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General Discussion >> Hurricane Ask/Tell

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cieldumortModerator
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Inland Intensification of Tropical Cyclones
      #82377 - Tue Aug 19 2008 08:24 PM

Fay makes for a perfect case example of how little sea surface temperatures can mean. For all the talk about how big and bad any given tropical cyclone is going to get because it's about to go over some vast, nasty eddy of sweltering warm ocean heat content, the truth of the matter is, when it comes to tropical cyclones, sea surface temps, and in some rare cases, indeed, sea surface itself, is not the be all and end all. Far from it.

For the most part, and contrary to popular belief, in order for tropical cyclogenesis to occur, a disturbance requires sea surface temperatures at or above only 20 degrees Celsius. However, the lower range rarely cuts it, and indeed SSTs at or above 26.5 degrees C are usually required. But, in the end, there is really no "magical" number.

Also contrary to another popular myth, as alluded to in the paragraphs above, very hot sea surface temperatures on their own do not make for tenacious hurricanes, or even particularly strong hurricanes.

What both of these facts tell us is that there have to be other, even more critical, players involved. And there are. Tropical cyclones do not exist in the ocean. They exist in the air, and only glide across the oceans (and land). So, as logic would have it, these other, critical players, also exist in the atmosphere; not in the ocean.

Fay strengthened inland for several reasons. The most likely are:

1) Outflow. Fay's outflow in all quadrants improved radically going into and after landfall. This upper-level vacating of air from the surface-up allowed her thunderstorms to evacuate very efficiently aloft, and strengthen mightily. In turn, more air rushed in at the surface, and exited aloft.

This process lowers the pressure inside a cyclone, and no surprise, Fay went from 1003mb or so at 11AM Monday, down to 986mb (often associated with Cat 1 hurricanes!) by the same time today.

2) Lack of friction. Florida is a very flat state. Unlike most landfall locations, there simply aren't many, if any, hills and valleys and other obstacles that usually work to gnaw away at a tropical cyclone's windflow..

3) Moisture content. Fay was always wrapped in a fairly moist envelope. Having been born from within a water vapor balloon that was her mid-level circulation and associated upper-level anticyclone, most of this fetch of deep, tropical air followed her everywhere she went. Then, upon entering Florida, Fay was greeted by yet more warm, moist atmosphere - even the ground was frequently like traveling over a very warm, shallow ocean.

4) Momentum. Fay was intensifying rather impressively right into landfall.

These kinds of events are not unprecedented. However, they are rare. Most recently, there was a lot of debate as to whether or not time should have been added to Tropical Storm Erin (2007), as when she entered Oklahoma, there for about six hours, Erin saw a very substantial pressure fall, along with sustained winds of at least minimal tropical storm force over a sizable area, widespread, deadly torrential rains, gusts fully at hurricane-force, and even an eye-like feature visible on radar and a little bit on IR channels.

I have included the image of Erin's track below (Green designates Depression. Yellow, Storm)


And here is what Erin looked like while over central Oklahoma


Read more about Erin's wacky inland resurrection here, and here, and here (NHC) PDF.


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StrmTrckrMiami
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Re: Hurricane Watches up for North Florida, Georgia as Tropical Storm Fay Moves North Northeast [Re: cieldumort]
      #82406 - Tue Aug 19 2008 09:47 PM

Okay, I have been gone for the last few hours and have come up with a few questions myself in regards to Tropical Storm Fay. Anyone can answer them, I just would like them confirmed.

1. Why is Fay Stationary? She is in the same exact place she was when I left at around 6:30pm EST. Is there a meteorological reason she is not going anywhere?

2. There has been some talk about Fay coming back toward us. What does this mean? Why would a Tropical Storm come back the way it entered? In this case, would she be much severe?

3. What are the chances of fay sticking around and the other Invest catching up to her? I know this sounds stupid on my part and all, but what is the likelihood of this happening?

4. Why are all of the weather plots just throwing Fay all over the place? Where does the NHC, UKMET and other data plotters or what ever you call them get their data from? How do they predict where the storm will be? Why are they changing so sporadically?

