Dorian isn’t moving because the upper atmosphere is too calm

“This is unprecedented,” said Jeff Masters, meteorology director at Weather Underground who used to fly into hurricanes. “We’ve never had a Category 5 stall for so long in the Atlantic hurricane record.”

What’s happening — or more aptly, not happening — has been an ongoing battle between high pressure systems that push storms and low pressure systems that pull them.

A high pressure system in Bermuda has been acting like a wall, keeping Dorian from heading north. But a low pressure trough moving east from the Midwest has eroded that high and is trying to pull Dorian north. Those two weather systems “are fighting it out and neither is winning,” Masters said.

There’s just no flow pushing it anywhere. Think of it like a tiny paper boat or a pebble in a stagnant pond, which just doesn’t move, said Colorado State University hurricane researcher Phil Klotzbach.

Air — high off the ground and closer to where people live — is often stagnant in the summer and this is an extreme version of that, Masters said.

In 2017, Hurricane Harvey got stuck when steering currents collapsed, absolutely drenching Houston, but that wasn’t as powerful a storm as Dorian, Klotzbach said.

Usually hurricanes that don’t move eventually kill themselves because they churn up colder water from deep below the surface and storms need warm water as fuel, Masters said.

“It’s got to keep moving,” Masters said.

But the Bahamas and the Gulf Stream are one of the few places where warm water runs so deep. Stalling isn’t as much of a death sentence there as elsewhere, but it will still weaken the storm a bit, which is good for Florida and the U.S. East Coast, Klotzbach said.

And the longer Dorian stalls in the Bahamas, the more the low pressure system has a chance to erode the high pressure and pull the hurricane north and away from Florida, Masters said.

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