaller rainfall amounts well.
It sets up a nightmarish and unprecedented situation, meteorologists said.
The heavy rain is likely to cause massive inland flooding --- water that's trying head out to the sea. But coming from the other direction may be 4 feet (1.22 meters) to 5 feet (1.52 meters) of storm surge --- extreme rise of water above normal tide that just stays there. Those two flooding events are likely to come crashing into each other like a train and a car, said Galveston-based storm surge expert Hal Needham of the private firm Marine Weather and Climate.
"Essentially there's absolutely nowhere for the water to go," Needham said. Galveston Bay, where rain normally escapes to, will already be elevated. It's "becoming more and more likely that something really bad is going to happen," he said.
Earlier Friday, Harvey reformed and widened its eyewall, meaning its likely storm surge will be stronger, said MIT meteorology professor and hurricane expert Kerry Emanuel
Grasping for anything that doesn't look dreadful, Emanuel said at least there's a chance that the worst of Harvey's winds --- to the north and east of the eye --- could first hit a sparsely populated barrier island between Corpus Christi and Houston.
Here are some ingredients that make Harvey so dangerous:
Warm water is the fuel for hurricanes. Harvey has been feeding over "abnormally" warm and deep water in the Gulf of Mexico, said National Weather Service director Louis Uccellini.
If winds at 40,000 feet (12,192 meters) high are strong in the wrong direction it can decapitate a hurricane. Strong winds high up remove the heat and moisture that hurricanes need near their center and also distort the shape. But Harvey doesn't have to fight those winds.
Harvey is forecast to stay at tropical storm strength over the same general area through Wednesday at least. While it's there, it will pour. And it may be close enough to get more moisture from Gulf of Mexico and keep the downpours going, meteorologists said.
"The fact that this storm is going to linger is going to lend itself to the catastrophic nature of this storm," Uccellini said.