Lastly, what is Fay's overall plans? Things look like she is trying to strengthen but is having trouble doing so. She is defiantly one of my weirdest storms I've ever tracked, and quite interesting for my first storm. I have another thought on my mind. Why is is still Windy in Fort Myers? Were getting the same tropical conditions we have been getting all day. Wind Gusts are the same as they were when Fay was here. The rain has stopped since the sun went down. Any probable reasons for all of this?

(at this rate, I am going to expect the unexpected with Fay. She seems to be one of the wildest storms anyone has seen, and tracked. After all, she did strengthen over land, as well as form an eye that was visible on satellite imagery over land as well. I think I'm safe to say that no one is quite sure what to expect with Fay. Am I right in saying this?)

Thats it for now. I suppose.

--------------------


Tracking Storms Since 2004
Miami, Cocoa, Fort Myers and Jacksonville
Currently Reside in New England


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cieldumortModerator
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Re: Hurricane Watches up for North Florida, Georgia as Tropical Storm Fay Moves North Northeast [Re: StrmTrckrMiami]
      #82427 - Wed Aug 20 2008 12:32 AM

1. Why is Fay Stationary? She is in the same exact place she was when I left at around 6:30pm EST. Is there a meteorological reason she is not going anywhere?

Fay is not *really* stationary. She is moving to the NNE at around 3-4 mph, over all. The reason tropical cyclones may slow down or stall is almost always because steering currents become light, conflicting, or virtually non-existent, for a spell. Fay may be heading a touch east of NNE, now.

2. There has been some talk about Fay coming back toward us. What does this mean? Why would a Tropical Storm come back the way it entered? In this case, would she be much severe?

Fay is not likely to come back exactly the way she entered.
The reason for the course correction has to do with steering currents, which are now going to be blowing from the east-northeast ,east, and east-southeast, instead of out of the south, and southwest.
She may or may not be any more intense. A lot of this depends on whether or not she spends any time back out over water.

3. What are the chances of fay sticking around and the other Invest catching up to her? I know this sounds stupid on my part and all, but what is the likelihood of this happening?

In most cases, the odds would be very low. In this particular case, it is in the realm of possibilities.

4. Why are all of the weather plots just throwing Fay all over the place? Where does the NHC, UKMET and other data plotters or what ever you call them get their data from? How do they predict where the storm will be? Why are they changing so sporadically?

The NHC is not a model. NHC stands for National Hurricane Center, which is the public tropical foresting arm of the National Weather Service.

The NHC creates their own plots, using a blend of models weighted for accuracy and human forecaster experience.

UKMET is a model. UKMET stands for United Kingdom Meteorological, from where the run comes.

For the most part, with models, computers dissect the data that is fed into them, and using a certain degree of AI, are able to create tracks and intensities of tropical cyclones within a range of probabilities that sometimes make them useful.

Lastly, what is Fay's overall plans? Things look like she is trying to strengthen but is having trouble doing so. She is defiantly one of my weirdest storms I've ever tracked, and quite interesting for my first storm. I have another thought on my mind. Why is is still Windy in Fort Myers? Were getting the same tropical conditions we have been getting all day. Wind Gusts are the same as they were when Fay was here. The rain has stopped since the sun went down. Any probable reasons for all of this?

Fay doesn't have "plans," as much as "plans" will be made *for* Fay.

She is a very weird storm, indeed. Pretty fascinating. I'm sure many a thesis will be conjured up after this week.

Fay's windfield is pretty broad, and she did not weaken at all most of the day.

As for the rain stopping since the sun went down, I doubt that there is any significant connection. More probably, this is because you are now on the subsident side of the cyclone, with drier winds coming in out of the northwest, while at the same time Fay herself has passed well to your east.


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JMII
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Re: Inland Intensification of Tropical Cyclones [Re: cieldumort]
      #82455 - Wed Aug 20 2008 09:10 AM

Thanks for the info on Erin.

