WFLA Exclusive: Study projects alarming increase in major hurricane landfalls

Jeff Berardelli is WFLA’s Chief Meteorologist and Climate Specialist

TAMPA, Fla. (WFLA) — It has been over 100 years since the Tampa Bay Area has seen a direct hit from a major hurricane – Category 3 or higher. But if the models are right, our area may see an astonishing increase in the future.

WFLA partnered with Columbia University to do a study last summer to determine if Tampa Bay’s major hurricane drought has just been a string of good luck— or if the lack of direct hits is just the norm for our area.

Our results showed it’s not luck. Turns out our favorable geography combined with a mild climate like the 20th century meant, statistically speaking, the immediate Tampa Bay Area should only see a major hurricane less than once per century.

While major hurricanes were indeed rare in the cooler climate of the 1900s, what about the warmer climate we are experiencing now— and the even warmer climate we will feel in future decades?

To answer this question the Max Defender 8 Weather Team once again did something unprecedented for a TV station – this time partnering with a division of the Department of Energy.

This summer the team worked to uncover the local details of a cutting-edge climate-hurricane study. The results, discussed below, are so shocking – even to me as a hurricane and climate specialist – I had to check them over for accuracy several times.

Unprecedented Warming :

The global surface temperature has warmed around 2.5 degrees Fahrenheit since pre-industrial times (1850-1900). The reason: overwhelming scientific consensus from copious research shows that humans have inadvertently warmed the climate mainly from the burning of fossil fuels and subsequent release of heat-trapping climate pollution, like carbon dioxide and methane.

It’s not just the atmosphere that has warmed. The Tropical Atlantic Ocean in hurricane season has also warmed around 2.5 degrees Fahrenheit just in the last 30 to 40 years. This provides higher octane fuel for tropical systems once they have formed.

Current Atlantic sea surface temperature anomalies are pictured directly below with reds indicating water temperatures that are above normal.

To date, there have been many studies looking into how a warming climate may impact tropical cyclones in the future. It varies basin by basin, but the general consensus is that the number of storms may actually decrease, while the intensity of storms will likely increase.

The increase in the intensity of storms matters the most because 85% of the damage from tropical cyclones is caused by major hurricanes. A 2020 study found that the trend may already be occurring, finding that the probability of a run-of-the-mill hurricane becoming a major hurricane in the Atlantic Basin is now two times greater than it was four decades ago. Storms that rapidly intensify close to land are also on the increase already.

PNNL/ WFLA Study Details:

Given the extra heat in the climate system, how may the risk for hurricane landfalls – in the Tampa Bay Area and other cities along the Southeast U.S. coast – change in a warmer climate? This was the starting point for our work with the Department of Energy’s Pacific Northwest National Laboratory (PNNL).

Last spring PNNL’s Dr. Karthik Balaguru and co-authors published a study in the journal Science Advances titled, “Increased U.S. coastal hurricane risk under climate change”, finding in the future “enhanced hurricane frequency for the Gulf and lower East Coast regions”.

The research made clear that hurricane risk will likely go up in the future in the Southeast U.S. But we wondered by how much, specifically what areas would see the greatest increase, and what was the cause?

It was those questions that prompted us to reach out to Balaguru and see if we could localize the study, drilling down on the geography and storm numbers. His team was more than willing to help.

To conduct the study Balaguru’s team used nine state-of-the-art global climate models to reconstruct the past climate based on observational data, and also project Earth’s environment in a future warmer climate.

Then using Balaguru’s framework called the “Risk Analysis Framework for Tropical Cyclones” (RAFT) his team used the past and future environments simulated by those climate models to synthesize hundreds of thousands of tropical cyclones in an efficient manner.

In total, the experiment simulated almost a million tropical cyclones – nearly half a million tracks for the historical period (1980-2014) – and nearly half of a million tracks for the future period (2066-2100).

Comparing the computer-generated past tracks, to the computer-generated future tracks, you can get a sense of how landfall patterns change as the climate changes and how much stronger or weaker the systems are.

[One note: you may wonder why computer models were used for a historical period in which records are handy. First, it’s ideal to have an apples-to-apples comparison of the past and future to see how things change. Comparing observations in the past to computer-simulated tracks in the future is not apples to apples.

