Philippe to become Category 1 hurricane; Rina to dissipate early next week

FORT LAUDERDALE, Fla. — Neighboring Tropical Storm Rina and Tropical Storm Philippe are continuing to interact this weekend, with Philippe expected to become a Category 1 hurricane and steer a weakening Rina to the northwest.

The phenomenon of two tropical systems interacting is not a common one in the Atlantic.

Tropical Storm Rina was several hundred miles to Tropical Storm Philippe’s east-northeast, and the “more pronounced binary interaction” with Rina had moved Philippe slightly farther to the south than forecasters expected, the National Hurricane Center said early Saturday.

The National Oceanic and Atmospheric Administration says the Fujiwhara Effect is a binary interaction where two tropical cyclones within 345 miles to about 860 miles of each other start to spin around a common point.

The bigger of the two sometimes absorbs the smaller storm, or the smaller storm “will satellite around” the bigger, Craig Setzer, a hurricane preparedness specialist, said.

The National Hurricane Center describes the Fujiwhara Effect as “an intense dance around their common center.” The smaller storm, after orbiting the bigger, can “eventually come crashing into its vortex” and be absorbed.

“Two storms closer in strength can gravitate towards each other until they reach a common point and merge, or merely spin each other around for a while before shooting off on their own paths,” the National Hurricane Center says. Rarely, it can create one larger storm rather than two smaller ones.

Philippe is expected to continue strengthening in the next few days and reach Category 1 strength by Tuesday while Rina will gradually weekend this weekend and dissipate by early next week.

No coastal watches or warnings have been issued for either storm as they spin in the open Atlantic Ocean far from land, but swells from Philippe will affect parts of the northern Leeward Islands, the U.S Virgin Islands and Puerto Rico through the early parts of next week and could cause dangerous rip currents and surf, according to the NHC.

Rina was located about 810 miles east-northeast of the northern Leeward Islands in the far eastern Caribbean, moving northwest at 14 mph, as of 5 p.m. Saturday. Its maximum sustained winds were 45 mph, slightly weaker from 50 mph earlier in the day. Rina’s tropical-storm-force winds extended out to 80 miles.

Rina is expected to continue moving northwest through Sunday along the northern edge of Philippe, then turn north on Monday and dissipate early next week, the latest forecast said. Strong wind shear will remain until it dissipates.

The NHC forecast has Rina’s wind speeds dropping to 40 mph, just over the minimum 39 mph wind speeds to be classified a tropical storm, by Sunday morning and losing its tropical-storm status by Sunday evening.

As of 5 p.m. Saturday, Philippe was located about 455 miles east-southeast of the northern Leeward Islands, moving southwest at 5 mph. Its maximum sustained winds slightly increased to 50 mph from 45 mph Friday. Tropical-storm-force winds extended out to 150 miles.

Philippe will move more quickly to the west-northwest and northwest into Monday, then turn north Tuesday, the latest advisory said. The storm will only moderately strengthen in the next day or so while it battles with wind shear, though forecasters expect more strengthening after that over the warm waters of the Atlantic.

“In the near term, the models suggest Philippe will not move very much and could drift erratically through early Sunday while Tropical Storm Rina passes to its north,” forecasters said late Saturday afternoon.

The forecast for Philippe’s maximum wind speeds had increased by late Saturday afternoon to 90 mph by Wednesday, which is Category 1 strength.

Setzer said the type of interference between Rina and Philippe is more commonly seen in the Pacific rather than the Atlantic.

“The Atlantic, despite the fact that we do get hurricanes in it, is really not a real favorable hurricane environment,” he said. “Conditions have to be just right to get hurricanes in the Atlantic. … So because we have fewer of these hurricanes in general in the Atlantic, we just don’t see this type of interaction as much.”

And when two storms do interact, it doesn’t necessarily mean it combines into one storm that’s twice as large, Setzer said. He described it as each storm existing “in almost like a cocoon in a way.” Storms create their own wind shear on their periphery that can weaken other storms.

“So that out process on the outside of the storm creates wind shear, so when you have two storms that try to merge, especially if they are the same size, they kind of disrupt each other’s whole circulation, and that’s why it’s hard to have two storms just congeal into one bigger storm,” he said. “They just don’t do that. They tend to disrupt each other.”

“It’s possible a bigger storm can absorb a smaller storm and to an extent use moisture inside that storm and grow from it, but … the storm that survives isn’t necessarily going to be twice as big,” Setzer said.

Typically when two storms do end up orbiting each other in a Fujiwhara Effect, Setzer said, they’re usually “fairly healthy and fairly mature,” unlike Philippe and Rina.

So far this season in the Atlantic, there have been 16 named storms, six of which were hurricanes. Of those, three were major hurricanes, meaning Category 3 or above.

Those were Hurricane Lee, a rare Category 5; Hurricane Franklin, a Category 4; and Hurricane Idalia, which made landfall on Florida’s Big Bend region at Category 3 strength on Aug. 30.

The next named storm will be Sean.

Hurricane season officially runs through Nov. 30.