Behind the Forecast: Do hotter oceans mean stronger hurricanes

LOUISVILLE, Ky. (WAVE) - We’re smack in the middle of hurricane season and storms like Dorian continue to dominate headlines.

The Atlantic hurricane season lasts from June 1st through November 30th with the peak around September 10th. However, storms can form outside of hurricane season.

For a hurricane to form, warm moisture rises and condenses into clouds which eventually become thunderstorms. Eventually, an area of low-pressure forms as wind rotates in the atmosphere. For a hurricane to form the following is needed: a preexisting weather disturbance, low wind shear (change in wind speed or direction over a particular distance), sea surface temperatures at least 80° over a depth of 150 feet and an area thunderstorms.

(Business Insider/National Hurricane Center)

Once wind speeds reach 74 mph the storm is officially a Category 1 hurricane on the Saffir-Simpson scale.

Over the past 100 years, global average sea temperatures have risen by just shy of 2°F. While that doesn’t seem like much it can have significant impacts on the strength of hurricanes.

As sea surface temperatures rise, due to climate change or otherwise, the ocean provides more fuel for hurricanes meaning we could see stronger storms. 2018 was the hottest year on record for the planet’s oceans. Our oceans absorb 93% of the extra heat that greenhouse gases trap in our atmosphere. A one degree Fahrenheit rise in ocean temperature can increase a hurricane’s wind speed by 15 to 20 miles per hour, according to Florida State University professor James Elsner. With warmer water, storms are also able to strengthen significantly in small amounts of time. The number of tropical storms that rapidly develop into devastating hurricanes has tripled over the past 3 decades, according to a 2018 study. Another study found that storms reach Category 3 strength almost nine hours faster now than they did in the 1980s, according to NASA.

In addition to the stronger storms, we’re starting to see slower hurricanes. A 2018 study found that hurricanes and tropical storms have been moving 10% slower over the past 70 years. Slower speeds mean more time for a storm to ravage an area with tremendous winds and heavy rain just like we saw in the Bahamas with Hurricane Dorian.

Couple higher sea levels with this and there are even more threats. High seas mean more damaging storm surges during tropical systems. A hurricane's winds blowing directly onshore while during high tide can increase water levels as quickly as a few feet per minute.

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Recent research suggests that wind shear across the Atlantic Basin could increase by 1 to 2 miles per hour for each degree that global temperatures increase. An increase in winds could easily rip apart storms that try to form. So there remains a dichotomy: while the number of tropical systems may remain stagnant or even decrease, the storms that do develop could become stronger. A 2010 article showed that the frequency of storms may decrease between six to 34 percent by 2100 but the intensity of these cyclones could increase by two to 11 percent.

Something else to note is what happens after the strong storms wane. A hurricane removes heat from the oceans rather quickly. The cooler ocean water left behind does not provide enough energy for a new storm to feed off of thus potentially decreasing the overall number of storms.

Eight of the 10 costliest hurricanes on record in the United States have occurred since 2004, according to the Center for Climate and Energy Solutions. The strength of the storms isn’t the only factor in the blossoming recovery costs. Center for Climate and Energy Solutions says that the United State’s coastal population increased by 85 million between 1970 and 2010; coastal counties are now about 40% of the United States’ population. Regardless of the strength of storms, more people are now in harm’s way. This is why it is important to have a reliable and accurate source of weather information regardless of where you live.

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