Before Michael became a named storm, it started as any other potential hurricane does, as a tropical wave – a cluster of thunderstorms with no defined center of circulation. Within a week it turned into what would become the most destructive storm to hit the Florida Panhandle in recorded history, and one of the worst overall in U.S. history.
As the storm moved across the Gulf of Mexico early last week, it fed off the fuel of very warm waters and very little wind shear. It gained strength and within a few days became Tropical Storm Michael on the morning of October 8, just two days before landfall, quickly becoming a hurricane later that day.
Also, satellite imagery revealed hot towers – tall, powerful thunderstorms – around the eye wall. First discovered in satellite and radar images by NASA scientist Dr. Joanne Simpson in the 1950s, hot towers have been known to add lots of energy to hurricanes.
According to a NASA press release in 2004: “When these tall clouds, called “hot towers,” are present, they double the chance that a hurricane will gather strength within hours…Warm air rises, and these towers are called “hot” because they rise very high due to a large amount of heat, called latent heat. Water vapor releases this latent heat as it condenses into liquid.”
Forecasters at the National Hurricane Center could tell that the Michael would get stronger and warned of it potentially reaching at least Category 3 status. What forecasters failed to diagnose were Michael’s quick explosions of power, a process called rapid intensification that occurs when hurricane winds climb 35 mph in 24 hours. Michael underwent three of these, very fast, between Monday morning and landfall Wednesday afternoon. It wound up at the top of the Cat 4 range with 155 mph sustained winds at landfall.
“That’s one of our biggest forecast challenges and we’re pretty up front that rapid strengthening is not something the models do really well,” Mike Brennan, chief of the hurricane specialists unit at the National Hurricane Center in Miami told the Miami Herald.
The National Oceanic and Atmospheric Administration (NOAA) launched a 10-year project to improve intensity forecast after the brutal 2005 hurricane season spawned Katrina and Wilma. The project was extended, given the poor results: out of 39 instances of rapid intensification during the 2017 season, forecasters got six correct.
Part of that research opened up debate over where to focus attention and limited resources: on the ocean or the atmosphere? Increasingly, and with Michael as the latest example, the answer is ocean.
It’s not unusual for hurricanes to make direct hits or nearly direct hits on Florida in October. Ten of the 36 major hurricanes to hit the state since 1851 have occurred in October. In the Gulf it’s still summer despite what the calendar says. Gulf waters remain warm, and this year temperatures were 3.5°-5.5° Fahrenheit above normal which some people blame on climate change.
Since the 1950s, the Gulf has in fact only warmed by about one degree Celsius (2.8° Fahrenheit), which doesn’t seem like a lot. However, Ben Kirtman, an atmospheric scientist at Rosenstiel and a lead author on the United Nations’ International Panel on Climate Change 2014 assessment, says this can trigger exponential changes.
“When we have one degree of warming we have much bigger increases in evaporation in the atmosphere and we know water evaporation is fuel for the storm,” says Kirtman. “There’s a lot of potential other factors, but that’s the simplest one.”
Kirtman says it’s impossible to blame a single storm like Michael on climate change, but he believes the earth’s system is being primed for more frequent intense storms.
“We have a warmer ocean, a warmer atmosphere and all those things come together to increase the probability of a storm like Michael happening,” he adds. “That’s our scientific understanding. We don’t have much more depth than that.”
Meteorologists are also studying how temperatures might change along a hurricane’s path, how deep they go, and what role the Gulf’s Loop Current plays. The Loop Current is responsible for sustaining very high heat content in the water.
Hurricane Michael made landfall just two days after the United Nations released a major report on climate change, concluding that potentially irreversible and major consequences, including extreme weather events, will grow far worse much earlier than previously thought.
However, at least one study on trends in rapidly intensifying storms did not find statistically significant trends taking place in the western Atlantic (including the Gulf of Mexico), where Hurricane Michael gained strength.