Question Box:

[rainbird]

Think this post is great!! - especially when we are entering into a new hurricane season - Need an answer to a question please - very elementary one - What is the LLC?? - Thank you much -

[wjs3]

Glad you enjoy it. I enjoy it too. I think it's one of the great things about this board.

LLC is a Low Level Center (or Low level Circulation). Key to identifying a tropical cyclone is identifying a surface low pressure system. (you may have read a LOT about this with 91L today). We need to see a closed low pressure system in order to have a TC.

Often in developing TCs, we'll see multiple LLCs (Alberto, for instance) and one "takes over". You'll also see a lot of discussion on the boards about whether (in a satellite image) we are looking at a LLC, a MLC (Mid Level circ) or even an upper Low.

The LLC is what matters in calling a TC a TC, and there are only a few ways to identify it...

-Wind sat imagery, like quickscat
-Surface observations (usually from buoys, sometimes from land-based)
-Recon
-Visible satellite imagery where we can see the low level (cumulus) field

Great question!

WJS3

[Rieyeuxs]

I still han't got a handle on what makes an official "Invest". I understand it's an area of interest, but I've seen a lot of argueing over what and when a particular feature should be "Invested". Is there an official set of criteria?

[Cyclenall]

If anyone wants the answer to this question, I have it now:

Question: What Tropical Cyclone had the largest eye ever seen?

Answer: Typhoon Carmen of the Western Pacific in 1960 had the largest eye with it being 200-nm (370 km).

Does anyone have a picture of Typhoon Carman? Remember it is 1960 so it would be super old.

[Audrey2Katrina]

The only satellite that MIGHT have been up... although I know the early images I've seen, from that time would've been TIROS images... perhaps you could do a Google image search; but I doubt you'll find anything of quality back then, and if it was in the WPAC, I'd like to know the documentation for a 200nm eye (which would be around 220+ statute miles) seem rather beyond the realm of plausible, but I claim to be no expert on the matter; particularly not in the WPAC... I just find those numbers a tad on the incredulous side.

A2K

[AJC3]

The only satellite that MIGHT have been up... although I know the early images I've seen, from that time would've been TIROS images... perhaps you could do a Google image search; but I doubt you'll find anything of quality back then, and if it was in the WPAC, I'd like to know the documentation for a 200nm eye (which would be around 220+ statute miles) seem rather beyond the realm of plausible, but I claim to be no expert on the matter; particularly not in the WPAC... I just find those numbers a tad on the incredulous side.

A2K

Measured by the Kadena AFB Radar on Okinawa. I think there may be an image of it floating around on the web somewhere but I haven't been able to find it yet.

Bingo...you can find it here...

http://www.npmoc.navy.mil/jtwc/atcr/196 ... wnp/31.pdf

[Audrey2Katrina]

Well I guess I stand corrected... sort of.. LOL. From that radar pic she looked all "eye"... with a few spotty openings... perhaps why the report frequently describes the eye as "ill defined"... doubtless there was a mass of clouds further out--too bad we didn't have any good resolution satellites back then. She certainly wasn't much with regard to winds though, was she? I mean top winds I saw skimming through there were only above 70 KT on one reading, all the rest pretty much below, and I guess her "eye" oggled all over the place. Though perhaps for a short while they were above that typhoon threshhold. Wish I could make out a mileage scale on that radar pic... because I have no idea what it indicates scale wise... but the report clearly does say that the wall-clouds were of that diameter albeit in what would appear to be statute miles--still enormous--kind'a makes her have an extraordinary wind field doesn't it? I mean the TS winds wouldn't even "begin" till 200 miles out from the COC! Something to give the idea of "size" being defined as extend of TS winds from COC a whole new context as well.

Thanks for the link AJC3.... enjoyed the read--very interesting.

A2K

[Cyclenall]

Well I guess I stand corrected... sort of.. LOL. From that radar pic she looked all "eye"... with a few spotty openings... perhaps why the report frequently describes the eye as "ill defined"... doubtless there was a mass of clouds further out--too bad we didn't have any good resolution satellites back then. She certainly wasn't much with regard to winds though, was she? I mean top winds I saw skimming through there were only above 70 KT on one reading, all the rest pretty much below, and I guess her "eye" oggled all over the place. Though perhaps for a short while they were above that typhoon threshhold. Wish I could make out a mileage scale on that radar pic... because I have no idea what it indicates scale wise... but the report clearly does say that the wall-clouds were of that diameter albeit in what would appear to be statute miles--still enormous--kind'a makes her have an extraordinary wind field doesn't it? I mean the TS winds wouldn't even "begin" till 200 miles out from the COC! Something to give the idea of "size" being defined as extend of TS winds from COC a whole new context as well.

