Bryan Norcross tackles more hurricane season questions with expert insight

As the calendar nears ready to flip to August and marches closer to the more active periods of hurricane season, FOX Weather held a live Q&A session with Hurricane Specialist Bryan Norcross, who answered a range of questions. 

Why do some hurricanes have larger eyes than others?

Norcross says hurricanes come in every variety -- some have giant eyes; others quite small.  Hurricane Wilma in 2005 managed to do both. When the storm was in the Caribbean, it had a small eye just 2 miles across.

"It was this super pinhole eye that none of us had ever seen before," Norcross said. "And when you get the super pinhole eye, the idea of the figure skater spinning and bringing in the arms and spinning faster and faster when the arms are really the maximum speed. So that's when you get the lowest (atmospheric) pressure. That's when we got the 882 millibars with Wilma."

But Wilma's eye grew as the storm interacted with nearby land masses and later reformed, and was much larger by the time it circled back and reached Florida. 

"Very often, what happens is the eye gets bigger as it reforms, and sometimes it gets bigger into a state that gets kind of stable," Norcross said. "We saw this with Hurricane Frances in 2004 as well. Came in with this kind of giant eye. It was kind of in a stable configuration, a gyre-type configuration... So storms that last a while, their eyes grow and shrink and grow and shrink.   So storms just come in all these varieties and the eyes get bigger through internal processes and sometimes because they get disrupted and that's how they reform."

Are forecasters going to start using AI?

Norcross says the process has already begun.

"We actually have used a little bit of it on FOX Weather now and then," he said. "But yes, we're watching especially closely the European Center AI model called the AIFS and the Google Experimental AI model... we'll call it Google AI."

Norcross says we'll include those new models with the typical models, the European and the GFS model.

"The testing that's been done on those AI models is shown to be quite reliable and worth considering when we consider these sorts of forecasts, especially long-range," he said.

How significantly has forecasting improved over the past 10-15 years and why?

Norcross says more powerful computers are credited with increasing forecast accuracy over the past decade or so.

"That means that we can process more data," he said.

"The data that gets processed is put on a grid... and the calculations are made all the way around the Earth. So, the more grid points you have, the better you understand the weather, because there are small features in the weather and there are big features in the weather. We normally forecast the big features pretty well, but now we're getting to forecast the smaller features."

And part of that equation is indeed the advancements made in AI, especially for hurricane forecasts.

"All of this is very, very new, obviously. And so there's a lot of learning going on, but the initial impression of the AI forecast is very good," he said.  "There's some indication that as we get higher resolution data into the AI models that maybe they can understand intensity better and figure that out.  This is the first year that we're really getting a look at this in real time with real hurricanes.... Now, will the forecast continue to get better in the future? That's a great question. The answer is probably yes, but not at the same rate. The rate of improvement, it's kind of flattening out, but it's continuing to go down in terms of the average errors a little bit at a time."

Where does naming an invest come from? What does that number mean?

Invests come from an internal system at the National Hurricane Center, Norcross says.

WHAT IS AN INVEST?

"It was never really intended for public use, but here we are in the modern world, so now it's a public thing. And they just have this convention that they start numbering at 90, and they go to 99, they go back to 90," he said. "So every time they want to investigate something, but it's not organized enough to get a name or to be a tropical depression. Then it just gets the next number in the 90s. And yes, it's arcane and weird, and hopefully someday they'll do something that's not quite so internal, but that's what we have right now."

How does the Madden-Julian Oscillation affect the Main Development Region?

Norcross says the Madden-Julian Oscillation (MJO) is a broad-based pulse that revolves around the world.

"And as it comes by, it enhances storm development, and as it goes past, then it suppresses storm development," Norcross said. "We've been in generally a suppressive phase this hurricane season over the Atlantic."

WHAT IS THE MADDDEN-JULIAN OSCILLATION?

The MJO pulses originate over Southeast Asia -- essentially, Indonesia -- and they slowly move across the Pacific. Norcross says it normally takes 40 days to go around the globe, but sometimes they just fizzle out, or we can't detect them.

One recent example was an MJO pulse that energized the eastern Pacific tropics, where the basin set records for some of the earliest named storms and is already past the 'F'-named storm.

"We thought it might get to the Atlantic and enhance activity in the Atlantic, but it just kind of died out," he said. "...But we watch it especially as we get here toward the heart of the hurricane season. Really, once the ocean water is plenty warm, they really can trigger more thunderstorm development, and that energy is what triggers the development of tropical storms and hurricanes."