Will we see a Fujiwhara effect between Philippe and Rina?

Will We See Fujiwhara Effect? Twin Spin in Atlantic

Weather buffs could soon be treated to a rare event: the Fujiwhara Effect. That’s when one tropical storm collides with another. Topical Storm Philippe is being overtaken by the newly formed Tropical Storm Rina. See the satellite image below taken around 12:30 PM CDT.

12:20 pm Houston time
Two hours and forty minutes later.

Will They Merge?

I asked Harris County Meteorologist Jeff Lindner what happens in such a case. His response:

“Generally speaking the weaker system will rotate around the stronger system. This is known as the Fujiwhara Effect.”

Harris County Meteorologist Jeff Lindner

Wikipedia offers a great description of this rare event and some of the parameters necessary for it to occur.

“The effect occurs,” says Wikipedia, when two nearby cyclonic vortices move around each other and close the distance between the circulations of their corresponding low-pressure areas. The effect is named after Sakuhei Fujiwhara, the Japanese meteorologist who initially described the effect. Binary interaction of smaller circulations can cause the development of a larger cyclone, or cause two cyclones to merge into one. … Tropical cyclones typically interact within 870 mi. of each other.”

These storms are already within that radius. At this hour (3:30 PM CDT on 9/28/23), the centers of Philippe and Rina are 631 miles apart, but their outer bands are already interacting as you can see in the photos above. And the effect will likely become stronger.

Philippe (left) is moving at 2 mph and Rina at 10 mph. So they will come even closer.

Cones of Uncertainty

The two maps below show projected tracks for the next few days. But remember, the center of the storm has an equal chance of passing through any point within the cone of uncertainty.

Here’s the cone for Philippe.

Here’s the cone for Rina.

Pick a spot on the grid and compare the projected locations over time.

Wikipedia says, “Rotation rates accelerate when tropical cyclones close within 400 mi of each other. Systems typically merge when they are within 190 mi of one another.”

So we have at least a few days to watch these two and a developing Fujiwhara effect if any.

At an 8 mph closing rate, two storms 631 miles apart would take about 2.5 days to get within 190 miles of each other.

How to See if They Merge

Mergers are fairly rare, according to Wikipedia. But these two could tango. So watch to see if they merge over the next few days. Exact predictions are difficult, because of the uncertainty associated with storm tracks.

However, you can check their progress and proximity visually by looking at the satellite images on NOAA’s National Hurricane Center website. Select from several different options within the “Atlantic-Wide View”: Geo-Color, Visible, Short Wave IR, Infrared, and Water Vapor.

Regardless of what happens, NOAA does not predict that these storms will come anywhere close to Texas. So sleep easy.

Posted by Bob Rehak on 9/28/23

2221 Days since Hurricane Harvey