Thanks for the link AJC3.... enjoyed the read--very interesting.

A2K

If you want more pictures look in the topic I posted in. It's the one about "any hurricane pic here" type topic. It's real, and out of this world.

[Audrey2Katrina]

I'll have to do that, Cyclenall... Thanks....

A2K

[Audrey2Katrina]

Someone want to give Rieyeuxs a hand with that "Invest" question? I'd try but I feel some of the other more experienced would do it better than I.

A2K

[weatherbee1982]

Since I haven't seen it asked here, I'll pose a conceptual issue that's had me wondering:

How can pressure be both low and high at different layers of the atmosphere?

Since pressure is the weight of the atmosphere above a given location, it would seem to be naturally lower at increasing height. But we often speak of low pressure at the surface and high pressure above, or an upper-level low over a surface high.

Is it all relative? That is, a "high" can be above a "low" because of pools or layers of different air density -- pools that don't match what a straight linear pressure change going upward would produce?

Hope that's at least an understandable question.

To answer this question, it comes down to a matter of convergence and divergence. When you have an upper level high (low) pressure system, you have created an area within the upper layers which are divergent (convergent). As a result, you must compensate for this loss (gain) of atmosphere by taking (displacing) atmosphere from the lower levels. As this process takes hold, you have an upward (downward) motion beneath the high (low) pressure aloft, which eventually makes it to the surface. Upon making it to the surface, the surface pressure decreases (increases) as a result of the loss (gain) of atmosphere to/from higher levels, thus you form an area of convergence (divergence), as well as an area of low pressure (high pressure).

Hope that provides an explanation as to how you can have different pressures at different levels.

[wjs3]

I still han't got a handle on what makes an official "Invest". I understand it's an area of interest, but I've seen a lot of argueing over what and when a particular feature should be "Invested". Is there an official set of criteria?

Well, first, an invest is when we see a lot of relevant info come up on a potentially developing system on the NRL site:

http://www.nrlmry.navy.mil/tc_pages/tc_home.html

As I've always understood it, the NHC (or JTWC, etc) "opens a window" when they think a disturbance merits having all the info from the many sensors in one place. That I know of, there are no formal criteria for an invest. But I am not an expert on NHC operations.

However, the reason you see it discussed so much around here is that we watch the tropics pretty intensely, and some people have strong opinions about when a system has potential and an invest should be opened. Sometimes this differs from what the pros think.

Importantly, once a system becomes an invest, we begin to see some model runs and results (track and intensity) for it.

Take these early runs with a great, great big grain of salt. Without a well defined center of circulation (which usually makes it a TD, not an invest), the model runs we'll see can be pretty squirrelly.

WJS3

[wjs3]

Recurve wrote:
Since I haven't seen it asked here, I'll pose a conceptual issue that's had me wondering:

How can pressure be both low and high at different layers of the atmosphere?

Since pressure is the weight of the atmosphere above a given location, it would seem to be naturally lower at increasing height. But we often speak of low pressure at the surface and high pressure above, or an upper-level low over a surface high.

Is it all relative? That is, a "high" can be above a "low" because of pools or layers of different air density -- pools that don't match what a straight linear pressure change going upward would produce?

Hope that's at least an understandable question.


To answer this question, it comes down to a matter of convergence and divergence. When you have an upper level high (low) pressure system, you have created an area within the upper layers which are divergent (convergent). As a result, you must compensate for this loss (gain) of atmosphere by taking (displacing) atmosphere from the lower levels. As this process takes hold, you have an upward (downward) motion beneath the high (low) pressure aloft, which eventually makes it to the surface. Upon making it to the surface, the surface pressure decreases (increases) as a result of the loss (gain) of atmosphere to/from higher levels, thus you form an area of convergence (divergence), as well as an area of low pressure (high pressure).

Hope that provides an explanation as to how you can have different pressures at different levels.

Thanks for the great answer. It ried to avoid the issue of divergence/convergence because (1) I couldn;t figure out a way to talk about it succinctly, like you did and (2) I was worried about raising the more complex issue of sources for divergence in a tropical vs extratropical system.

But in rereading, your explanation is better...it's hard to talk about this without talking about convergence and divergence.

WJS3

[Cyclenall]

I have a few questions to ask:

1. What Hurricane in either the Atlantic or East Pacific ocean maintained it's category 5 strength the longest?

2. What causes a "winter pattern" in the Atlantic ocean during the winter months of the tropics? There are no tropical waves, no blobs, ect. It seems so different and what are the shear levels at that time and why are they like that during that time?

