Weather Explainers

Twin Lows Do a Fujiwhara Dance Off East Coast, Resembling a Face in Satellite Imagery

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Twin low-pressure systems danced around one another off the Carolina coast Tuesday in a process called the Fujiwhara effect.

The dance, more typically seen with hurricanes and other tropical low-pressure systems, occurs when two weather systems get a little too close to one another.

Two lows swirl around each other on the GOES-East satellite on Tuesday, Feb. 5, 2019. The pink colors show where there are high cloud tops during the day, and the white clouds are shallow.
(GOES-East, RAMMB/Colorado State University)

These lows developed just off the coast of North Carolina on Monday as a picturesque but weak singular low-pressure system with a clear cold front to the east extending to near Bermuda.

A second low-pressure system developed along the weakening frontal boundary, which then got pulled north and west by the initial low-pressure system.

By midday Tuesday, the weaker low had migrated counterclockwise and to the left of the initial low-pressure area, resembling a pair of eyes.

The larger circulation of the primary low still allowed shallow clouds to percolate around both low-pressure systems, giving the appearance of a face, including a mouth and even a chin.

Satellite imagery from the afternoon of Tuesday, Feb. 5, 2019, showing two swirly low-pressure systems and a wide circulation of clouds around the two twins, making up the rest of an apparent face.
(GOES-East, RAMMB/Colorado State University)

The Fujiwhara effect can have two endings: one where the stronger low-pressure system absorbs the weaker system, and the other where the low-pressure systems eventually move away from one another.

In this case, because the two lows were very weak, the systems eventually went their separate ways out into the open Atlantic.

The Fujiwhara effect, named for Dr. Sakuhei Fujiwhara, the meteorologist who first described the phenomenon in 1921, is the rotation of two weather systems around each other in close distance.

As mentioned before, this symbiotic rotation is often seen in tropical cyclones around the world, especially in the busiest world basins, like the Western and Eastern Pacific.

The most recent example close to North America occurred last August near the western coast of Mexico. Hurricane John absorbed weaker Tropical Storm Ileana as both storms paralleled the Mexican coast.

In the tropics, the Fujiwhara effect occurs most notably in the Western Pacific about one to two times per year. Globally, it occurs less than a dozen times each year.