Currently in the Atlantic-Sept. 18, 2022

by Glenn "Hurricane" Schwartz

There have been several concerning developments with Fiona over the weekend:

  1. It's getting bigger (and "wetter").
  2. It's slowing down (as expected)
  3. It's moving toward ultra-warm water
  4. It's tracking a bit farther south, which is bad news for Puerto Rico and possibly Hispaniola
  5. The track farther south keeps it farther away from the strong wind shear (which has kept Fiona from strengthening)
  6. Fiona is getting large enough to help "block out" much of the dry air that surrounds it
Track slightly south + getting larger=bigger flood threat

That satellite loop above not only shows a larger, more intense area of convection, but also those thin clouds on the north and east sides are high clouds representing "outflow". When winds "converge" near the surface and "diverge" at high levels, it's a sign of a structure favorable for intensification. And look at the water it's moving into....

VERY high heat content over Fiona=fuel to strengthen

We don't just look at ocean temperatures to forecast the future of a tropical cyclone. The DEPTH of the warm water is crucial. As a storm moves over an area it "churns up" the ocean, allowing cooler water to come to the surface. It's called UPWELLING. But when the warm water extends far below the surface, the churning just brings up more warm water. That is what the Ocean Heat Content image shows. The Caribbean's red colors represent the warmest waters in the entire Atlantic Basin (the western Caribbean is even more extreme).

So, Fiona tracking SOUTH of Puerto Rico means more trouble: more likely intensification and more hours of torrential rain. Of course, the mountains of Puerto Rico and Hispaniola will work against strengthening.

Still, compare the below model intensity forecasts with what they looked like yesterday:

Model intensity now shows a strengthening hurricane

Instead of practically all models keeping Fiona as a Tropical Storm, they are now all showing intensification to a hurricane, and several show a potential Category 2 or 3 next week.

But here is what it means to the U.S. mainland that the track is going slightly south of where most forecasts had been showing: practically nothing. The computer models and NHC still strongly support Fiona staying away from Florida and the U.S. East Coast. The chance isn't zero-but it's not any higher than it looked yesterday. Only the models that show a very weak Fiona show a chance of a Florida threat next week.

Track likely well east of U.S. coast

So, what we might see next week is an impressive hurricane-but closer to Bermuda than Florida or the U.S. East Coast. And remember, that "Marine Heat Wave" in the North Atlantic may keep Fiona much stronger than in years before the climate warmed the ocean so much.

Glenn "Hurricane" Schwartz