3. What year had the highest sea surface temps in the Atlantic ocean overall?

[Cyclenall]

Bumb

[Matt-hurricanewatcher]

I have a few questions to ask:

1. What Hurricane in either the Atlantic or East Pacific ocean maintained it's category 5 strength the longest?

2. What causes a "winter pattern" in the Atlantic ocean during the winter months of the tropics? There are no tropical waves, no blobs, ect. It seems so different and what are the shear levels at that time and why are they like that during that time?

3. What year had the highest sea surface temps in the Atlantic ocean overall?

Hurricane Allen 1980 lasted the longest as a major, then Ivan. I would have to look up what lasted the longest as a cat5. I think Ivan is pretty close.

See are planet is at 23.5 degrees tilt. Which when the winter comes the earth northern hem is facing away from the sun. In which the north pole(South pole in there winter)has little or no sun. What happens the northern area's get colder while the equator doe's not get any cold=a wider temperature spread between 0 and 60 north.

This causes the two air masses cold to the north and warm to the south to form a zone called the polar front/jet stream.

Also the wind patterns are high pressure near 30 north/south. Which is air that sinks. This sinking air then flows back into the equator in both from the north and south of it, then it rises up into what you call the ITCZ. In which is a zone of rising air. Then this rising air turns northward again when it hits the tropause around 12 miles around the equator. Which starts it over again. This is called a hadley cell.

Then on the northern side of this area of high pressure or sinking air is called the westly. Which is another zone of rising air.

Also the earth moves over 1,000 mph at the equator. While the poles move only a few feet. Which makes the winds/air move to the right. So that is why the air patterns/jet streams move west to east. In that is why extratropical/low pressure area's move counter-clockwise on this side of the planet.

Also at the north and south poles there is a large area of high pressure. Which wiinds then are called the eastly. Which also push up against the air moving northward to cause system to form.

So durning the winter this gets stronger in pushs deeper into the tropics=killing the tropics. Causing shear to get to strong/cooling off sst's.

2005 had the warmest sst's ever recorded for the Atlatnic.

[Cyclenall]

I have a few questions to ask:

1. What Hurricane in either the Atlantic or East Pacific ocean maintained it's category 5 strength the longest?

2. What causes a "winter pattern" in the Atlantic ocean during the winter months of the tropics? There are no tropical waves, no blobs, ect. It seems so different and what are the shear levels at that time and why are they like that during that time?

3. What year had the highest sea surface temps in the Atlantic ocean overall?

Hurricane Allen 1980 lasted the longest as a major, then Ivan. I would have to look up what lasted the longest as a cat5. I think Ivan is pretty close.

See are planet is at 23.5 degrees tilt. Which when the winter comes the earth northern hem is facing away from the sun. In which the north pole(South pole in there winter)has little or no sun. What happens the northern area's get colder while the equator doe's not get any cold=a wider temperature spread between 0 and 60 north.

This causes the two air masses cold to the north and warm to the south to form a zone called the polar front/jet stream.

Also the wind patterns are high pressure near 30 north/south. Which is air that sinks. This sinking air then flows back into the equator in both from the north and south of it, then it rises up into what you call the ITCZ. In which is a zone of rising air. Then this rising air turns northward again when it hits the tropause around 12 miles around the equator. Which starts it over again. This is called a hadley cell.

Then on the northern side of this area of high pressure or sinking air is called the westly. Which is another zone of rising air.

Also the earth moves over 1,000 mph at the equator. While the poles move only a few feet. Which makes the winds/air move to the right. So that is why the air patterns/jet streams move west to east. In that is why extratropical/low pressure area's move counter-clockwise on this side of the planet.

Also at the north and south poles there is a large area of high pressure. Which wiinds then are called the eastly. Which also push up against the air moving northward to cause system to form.

So durning the winter this gets stronger in pushs deeper into the tropics=killing the tropics. Causing shear to get to strong/cooling off sst's.

2005 had the warmest sst's ever recorded for the Atlatnic.

Nice, thanks for all that information. 2005 had the warmest SST's ever recorded? I never knew that but that makes sense either way.

[whereverwx]

Hmm… might be a dumb question (lol), but what was the most normal season on record for the Atlantic basin?

[NYCHurr06]

Hmm… might be a dumb question (lol), but what was the most normal season on record for the Atlantic basin?

Hm...I don't know if you would be able to get a direct answer on that cause the definition of a "normal season" has changed as the seasons have gone on...i.e. what was normal in 1956 might be different now.

But, I am very interested as to see what others have to say.

[whereverwx]

Hmm… might be a dumb question (lol), but what was the most normal season on record for the Atlantic basin?

Hm...I don't know if you would be able to get a direct answer on that cause the definition of a "normal season" has changed as the seasons have gone on...i.e. what was normal in 1956 might be different now.

But, I am very interested as to see what others have to say.

That's true. Data and averages, etc., have changed since we’ve progressed through time, and it will be interesting to see what the others have to say.