What happens when two tropical storms approach each other? WAVE 3 meteorologist Tawana Andrew tells us about the Fujiwara effect. The transcript below was lightly edited for clarity .
Bill Burton: It's time for us to take a look at the Science Behind the Forecast, as I am joined by WAVE 3 meteorologist Tawana Andrew. Good morning, Tawana.
Tawana Andrew: Good morning. Today, we're talking about weather history happening in real time.
BB: Yeah, we're talking about something in real time, exactly as you said it. We're talking about the Fujiwara effect, and that's important because of the rain we're getting now, we're seeing it now, aren't we?
TA: Yes we are. We're watching what's left of hurricane Helene, basically fading off the map, but interacting with another low [system] in a very special way. So, the Fujiwara effect is named after a Japanese meteorologist who wrote about it all the way back in 1921. And of course, the National Weather Service has a very straightforward definition of it.
BB: Of course.
TA: It defines the Fujiwara effect as a binary interaction where tropical cyclones within a certain distance of each other will begin to rotate around a common midpoint.
BB: Sure, perfectly clear.
TA: So in English, that's when two tropical cyclones get less than 870 miles away from each other, they can start to interact and even rotate around one another. This can also happen with a typical mid latitude cyclone. So those lows that we typically see moving through the U.S. with cold fronts and warm fronts and such that can also happen with them, but that will happen when they get within 1200 miles of each other.
This is very interesting, because with a tropical cyclone — with hurricanes — if the storms are about the same size, then they'll start to rotate counterclockwise (because we're in the northern hemisphere) around a spot in between the two storms. So these storms will literally start to dance around each other.
If one storm is stronger than the other, then the smaller one and the weaker one will eventually orbit it and then crash into the larger storm while being absorbed... But if they're in similar sizes and similar strengths, what will happen is that one is more likely to move towards the other before they reach a common point. They will merge, or they can start to spin around each other and basically shoot off into different directions, kind of like when we played with tops back in the day.
BB: That's exactly what it's like.
TA: So you're seeing that, but in the atmosphere and in rare circumstances, hurricanes can actually combine into one larger storm, so like a Hollywood movie, but in reality.
BB: Coming soon to a theater near you!
TA: Hopefully, scientifically accurate.
It's not entirely uncommon for two tropical cyclones to interact with each other, because it has been documented on a number of occasions. Back in 1995, hurricane Iris was weakened after an interaction with Humberto, but later got stronger. And then that same hurricane, Iris, went back and absorbed another tropical storm named Karen.
So this is the something we see [but] doesn't happen often. It's just rare to see the Fujiwara effect happening with the remnant of a tropical system and a mid latitude cyclone. So if your weather nerd friends are very excited right now and they're watching a lot of satellite imagery, this is why.
