What if 2 storms meet in the Gulf ?
If the two storms headed toward the Gulf of Mexico track closely enough, it could set off a rare moment involving an “intense dance around their common center.”
A National Weather Service post described the phenomenon — known as the Fujiwhara Effect — in those terms after two instances in 2017.
“Their circulations sort of detect each other,” said Lance Wood, a meteorologist with the National Weather Service’s Houston/Galveston office, “and they can start to move around a common point between them.”
Forecasters are keeping an eye on this as Tropical Storm Marco, formerly Tropical Depression 14, and Tropical Storm Laura head toward the Gulf of Mexico. As of Friday, Laura was expected to move toward Florida and the northeastern Gulf, while Marco was headed toward the coast of Texas and/or Louisiana. Both are expected to be in the Gulf of Mexico early next week.
The Fujiwhara Effect is a possibility, Wood said, but it also may not happen. It’s too soon to know.
The phenomenon was named for Sakuhei Fujiwhara, who was director of the Central Meteoro
logical Observatory of Japan and first described the interaction of vortices in water in a 1921 paper. He observed the properties of spinning phenomena such as whirlpools and cyclones and saw when two or more drew close to one another they could affect each others’ the speed, strength and track. The effect can occur when two tropical cyclones get within roughly 900 miles of each other.
It happened twice in 2017, according to the National Weather Service — between hurricanes Hilary and Irwin in the East Pacific and between Typhoon Noru and Tropical Storm Kulap in the West Pacific.
“When two hurricanes spinning in the same direction pass close enough to each other, they begin an intense dance around their common center,” a NWS post from that year said. If one hurricane is stronger, it could absorb the weaker storm. Two storms closer in strength can be drawn toward each other, spinning each other around before shooting off on their own paths or reaching a common point where they merge. Sometimes, the effect is additive when the hurricanes come together and can create one larger storm instead of two smaller ones.
The Fujiwhara Effect was also credited with changing the course of Hurricane Iris in 1995. “The change in heading was probably a consequence of a Fujiwhara
interaction between Iris and Humberto located about 750 (nautical miles) to the east,” a National Hurricane Center post noted.
Wood is not expecting such dramatic results if the two storms interact next week in the Gulf of Mexico. Hypothetically, he described a situation where both storms strengthen to Category 1 hurricanes (meaning their wind speeds are between 74 mph and 95 mph) and were about 900 miles apart. In this scenario, the common point between the two storms would be in the middle of the Gulf of Mexico. This would cause Marco to slow down a little bit. Laura would speed up a little.
This potential change in pace is not expected to make Marco a slow, rainmaking storm like Hurricane Harvey, Wood said.
“It’s probably going to be pretty subtle,” he said.
Wood said the Fujiwhara Effect doesn’t happen very often in tropical cyclones. If it occurs this time, it would be next week, closer to when the storms could make landfall.