Hurricane Hurricane Dorian

[bjdeming]

Those poor people, my heart just breaks for them. I feel so helpless knowing what is happening and other than prayers, there’s not a dang thing we can do to protect them!!

We can help pick up the pieces. The US Coast Guard is in there, per Tribune updates, along with other international assistance, helping critically injured people get to care centers.

I'd never heard of The Mudd before today, and had to look up what it was like in 2015; here it is today.

 

[Casie]

We can help pick up the pieces. The US Coast Guard is in there, per Tribune updates, along with other international assistance, helping critically injured people get to care centers.

I'd never heard of The Mudd before today, and had to look up what it was like in 2015; here it is today.

It is very poor area in Marsh Harbour that is filled with shanties. They had a big fire last year that destroyed a good portion of it.

It

 

[majorhurricane1703]

I was very curious about something and I’m interested to hear what people would have to say about this. Let’s say hypothetically speaking Dorian made landfall in Miami with 185 mph winds and was slow moving. We know it would cause catastrophic damage, but do you think the the damage in Miami would be eerily similar to the kind of damage we saw in Abaco? By this I mean not just houses being completely wiped away, but some high rises falling over or collapsing and basically the entire city looking like an ocean.

 

[KoD]

Looks like another EWRC is occurring.






It's crazy to see a monster hurricane like this stall out over people's homes & towns. It hasn't barely moved at all since yesterday...

 

[akt1985]

Dorian is now down to a Category 3.

 

[Kory]

 

[Kory]

Upwelling and dry air entrainment has really done a number on Dorian. Eyewall looks open on the west/southwest side looking at radar.

 

[bjdeming]

It is very poor area in Marsh Harbour that is filled with shanties. They had a big fire last year that destroyed a good portion of it.

Well, not "good," of course, but it gives me some perspective. The Mudd was much less populated pre-Dorian. Thanks -- that contrast with 2015 shook me up some.

 

[bjdeming]

Wow. My heart goes out to those people.

This also really underlines what people are saying about the flooding risk as Dorian finally moves northward -- even if it stays off shore all the way (not guaranteed), water from rainfall as well as coastal surge will have a huge impact all the way.

 

[Gail]

Yikes.

 

[Kory]

Yeah, Josh is on the missing person’s list. I’m sure it’s not completely unusual to have zero contact via internet or cell after this kind of disaster but it isn’t good when the shelter he was located at “failed.”

 

[Kory]

Yeah, the eyewall is even more ragged now. Its gonna take a while for Dorian to mix that out...if it does.

Check out the soundings from over Florida and all the dry air in the mid/upper levels (indicated by the large separation in the red and green line)

Miami:

Jacksonville:

This is all being advected into the system via some light to moderate westerly shear.

 

[Evan]

Yeah, the eyewall is even more ragged now. Its gonna take a while for Dorian to mix that out...if it does.

Check out the soundings from over Florida and all the dry air in the mid/upper levels (indicated by the large separation in the red and green line)

Miami:

Jacksonville:

This is all being advected into the system via some light to moderate westerly shear.

Yep. Dorian has really struggled over the past 12+ hours. Hope he continues to do so and is unable to re-organize.

 

[Evan]

Yeah, Josh is on the missing person’s list. I’m sure it’s not completely unusual to have zero contact via internet or cell after this kind of disaster but it isn’t good when the shelter he was located at “failed.”

I was under the impression he had a satellite phone or other way of communicating outside of just a cell phone. Odd that he hasn't yet checked in with anyone, but there could be a reasonable explanation for that.

 

[Timhsv]

I have never really heard as to why does a Hurricane expand in size as it weakens? Anyone?

 

[Evan]

Kory, that is absolutely incredible. It's what you would expect after Dorian stalled out over Grand Bahama, but actually seeing it visually depicted in some way is just jaw-dropping.

 

[Kory]

I have never really heard as to why does a Hurricane expand in size as it weakens? Anyone?

Expansion and/or weakening of the pressure gradient is what causes cyclones to deteriorate. What causes the expansion of the gradient could be dry air, wind shear, or resulting lower pressures from incoming troughs, etc.

Katrina for example had her whole western/southern eyewall collapse due to dry air intrusion. Despite making landfall as a strong category 3 quickly coming down from a 5, that was the widest her wind field ever was was AFTER initial Louisiana landfall due to weakening/expansion of the gradient from disruption of concentric convection around a deep low pressure system. Think of it as a feedback loop as convection gets stronger you have greater rising air from that strengthening convection, and as that airreaches the top of the atmosphere, it sinks around the outside of the storm creating subsidence in essence creating an upper level anti-cyclone or mini-high pressure. But some of that air sinks in the center of the low pressure clearing out an eye. Until that is disrupted for whatever reason, the wind field/gradient will remain tightly wound which causes intensification. When that closed off ring of convection is disrupted, the pressure gradient weakens due to resulting downdrafts from the weakening convection...i.e., expansion of the pressure gradient.

Same goes for Hurricane Gustav in 2008 as did Hurricane Katrina....dry air intrusion weakened the inner core but winds expanded. Sorry for all of the Louisiana examples, they are the ones I am most familiar with.

 

[Evan]

I have never really heard as to why does a Hurricane expand in size as it weakens? Anyone?

I don't know that all hurricanes expand in size as they weaken, but it is extremely common. The eventual outcome is simple enough to explain: it's a transfer of kinetic energy across a greater surface area allowing the energy to be dissipated over a broader area. One common reason for a hurricane to expand in size as it weakens is an EWRC. The process behind that is probably a little too complex to get into in this thread.

