Tropical Storm Philippe forecast to strengthen – could come uncomfortably close to the islands

Tropical Storm Philippe is the apparent winner of the two-storm dance-off that’s been playing out in the Atlantic just east of the Caribbean. In an unusual but not unheard of move, Tropical Storm Rina butted into Philippe’s oceanic space on Thursday at more-or-less equal intensity to a weakening Philippe.

When two storms come close to each other, especially if they are similar in size and strength, the circulations interact in a way that causes the systems to rotate around a nominal central point in a counterclockwise direction. It’s called the Fujiwara effect or a binary interaction.

This merry-go-round of storms rarely has a fairytale ending, however. Quite often, one storm ends up dominating the other. In this case, upper-level winds were stronger over Rina, ripping the storm apart. As a result, Tropical Storm Rina appears destined to limp off stage right into the central Atlantic and die.

Philippe, on the other hand, has been just outside the band of storm-killing upper winds as it drifts south in its roll in the Fujiwara twist.

The strong consensus is that Philippe will move north of the islands and strengthen into a hurricane well away from land. What’s less certain is what’s going to happen in the short term.

The National Hurricane Center forecast calls for Philippe to drift around the Atlantic waters just northeast of the Caribbean islands over the weekend, then begin strengthening and pulling away to the north late tomorrow into Monday. If Philippe stays weaker longer, however, it could take longer to turn north.

Most computer forecasts show Philippe making its north turn comfortably to the east of the islands, but not all. There is still a possibility of a weak to moderate tropical storm affecting the northeastern Caribbean, perhaps as far west as the Virgin Islands. That appears to be the less likely scenario. Still, the odds are sufficiently high that everybody in Puerto Rico and the surrounding islands needs to stay informed until it’s clear that Philippe has made its turn north.

The system will be moving slowly, so it’s not going to pounce. We should know by Monday if the coast is clear or not.

Otherwise, there is nothing obvious on the horizon, and the upper-air pattern across the tropics is turning more hostile to development. But the waters are still spectacularly warm, so if a system found a hospitable patch of atmosphere, it would have extra energy to work with. So we watch.