Why "It Hasn't Happened in 100 Years" Doesn't Mean It Won't Happen: The Case of Milton and Tampa Bay

As Hurricane Milton is forecasted to potentially hit Tampa Bay, I'm reminded of the many times friends in Tampa Bay would comfort themselves with a common belief:

“It’s been 100 years since Tampa had a direct hit, so we probably won’t get one now.”

This logic sounds reassuring, but it’s based on a misunderstanding of how probability works.

The fact that Tampa Bay hasn’t had a direct hit in over a century doesn’t mean it’s safe or that it won’t happen soon. In fact, this reasoning can actually make us underprepared for an event that could have devastating consequences.

Let’s explore why.

The Misleading Comfort of Long Periods Without an Event

When people say, “It hasn’t happened in 100 years,” they often assume that the long stretch of time without a hurricane means they’re in the clear. This mindset reflects a belief that the past protects us from the future: since a hurricane hasn’t hit for a century, people believe the chances of it happening now must be lower.

But that’s not how probability works.

In probability theory, each year’s likelihood of a hurricane hitting Tampa Bay remains the same, regardless of how long it’s been since the last one. If we assume a 1% chance of a direct hit every year, that 1% chance applies this year, next year, and every year moving forward, no matter how long it’s been since the last hurricane. In other words, the past doesn’t change the future risk.

This belief that "we’re safe because it hasn’t happened in a while" is a cognitive bias known as recency bias, where people tend to overemphasize recent history and assume that future outcomes will follow the same trend. The long stretch of time without a hurricane gives a false sense of security, making people believe that Tampa Bay is somehow "protected" from another direct hit.

The Reality of Long-Term Averages

The idea that a hurricane is expected to hit Tampa Bay "once every 100 years" is based on a long-term average, but that average can be misleading in real life. Here’s why:

1. Hurricanes Don’t Follow a Schedule: The fact that Tampa Bay hasn’t had a direct hit in over a century doesn’t mean hurricanes are spaced out evenly every 100 years. It’s possible to go 150 or 200 years without a hurricane and then get two within a few decades. The "100-year" figure is just a statistical average over a very long period.

2. Probabilities Are Consistent Over Time: Each year, the chance of a hurricane hitting remains about 1%, regardless of how many years have passed without one. So, whether it’s been 5 years or 100 years, that 1% chance is the same. Just because Tampa Bay has avoided a direct hit for over 100 years doesn’t mean it won’t happen tomorrow.

3. The Law of Averages Is Not Predictive: While long-term averages suggest that Tampa Bay could experience a direct hit once every 100 years, this isn’t predictive of when the next hurricane will occur. It’s not as if hurricanes are "scheduled" to happen at fixed intervals. Instead, the 1% chance per year simply means that over a long period of time, Tampa Bay will, on average, get one hurricane every century.

The Danger of Underestimating Risk

The real danger in thinking that "it hasn’t happened, so it won’t happen" is that it leads to complacency. This false sense of security can result in communities under-preparing for a potential disaster. In reality, long periods without a hurricane can sometimes lead people to believe that they are less vulnerable, when in fact the risk remains constant year after year.

For example, after a century of no direct hits, Tampa Bay residents may not have invested in hurricane-proof infrastructure, made adequate evacuation plans, or stocked up on emergency supplies. Yet the very nature of a low-probability, high-impact event like a hurricane means that it’s essential to be prepared, even if it hasn’t happened in recent memory.

The Role of Changing Environmental Factors

It’s also important to recognize that while the basic probability of a hurricane hitting Tampa Bay might remain steady over time, environmental factors can shift these probabilities. For instance:

The Climate Does Change Over Time: As the climate warms, scientists are predicting that hurricanes may become more frequent and more intense. This means that the historical 1% annual probability might no longer hold true. In fact, some models suggest that certain areas, including parts of Florida, could see an increased likelihood of hurricanes over the coming decades.
Changing Weather Patterns: Natural climate patterns, like El Niño or La Niña, can affect the likelihood of hurricanes in any given year. Some years might be more favorable for hurricanes, while others see a lull in activity. This introduces variability that can further complicate long-term averages.

A Better Approach: Managing Risk, Not Just Probabilities

Given all this, how should residents of Tampa Bay—or any area prone to natural disasters—approach the risk of hurricanes?

Understand the True Nature of Probability: Just because Tampa Bay hasn’t had a direct hit in over 100 years doesn’t mean it’s less likely to happen now. Each year carries its own independent risk. Prepare accordingly.
Plan for the Impact, Not the Probability: Even if the chance of a hurricane is 1% each year, the impact of that event can be catastrophic. It’s essential to focus not just on the probability but on the potential consequences. Proper infrastructure, emergency planning, and early warning systems are critical.
Don’t Rely on the Past: It’s tempting to look at the past and assume the future will be the same. But nature doesn’t follow past patterns, and the environment is changing. Just because something hasn’t happened in a long time doesn’t mean it won’t happen tomorrow. In fact, the longer we go without a hurricane, the closer we are to experiencing one again, in the sense that averages play out over long periods.

Conclusion: Don’t Let 100 Years of Calm Fool You

As Hurricane Milton approaches Tampa Bay, it’s crucial to break free from the false belief that long stretches without an event mean safety. While it’s comforting to think that the past protects us, probability tells a different story. Each year carries its own risk, and the fact that Tampa Bay hasn’t had a direct hit in over a century doesn’t mean one isn’t coming.

I always replied with an explanation focused on thinking in terms of managing real-world risk. Just as probability is often misunderstood, it's also misused for real-world decisions. If you've gone many years without a hurricane, the math doesn’t say you’re due, but it might make sense to act as if the risk is growing, given your local conditions.

Think of it as a hedge.

The key is to focus on preparation and resilience, not on whether history suggests you're safe. In the end, probabilities are about managing risk, not about making predictions based on the past.

Are you prepared for the unexpected? At Shell Capital Management, we help you manage uncertainty and make better financial decisions—just as you’d prepare for a hurricane, you should prepare for market volatility and other unpredictable events.

Learn more: When Probability Conflicts with Robust Risk Management