In the record-hot Florida fall of 2018, Hurricane Michael was rabid with hidden energy absorbed from a Gulf of Mexico 4 to 6 degrees warmer than normal.
Air molecules heavy with moisture and sizzle, soared on thunderstorm currents into Michael’s eye, releasing latent heat — an invisible smorgasbord of fuel for the burgeoning cyclone.
Twice, the Category 5 hurricane hit warm pools in its trek toward Florida’s Panhandle, downing shots of adrenaline that caused bouts of rapid intensification. One of the surges would keep the storm’s engines revving right into the vulnerable shoreline, defying climatology that says hurricanes weaken as they approach the Gulf Coast.
Michael’s ascent to the top echelon of tropical cyclones was solid physics, but whether the double-barreled rapid intensification events are directly tied to climate change is muddier.
Ingredients of a hurricane
Multiple factors go into creating a potent Cat 5 storm like Michael.
More nuanced, and less understood, environmental machinations are needed for rapid intensification. Playing a role are warmer waters, a moist atmosphere, a defined inner core, light wind shear and a clockwise flow of air in the upper levels of the atmosphere that helps the hurricane breathe.
There are signals, however, that more Cat 4s and 5s with dangerous escalations will increase in a warming climate, a terrifying prospect for forecasters who still grapple with predicting rapid intensification.
“It’s very, very hard to attribute any one event to any kind of external influences,” said Kerry Emanuel, an MIT professor of atmospheric science, about attributing Michael’s intensification to climate change. “Most scientists feel that’s not the way to go. It’s too hard, it’s too dicey. But we can put Michael in the context of climate change and what we are beginning to see.”
Buoys analyzed by Climate Central have shown a 1 to 2 degree increase in the average water temperature in the Gulf of Mexico from August through October in the past 40 years. High temperatures have peaked near 90 degrees, with the average falling closer to 85 degrees.
In October 2018, Florida had just come off back-to-back record-warm months with September’s average temperature reaching 82.3 degrees — 3.2 degrees above normal. August’s temperature was 82.2, which was 2.2 degrees above normal.
That kind of heat, without a fall cool front to knock temperatures down, helped keep the Gulf of Mexico at between 84 and 86 degrees, and set the stage for Hurricane Michael to prosper.
It became the fifth Category 5 hurricane to make landfall in the U.S. since 2016 when it drove into Mexico Beach near noon on Oct. 10.
Michael Mann, a distinguished professor of atmospheric science and director of Pennsylvania State University’s Earth System Science Center, is less hesitant to link climate change to specific storms. He recently co-wrote a column for The Guardian saying that Cat 5 Hurricane Dorian was stronger than it would have been “had we not spent the past 150 years dumping carbon pollution into the atmosphere.”
For every 1 degree Celsius of warming (1.8 Fahrenheit), there is a 7 percent increase in maximum wind speeds and a 23 percent increase in destructive potential, Mann said.
“So it’s fair to say that storms like Dorian have been on average made roughly 25 percent more destructive by human-caused warming of the planet,” Mann said.
NOAA's Geophysical Fluid Dynamics Laboratory recently issued a 20-page synopsis of current research results about global warming and hurricanes.
In summary, it says sea level rise will cause higher coastal inundation levels for tropical cyclones. That means bigger waves and higher storm surge that reaches farther inland.
Hurricane Michael’s surge was estimated between 9 and 14 feet at landfall with the highest inundation happening at Mexico Beach.
The intensity of tropical cyclones likely will increase on average by 1 to 10 percent, with more Category 4 and 5 storms, but the overall number of hurricanes will stay the same or slightly reduce in number.
Also, Emanuel said he expects the odds of hurricanes rapidly intensifying, defined as an increase in wind speeds of 35 mph or more in a 24-hour period, will increase in a warming world. According to one of his studies, a storm that intensifies by 70 mph in the 24 hours before landfall occurred about once per century in the climate of the late 20th Century.
That may occur every five to 10 years by the end of this century if climate change continues without abatement.
“We are confident we will see more rapidly intensifying storms,” Emanuel said.
Hurricane Michael had at least two jolts of rapid intensification, depending on the 24-hour periods examined, said Michael Brennan, senior hurricane specialist for the NHC.
Two are specifically mentioned in the post-mortem analysis of the storm. The first took it from a tropical depression to a tropical storm in just 6 hours and to a hurricane the next day. The second took it from a Category 2 hurricane at 7 a.m. Oct. 9 to a Cat 4 and then a 160-mph Cat 5 at landfall.
Nick Shay, a professor of Ocean Science, and associate dean of research for the University of Miami’s Rosenstiel School of Marine and Atmospheric Science, said the first rapid intensification event happened when the storm ran through a filament of water that had shed off a warm eddy in Gulf of Mexico.
