Henri and Ida: Why did one storm weaken and the other strengthen near land?

Tracking the Tropics

EAST PROVIDENCE, R.I. (WPRI) — Southern New England has already seen its fair share of impacts from tropical systems this hurricane season, but none of the storms have been all that intense.

The strongest system to impact our area recently was Tropical Storm Henri, which brought winds of up to 70 mph to localized areas of Rhode Island and southeastern Connecticut, causing power outages and tree damage.

A week later, Hurricane Ida lashed New Orleans and the surrounding area with estimated winds of up to 150 mph, causing widespread flooding, damage, power outages and at least one death.

So while Henri weakened as it made landfall, why did Ida strengthen as it approached?

A key factor is the ocean temperatures offshore, which are much cooler here in New England. As was the case with Henri, the system was a hurricane over the Gulf Stream (an area of warmer water currents that ride up the Eastern seaboard) but it weakened as it moved over cooler waters.

The Gulf of Mexico has water surface temperatures between 80 and 90 degrees Fahrenheit. Storms are fueled by warm water, so Ida had plenty of ammunition to work with to gain strength.

There’s also typically less wind shear in that part of the country, especially compared to New England. In other words, there’s a lack of shifting or converging winds from different directions.

Hurricane Idea was the second-strongest storm on record to impact the state of Louisiana and ranks among the strongest to impact the country as a whole, based on barometric pressure.

Here are some other notable storms and their respective barometric pressures:

Katrina made landfall as a Category 3 hurricane but had a lower pressure of 920 mb, whereas Ida made landfall as a Category 4 storm with a pressure of 929 mb.

Also worth noting, both storms made landfall in the same area on August 29, exactly 16 years apart.

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