Also, given the climate of the period 1980-2014, if you somehow could relive that same 35-year climate pattern again and again, the tropical systems produced would never be the same twice due to randomness. Some 35-year periods would produce more storms, some less, some stronger, some weaker and some with more or less landfalls. The point is that a computer model environment allows you to run, and rerun, hurricane track simulations in a climate like that of 1980-2014 thousands of times such that you eventually come up with an average that is representative of that climate. Then, once you do the same for the estimated future climate, you can make an apples-to-apples comparison to assess the changes.]

In this study we examined how the following parameters changed (on a county level) from the historical period to the future period: Tropical storm frequency (sustained winds 39 mph+), hurricane frequency (sustained winds 74 mph +), major hurricanes (sustained winds 130 mph+), maximum wind speed, and maximum rainfall rates.

This data is available on a county-by-county basis along the U.S. Gulf and East Coasts. Although we focused our analysis mainly on the Tampa Bay Area, we will also discuss numbers for Houston, New Orleans, Fort Myers, Miami and Charleston below. The results are listed in the next section.

[It should be noted that Balaguru’s team chose to use a business-as-usual, high-emissions scenario ( SSP5-85 ) for the model’s simulated future climate. This scenario assumes that the nations of the world continue to burn fossil fuels as they are now and do very little to slow heat-trapping emissions down.

While the pledged ambitions of nations are to reduce emissions significantly, it is not entirely clear how much or how fast that will occur. That is one of the inherent uncertainties of modeling the future. So I asked Balaguru why they chose a high emissions scenario as opposed to an intermediate one.

Balaguru said that using a high emissions scenario allows policymakers and planners to assess a worst-case scenario. He also explained, “There is research to show that this [high-end] forcing is plausible and there is a realistic chance that this could happen.” With that said, Balaguru is planning to do another study soon using an intermediate scenario.]

Study Results:

For all the areas examined a robust increase in landfalling tropical cyclones from the historical period (1980-2014) to the future period (2066-2100) was observed. The largest increases were across the state of Florida, with big increases also in the central and western Gulf, and slightly less significant increases along the Southeast Coast. In addition, there were significant increases in maximum rainfall rates and maximum wind speeds.

Tampa Bay Area Results:

The most shocking result from the experiment is the projected increase in major hurricane winds in the later part of this century. The study found the incidence of major hurricanes in the Tampa Bay Area counties may more than triple!

For instance, the study found that historically the Tampa Bay Area should only experience major hurricanes (winds 130mph+) approximately once every 85 years. But in the future, the incidence of major hurricane winds happen once every 27 years – a 215% increase.

To put it another way, in the historical climate a person living in the area should only have expected to experience a direct hit from a major hurricane once in their lifetime. But starting later this century it may very well be an average of three times a lifetime – or once per 30-year mortgage cycle.

The experiment also showed, for the period 2066-2100, a 75% increase in events with hurricane-force winds and a 39% increase in events with tropical storm-force winds. Maximum wind speeds increase by 15% to 20% and maximum rainfall rates increase by a staggering 50%.

To put these numbers into perspective, a 20% increase in maximum winds would mean a hurricane with winds of 150 mph in the 20th century could have winds of 180 mph later this century. The increase in winds means the damage potential could increase by about four times .

Increased rainfall rates from climate change can also have a huge impact. Dr. Michael Wehner, who was also coincidentally a co-author of Balaguru’s 2023 study, found that climate change likely caused Houston’s Hurricane Harvey to ring out roughly 20% more rainfall than it otherwise would have in a cooler climate. As a result, 30% more homes likely flooded leading to around $50 billion of extra damage.

Now before we discuss the results for the other cities examined (we will do that at the bottom of this article) let’s discuss why the global climate models project an increase in landfalls in the Southeast U.S.

Reason for more landfalling hurricanes:

While it is easy to assume the greater number of hurricane events on the Southeast U.S. Coast is directly due to hotter water, it turns out, that is not the main reason. Sure, the hotter water can explain much of the reason for the stronger winds and the heavier rainfall rates, but it turns out the bigger influence on more landfalling hurricanes is a change in circulation patterns.

The climate models Balaguru used for this experiment project robust warming in the Eastern Tropical Pacific in the coming decades and that causes a change in Western Atlantic steering patterns.