The second warm pool was just off the continental shelf, Shay said.
Both pools were deeply heated, meaning Michael’s churning couldn’t bring up enough cool water to dull the wind speeds. Typically, storms that run over the continental shelf cause an upwelling that works to weaken the storm.
Shay said a warmer world will strengthen some of the factors that lead to rapid intensification, such as warmer water, but that science doesn’t understand yet how all of the processes will work together under climate change.
“Climate change is happening, but how fast and what its relative contributions are during rapid intensity events, I don’t think anyone knows that for sure,” Shay said. “It’s a puzzle. Some pieces fit, some don’t.”
Loss of trees
While there is some debate on the full impact of climate change on the hurricane, what isn't debatable is the destructive mark the storm left on the county's forests and wildlife.
Even a year later, evidence of thousands of bent, snapped and lost trees is plain to see.
“Looking around, it’s a lot,” Julie McConnell, who works for University of Florida Institute of Food and Agricultural Sciences Extension Bay County, said of how many trees were lost. “Even the ones that are standing have sustained some pretty significant damage.”
Fewer trees causes a multitude of effects.
“We’re obviously losing our shade,” McConnell said. “The shade on buildings can help reduce energy costs so that’s going to impact homeowners, building managers as far as different energy costs.”
Erosion issues could also pop up since root systems help hold soil in place.
“One thing we need to be aware of is nature always feels a void,” McConnell said. “We’re seeing a lot of different vegetation pop up. We need to be aware of what’s growing because we do have some plants that can be a problem.”
Invasive species that can be a problem include cogon grass, popcorn trees and the air potato vine. McConnell encouraged people to familiarize themselves with what’s growing and get help from UF/IFAS if they want. UF/IFAS has a Facebook page for more information.
“All of these were in Bay County before the storm,” McConnell said. “This is not something that just came in afterward. Some of the conditions are favorable for them to get out of control.”
The Florida Forest Service has also taken note of how Hurricane Michael affected trees: 72 million tons of forestry trees were left broken, uprooted or blown over and “prime for burning,” according to a talking point sheet. The damaged trees represent “2.5 million log trucks worth of wood across 2.8 million acres spanning 11 counties in the Florida Panhandle,” the FFS sheet stated.
Wildfires have broken out since the storm and continue to be a threat for the foreseeable future.
“The unprecedented volume of damaged trees from Michael resulted in dense pockets of vegetation. There is an average of 58 tons of fuel per acre in the impacted area — 10 times more than before the storm,” the FFS sheet stated. “The exponential increase in fuel loads has created the potential for a significant increase in the number, intensity and danger of wildfires over the next three to 10 years.”
Wildlife and dunes
Hurricane Michael caused landscape level changes in wildlife habitats, though understanding the impacts “may take years,” said Carli Segelson, Florida Fish and Wildlife Conservation Commission public information director for the Division of Habitat and Species Conservation.
“Impacts to individual wildlife species vary, potentially increasing preferred habitats for some species and decreasing the same for others,” Segelson said. “Some species benefit from the creation of new snags, downed woody debris and brush piles. For example, species such as the brown-headed nuthatch, Carolina wren and screech owls may all benefit from new cavities in snags. Downed logs are used as important cover for snakes, shrews, and mice.”
However, species such as red-cockaded woodpeckers, which excavate cavities in living trees, may have a decline in active clusters from the loss of existing cavity trees and scarcity of new trees for cavities.
An article in the FWC Coastal Wildlife Conservation Initiative newsletter gave additional information. As of June, FWC has observed grasses, herbaceous plants, and shrubs slowly recovering on impacted dunes. Because Hurricane Michael occurred late in the marine turtle nesting season, “direct loss of marine turtle nests was limited to the relatively small number of nests still on the beach,” though longer-term storm impacts could affect nesting during the 2019 nesting season.
“The hurricane directly impacted both Choctawhatchee and St. Andrew beach mouse populations,” the article stated. “Approximately two weeks following the storm, biologists were able to access several impacted areas to determine the loss of beach mouse habitat and search for evidence of mice. While impacts to the habitat varied across sites, beach mouse tracks were observed in several places, indicating that some individuals survived the storm.”
Track tubes have been used to detect beach mice in coastal areas, including Rish Park and Tyndall Air Force Base, according to the article. Tyndall was hit hard by the storm.
“During recent live-trapping at Rish Park, biologists captured nine mice in one night. However, similar trapping efforts on Tyndall Air Force Base resulted in much lower capture success, with only four mice captured over a total of four nights,” the article stated. “Although the impacted beach mouse populations will likely continue to grow and expand as the dune habitat recovers, it may take several years and close monitoring to detect any unexpected declines.”