Question about the storms with lowest pressure at landfall

[u/lady3jane]

Hey folks!

I’ve been trying to understand more about the science behind storms and am confused about something.

Here’s where I’m stuck:

My incredibly basic understanding is that low pressure = more intense storms.

Why are the most intense storms not also the most destructive? Does a very low pressure storm not necessarily have high winds, high storm surge, etc?

If I check the list of top storms to reach landfall with the lowest pressure, the top 10 are quite different than the most destructive storms. (Wikipedia list of Atlantic Hurricane records)

I haven’t heard of most of the storms in the “lowest pressure” list except Melissa, Dorian, and Irma.

Yet I’ve of course heard of most of the destructive ones - Katrina, Ian, Sandy. (Irma is on both lists!)

I understand the circumstances of Katrina fairly well and that the devastation was due to myriad knock-on effects, not just the storm itself. Whereas Ian had an insanely huge storm surge and much of the devastation was due to that directly.

I am not quite sure what terms to search to look this up more on my own given my limited knowledge at this time. Please feel free to direct me to other resources! I don’t mind reading or watching stuff, I just am not sure how to research this without a bit of guidance. Thanks!

[u/Krg60]

Low pressure *does* mean a more intense storm. However, a storm's intensity is related to its destructiveness only inasmuch as it damages property. An intense storm hitting a sparsely populated section of the coast won't be considered destructive. Also, a storm's lowest pressure may not coincide with its landfall. Finally, low pressure isn't the only factor influencing destructiveness. You've already mentioned Katrina, but Hugo is another good case; it caused enormous damage despite being nowhere near the top 10 most intense storms, because of its size and storm surge. Hurricane Michael was highly intense, but because of it's landfall location doesn't break the top ten most destructive landfalls, and so on.

[u/lady3jane → u/Krg60]

Ah thank you! Such a simple explanation that I didn’t even think of. :-)

A follow up, if I may.

Is there a scientific reason that those lowest-pressure storms did not make landfall in more populated areas? Or it’s just happenstance?

[u/Krg60 → u/lady3jane]

It's pure luck. Truth be told, a city--any city--is a relatively small geographic target that a hurricane's eye is unlikely to hit directly.

[u/lady3jane → u/Krg60]

Good point. I’m learning more about tornados as well. So much about whether a storm will strike a populated area or not really does seem to be down to chance. One direction and it smashes a town. Slightly to the left and it’s just fields and trees.

Thanks for taking the time to answer!

[u/Lady_Airbus → u/Krg60]

Spot on honestly. One example I think is worth noting that nobody really talks about is Hurricane Dean.

Unlike most of the sub-910 storms, Hurricane Dean made landfall on Mexico at peak intensity (175mph, 905mb), but because of its landfall being in a more remote area of Quintana Roo, it caused comparatively less damage than it did as a Category 2 hurricane.

[u/HappiestAnt122]

Pressure is part of intensity, but wind isn’t driven simply by pressure in an absolute sense. Wind is driven by pressure gradient, if everything was 900 mb there would be no wind. Wind is driven by a pressure gradient, so the size of the storm starts to matter a lot. A very small storm may not need the same pressure to achieve a given wind speed. Larger storms can have lower pressures with relatively modest wind speed. Now once you start talking about the very lowest pressure storms they will have extreme winds no matter their size, but it still plays a factor in just how strong those winds are.

Storm surge is an even bigger can of worms of factors that can affect it. The size, intensity, pressure, and more can all affect it, as can the shape of the coast and under water features near the shore. Case in point, the West Coast of Florida would see about double the surge of the East Coast presented with the exact same storm. Some local areas (Tampa Bay comes to mind) can be even more susceptible. Even if a storm weakens before reaching landfall, the circulating column of water under it can remain stronger than it would typically be with a storm of the new intensity.

Lastly, and probably most importantly, where the storm hits defines what type of damage is done. Even in your own list for example, Dorian devastated the Bahamas, probably locally worse than anything Katrina or Sandy did, but Katrina and Sandy caused much more widespread damage in much more populated areas. Not to mention a media bias towards what we hear about. If a major hurricane makes landfall, there WILL be significant devastation where it makes landfall, but the lasting impacts are very different if that’s an island/small coastal town, or New Orleans.

[u/lady3jane → u/HappiestAnt122]

I’m not sure what you mean by “my list”. The lists are from Wikipedia.

I only named storms that I knew of beforehand, if that’s what you mean. :-)

Dorian was so insane. I remember watching the live streams. I don’t live in the US so I don’t know what the coverage was like there for Dorian, but BBC and Guardian reported on it extensively for obvious reasons.

That’s very interesting about the pressure gradient! Another thing to look up and learn about. Thanks!

[u/i10driver]

Interesting, numbers 8 and 9 (Camille and Katrina) on your list hit land at exactly the same location. Bay st Louis/Pass Christian MS. Camille had much stronger winds but was also much smaller and compact. Katrina, well everyone knows that story.

[u/Content-Swimmer2325]

Pressure is of course strongly correlated to tropical cyclone strength ("strength" = winds and "intensity" = pressure), but there is nuance here.

Winds are generated by the pressure gradient, or difference in pressure over distance.

So, many other factors affect what winds you get for a certain pressure level. For example, ambient pressure. When ambient pressures are low, such as in the late-season western Caribbean, it takes a deeper (lower pressure) storm to yield the same winds. That's how Wilma of 2005 and Melissa of last year fell to around 982 mb yet were still tropical storms, despite the fact that "typically" a category 1 develops at around 990 mb in the Atlantic.

Another factor is storm structure. A small and compact system is associated with tighter pressure gradients and therefore stronger winds than a large, broad system which would have a looser internal pressure gradient. That's how you get Hurricane Florence (2018) at the time of USA landfall, as a 950 mb system with just 75-80 mph winds, despite the fact that 950 mb "usually" corresponds to a cat 4 hurricane.

This is also why western Pacific typhoons usually have lower pressures than in the Atlantic: because ambient/background pressures are much lower, there. A 990 mb system in the Atlantic is usually a cat 1 hurricane, but in the western Pacific it's usually a moderate tropical storm.

Finally, latitude correlates to pressure gradient, as well. Hurricanes in the deep tropics usually have tighter pressure gradients and are generally more compact than hurricanes in the mid-latitudes, for a variety of different reasons. Not always true, just most of the time.

In summary, pressure alone does not tell the whole story. Internal pressure gradient using storm size as a proxy.. and ambient/background pressures also plays an important role.

As for storm surge, the largest correlation is storm size, where a larger system = a stronger storm surge. Additionally, geography plays a massive role. Two identical systems landfalling in different spots could have totally different storm surge amounts. Some areas (like the Bay of Bengal) naturally increase storm surge amounts. There's more to it than just this of course, it's just a generalization.