The mechanism works this way: Warmer Pacific waters invigorate waves of atmospheric energy, called Rossby waves, to move from the Tropical Pacific into the Tropical Atlantic. Those waves of energy cause an upper-level cyclonic circulation and low pressure (as seen in the blue shading in the below image from Balaguru’s study) to form over the Western Atlantic, Caribbean, and Central America. That change in steering directs storms north and northwestward towards the U.S. Southeast and Gulf coasts.

In addition to more cyclones being steered toward the U.S., the models project decreasing wind shear close to the U.S. Coast. That lower wind shear means storms would face a less hostile environment and that would likely lead to stronger landfalling hurricanes.

It should be mentioned that although the consensus of the nine climate models used by Balaguru projects significant warming in the Eastern Tropical Pacific in the coming decades, this is a heavily debated area of uncertainty among scientists . The community is simply not sure if this warming will indeed pan out. If the Eastern Pacific does not warm the way models expect, that would significantly alter the outcome of Balaguru’s study.

Results for other U.S. Cities:

The following is a list of expected changes in hurricane parameters from the model output of the historical period (1980-2014) compared to the future period (2066-2100) in selected cities along the U.S. Gulf and Southeast coasts.

In the Miami area, historically major hurricanes (Cat. 3 +) make a direct hit around once every 80 years, but in the future the study projects that the reoccurrence increases to once per 22 years – a 260% increase. The study also projects a 110% increase in hurricane events, a 50% increase in tropical storms, a 15% to 20% increase in maximum winds, and a 50% increase in maximum rainfall rates.

In the Fort Myers area, historically major hurricanes (Cat. 3 +) make a direct hit around once every 80 years, but in the future the study projects that the reoccurrence increases to once per 22 years – a 260% increase. The study also projects an 85% increase in hurricane events, a 45% increase in tropical storms, a 15% to 20% increase in maximum winds, and a 50% increase in maximum rainfall rates.

In the New Orleans area, historically major hurricanes (Cat. 3 +) would make a direct hit around once every 70 years, but in the future the study projects that the reoccurrence increases to once per 29 years – a 135% increase. The study also projects a 60% increase in hurricane events, a 42% increase in tropical storms, a 15% to 20% increase in maximum winds, and a 45% increase in maximum rainfall rates.

In the Houston area, historically major hurricanes (Cat. 3 +) make a direct hit around once every 180 years, but in the future the study projects that the reoccurrence increases to once per 80 years – a 135% increase. The study also projects a 64% increase in hurricane events, a 42% increase in tropical storms, a 10% increase in maximum winds, and a 40% to 50% increase in maximum rainfall rates.

In the Charleston, South Carolina area, historically major hurricanes (Cat. 3 +) make a direct hit around once every 300 years, but in the future the study projects that the reoccurrence increases to around once per 200 years – a 60% increase. The study also projects a 30% increase in hurricane events, a 22% increase in tropical storms, a 5% increase in maximum winds, and a 30% to 40% increase in maximum rainfall rates.

Conclusion:

The numbers above are clearly stunning and we hope to avoid a future like this.

Given the uncertainties which exist, whether it be the accuracy of the computer models response to greenhouse gas forcing or the nation’s future efforts – or lack thereof – to reel in greenhouse gases, it is worth mentioning that these results should be contemplated with a healthy degree of skeptism.

Computer models are very useful in projecting general trends but often less accurate in determining details. So will Tampa really see a 3X spike in landfalling major hurricanes later this century? Who knows. But I do think it’s important to take seriously the trends that the models suggest.

We know hurricanes of the future will dump significantly more rain. It is very likely that hurricanes of the future will be able to achieve significantly stronger winds. This study shows both of these clear signals which climate scientists generally agree on. So that’s a sign the models are on to something.

The bottom line is: the threat for more landfalling, stronger, more-impactful hurricanes seems like a straight forward conclusion as the planet continues to warm, as seas continue to rise, and people continue to build in harm’s way. We must as a society prepare for a more extreme future.

It’s also important to mention that the future is not written yet and humanity is still in the drivers seat. It won’t be easy, but if nation’s start taking the threat of climate change seriously and reel in our carbon emissions, then it is very likely we can curb some of these impacts. The ball is in our court.

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