• High and low pressure will buffet the storm as it moves west
  • U.S. threat hard to gauge as many forces are acting on Erika

The way hurricanes and tropical storms can be buffeted by the weather systems they encounter is increasingly important to the U.S. East Coast as Erika limps through the Caribbean.

Large weather patterns can interact with tropical systems like a pack of toddlers chasing a balloon across a living room.

Right now, the biggest toddler in the room is a high pressure system just to the north of Erika’s current position, and it’s going to have a lot to say about the path the storm takes - and even if it survives.

The winds around high-pressure systems spin clockwise in the Northern Hemisphere, so if you imagine a big wheel in the Atlantic, Erika is hitching a ride along the bottom of the wheel and heading due west.

“They like to hug the periphery of the high,” said Dan Kottlowski, a meteorologist with AccuWeather Inc. in State College, Pennsylvania.

If this system stays strong, Erika will take a more westerly path into the second-largest Caribbean island, Hispaniola, considered a storm shredder.

Mountain Threat

Tropical storms draw their strength from warm ocean water so they don’t do well over land. They do even worse when they encounter mountains. Hispaniola, home to Haiti and the Dominican Republic, is covered with mountains. Pico Duarte in the Dominican Republic reaches more than 10,000 feet into the air, high enough to disrupt the structure of a tropical system.

If the high weakens and the storm moves to the north of Hispaniola, Erika might still be a storm when it gets to the Bahamas.

That patch of ocean is important because it’s warm and there isn’t as much wind shear. Shear can rip a storm apart because winds blow at different directions or speeds at varying altitudes.

Warm Water

The sea-surface temperatures in the southeastern Bahamas are about 84 degrees Fahrenheit (29 Celsius) and even warmer to the north, Jeff Masters, co-founder of Weather Underground, wrote on his blog.

The warm water “would potentially provide plenty of extra fuel for intensification,” he said. Erika could become a hurricane, and on Thursday, the U.S. National Hurricane Center said this is a possibility.

So, say Erika does get to the Bahamas and near Florida’s east coast, what happens next? Just to make things more interesting, there’s a low-pressure system in the southeastern U.S. These systems spin counter-clockwise and could drag Erika north.

“To further complicate matters, steering currents may collapse next week,” allowing Erika to wander offshore for several days, Masters said. 

As of Thursday, Masters gave Erika a 20 percent chance of striking the U.S. as a hurricane, a 30 percent chance that it won’t even get that strong and a 30 percent chance of missing the U.S. entirely.

And he also said there’s a 20 percent chance it may just fall apart.
Here’s hoping.

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