Investing in catastrophe bonds means you are betting against damage stemming from a natural disaster, and many times that’s tied to hurricane risk. Each year, the Atlantic hurricane season poses new threats and begs the question: how bad will it be? That answer comes from climatologists running sophisticated prediction models to determine the number and severity of storms that can be expected.
As a cat bond investor, it’s important to understand how these models work and the factors that influence them so you can make more informed decisions. Here we breakdown how climatologists determine what kind of hurricane season is around the corner.
It Starts with the Ocean
To better understand hurricane predictions models, it’s important to take a step back to understand how hurricanes work. Hurricanes start as a string of rain showers or thunderstorms, but gain strength when they collide with an area of low pressure and warm ocean water. The low air pressure draws the hot, humid air upward into a spiral shape, and as it rises and cools, it condenses into clouds and storms - all while more warm air is sucked in, intensifying the spiral.
In simple terms, hurricanes are heat engines, and pull energy away from warm ocean water. It’s because of this that the first indicator climatologists look at is the sea surface temperature (SST). Climatologists focus their search along the Atlantic’s main development region, which stretches from the African coast to the Caribbean, and when the SST is warmer than average, about 80 degrees fahrenheit, that indicates a high probability for hurricane activity.
Look to the Pacific
While most hurricanes happen in the Atlantic Ocean, what happens over the Pacific Ocean greatly determines the amount of hurricane activity in a given year. This is because of the El Niño-Southern Oscillation (ENSO), or what people more commonly know as El Niño and La Niña, opposite extremes of environmental conditions happening over the Pacific. These conditions are influenced by a few factors - SST, rainfall, air pressure, and oceanic circulation - with El Niño characterized by warmer-than-average SST and weaker trade winds, and La Niña with cooler temperatures and stronger wind.
In terms of hurricanes, both can have an impact on different regions. When we look at the Atlantic region specifically, La Niña is what concerns climatologists - the westerly winds weaken high in the atmosphere and create greater areas of low vertical wind shear, making it easier for storms to gather strength. On the other hand, El Niño has stronger winds at this level, increasing total wind shear that can tear storms apart before they can develop a healthy circulation.
The Prediction Mix
With these two key factors in place, SST and El Niño and La Niña patterns, climatologists layer in several more ingredients: atmospheric pressure patterns, the strength of the West African Monsoon (which seeds many storms that eventually reach the U.S.), and moisture levels throughout the atmosphere. Climatologists then blend all of this into a model that runs hundreds of simulations with varying starting conditions to map a range of possible outcomes rather than a single prediction.
What This Means for Your Cat Bond
Most hurricane cat bonds are structured as reinsurance triggers, meaning they pay out if losses from a storm or season breach a defined threshold. A forecast calling for an above-normal season with 20+ named storms doesn't automatically mean your bond triggers - but it does reprice risk. Spreads widen, and new issuances get priced more conservatively.
Think of the seasonal forecast as the opening odds. The models are making their best probabilistic bet, and so are you.
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Sources
NASA
FOX Weather
National Oceanic & Atmospheric Administration
Weather.gov