Edit: I see Kory has covered a number of detailed reasons for why a hurricane's size might increase as it weakens. I like that his explanation gives a meteorological explanation of the processes that impact storm size in response to Tim's question.

The shortest answer is that it all has to do with physics. You have latent heat in the ocean's water, and that is a form of energy just laying around ready to be used. A hurricane readily uses that heat energy and transfers it into its own system. That heat energy fuels the hurricane. A hurricane is basically a giant heat transfer machine. Just remember that the energy has to "go somewhere" (be dissipated) as the hurricane weakens. Mass and energy have an equivalence. Remember Einstein's famous E=mc^2 equation?

Broadly speaking, a hurricane can dissipate the energy it has in a number of ways. If a storm gets larger as it weakens then it is dispersing its energy over a broader area versus something like a tight eyewall of very strong winds. A larger storm and a smaller storm can be directly compared. Imagine a very small yet strong hurricane with 130mph winds in its eyewall. It may have a similar amount of energy to a much larger hurricane that only has winds of 85mph. The larger hurricane will have a much larger wind-field, but it's peak winds will be less than that of the smaller storm. The example I'm using here assumes that both hurricanes have the same amount of potential energy and it overly simplistic. It's not a binary outcome where you can only have a large storm with broader wind-fields and lower eyewall winds or a storm with smaller wind-fields and more intense eyewall winds. You can absolutely have a storm that has both. The structure of a hurricane is only one part of understanding how it is transferring energy.

Highly recommend you read this blog post. They discuss a number of recent hurricanes, their size, structure, and how much energy they contained. What's really interesting is that they discuss a small and intense hurricane with strong eyewall winds, a much larger hurricane with a much broader wind-field but much lower eyewall winds, and then they also discuss a hurricane that had eyewall winds almost as strong as the smaller and more intense hurricane yet it also has a broader wind-field like a larger Hurricane. .

This is a rather complicated topic, so I'm simply trying to provide a very crude explanation to try to answer your question.

Here's a scientific paper that discusses some of the ways energy is transferred (or transformed) in a hurricane, what that means, what it does, etc.

We're actually still learning a ton about hurricanes. There is still plenty that we don't know. One of the reasons why we know hear a lot more about a hurricane's energy is because our understanding of the physics behind hurricanes has continued to mature. That, and Hurricane Ike really surprised a number of people, and that led to a deeper exploration of how to measure the amount of energy in a storm, the ways that energy might be transferred during the hurricane's lifecycle, and how that impacts we humans and our property and land.

 

[Timhsv]

I don't know that all hurricanes expand in size as they weaken, but it is extremely common. The eventual outcome is simple enough to explain: it's a transfer of kinetic energy across a greater surface area allowing the energy to be dissipated over a broader area. One common reason for a hurricane to expand in size as it weakens is an EWRC. The process behind that is probably a little too complex to get into in this thread. Edit: I see Kory has covered a number of detailed reasons for why a hurricane's size might increase as it weakens.

But to answer your question, the shortest answer is that it all has to do with physics. You have latent heat in the ocean's water, and that is a form of energy just laying around ready to be used. A hurricane readily uses that heat energy and transfers it into its own system. That heat energy fuels the hurricane. A hurricane is basically a giant heat transfer machine. Just remember that the energy has to "go somewhere" (be dissipated) as the hurricane weakens. Mass and energy have an equivalence. Remember Einstein's famous E=mc^2 equation?

Broadly speaking, a hurricane can dissipate the energy it has in a number of ways. A larger storm and a smaller storm can be directly compared. Imagine a very small yet very intense hurricane. It may have a similar amount of energy to a much larger hurricane that only has winds of 85mph.

This is a rather complicated topic, so I'm simply trying to provide a very crude explanation to try to answer your question.

Here's a scientific paper that discusses some of the ways energy is transferred (or transformed) in a hurricane, what that means, what it does, etc.

We're actually still learning a ton about hurricanes. There is still plenty that we don't know. One of the reasons why we know hear a lot more about a hurricane's energy is because our understanding of the physics behind hurricanes has continued to mature. That, and Hurricane Ike really surprised a number of people, and that led to a deeper exploration of how to measure the amount of energy in a storm, the ways that energy might be transferred during the hurricane's lifecycle, and how that impacts we humans and our property and land.

Thanks for that Evan!

 

[Timhsv]

Expansion and/or weakening of the pressure gradient is what causes cyclones to deteriorate. What causes the expansion of the gradient could be dry air, wind shear, or resulting lower pressures from incoming troughs, etc.

Katrina for example had her whole western/southern eyewall collapse due to dry air intrusion. Despite making landfall as a strong category 3 quickly coming down from a 5, that was the widest her wind field ever was was AFTER initial Louisiana landfall due to weakening/expansion of the gradient from disruption of concentric convection around a deep low pressure system. Think of it as a feedback loop as convection gets stronger you have greater rising air from that strengthening convection, and as that airreaches the top of the atmosphere, it sinks around the outside of the storm creating subsidence in essence creating an upper level anti-cyclone or mini-high pressure. But some of that air sinks in the center of the low pressure clearing out an eye. Until that is disrupted for whatever reason, the wind field/gradient will remain tightly wound which causes intensification. When that closed off ring of convection is disrupted, the pressure gradient weakens due to resulting downdrafts from the weakening convection...i.e., expansion of the pressure gradient.

Same goes for Hurricane Gustav in 2008 as did Hurricane Katrina....dry air intrusion weakened the inner core but winds expanded. Sorry for all of the Louisiana examples, they are the ones I am most familiar with.

Thanks for that Kory!