I've always written off storms as soon as they got over land since I assumed that once cut-off from their energy source (warm ocean waters) that would slowly spin down and die. However given the right conditions its clearly possible a storm can not only survive but thrive (for short periods atleast) while over land. I think Fay will become one of those storms that gets studied in detailed in attempts to figure out just which parameters in the astmosphere are needed to keep a storm going.

--------------------
South FL Native... experienced many tropical systems, but actually had to put up the panels for:
David ('79) - Floyd ('87) - Andrew ('92) - Georges ('98) - Frances ('04) - Wilma ('05) - Matthew ('16) - Irma ('17)


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cieldumortModerator
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Re: Inland Intensification of Tropical Cyclones [Re: JMII]
      #82525 - Wed Aug 20 2008 05:38 PM

Writing off a tropical cyclone simply because it has moved inland is one of the big mistakes people do. Sure, most of the time things go as expected. But sometimes, and not all that infrequently, really, inland TCs at the very least unleash all of their rainfall potential over a very concentrated area by a process which results in core rains. At other times, although pretty rare, they can even intensify over land, as Fay did. In either case, the results can be exceptional, and catch many people who let their guard down, totally off guard.

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Ed DunhamAdministrator
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Re: Inland Intensification of Tropical Cyclones [Re: cieldumort]
      #82812 - Sat Aug 23 2008 11:40 PM

cieldumort has touched on the primary reason, i.e., Fay was intensifying just before landfall and continued this process after landfall, but one other factor also must be considered. When the water table in the Everglades is high - and warm - storms can maintain intensity while going across the southern half of the Florida peninsula. A good recent example of this is Hurricane Irene in 1999.
ED


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Lamar-Plant City
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Re: Inland Intensification of Tropical Cyclones [Re: cieldumort]
      #82815 - Sun Aug 24 2008 08:36 AM

Quote:

Writing off a tropical cyclone simply because it has moved inland is one of the big mistakes people do. Sure, most of the time things go as expected. But sometimes, and not all that infrequently, really, inland TCs at the very least unleash all of their rainfall potential over a very concentrated area by a process which results in core rains. At other times, although pretty rare, they can even intensify over land, as Fay did. In either case, the results can be exceptional, and catch many people who let their guard down, totally off guard.



This is exactly what happened in Polk County Florida for Hurricane Charlie. My parents live there and the forcast was for it to only have 60mph wind by the time it reached them (just north of Lake Wales). I had called them as the storm turned towards them and mom repeated the prediction and said not to worry becuase it would be so weak by the time it got to them. They really didn't prepare at all for the 125mph winds that came across the lake at them and nearly destroyed their house. Same story all the way to Orlando and just east. NHC needs to get a better handle on this phenomenon to adequately warn folks and not give them a false sense of security just because the storm is INLAND.

--------------------
If you don't like the weather, wait 5 minutes...
2017 Season Prediction: 16/7/3


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mcgowanmc
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Re: Inland Intensification of Tropical Cyclones [Re: Lamar-Plant City]
      #82816 - Sun Aug 24 2008 09:17 AM

Good Morning!

Last nite I posted that Fay was gone.
Meaning it had gone extra tropical. And I was sleep deprived-;}

The NHC has Fay just now moving into Alabama this AM.

It's like the General has sent her Army away while she continues the march to New Orleans.
And saying that she will be their for 72 hours before marching into Mississippi.

I've said this many times-Fay's the weirdest storm I've ever seen.
She could come back and dump 26 inches of rain on top of the Superdome and I wouldn't be surprised.

I'd love to be in NO right now, to feel the conditions:

http://euler.atmos.colostate.edu/~vigh/guidance/northatlantic/track_late1.png


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LoisCane
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Re: Inland Intensification of Tropical Cyclones [Re: mcgowanmc]
      #82817 - Sun Aug 24 2008 09:53 AM

After tracking Danny all the way across the SE and back into water I've learned never to write off a storm once it has hit land.

In Fay's case she may move back over water again but for now the big story remains all the water she is dumping on the Deep South.

Wanted to add also that interaction with land does not always kill off a Tropical Cyclone and Georges was another system that had a penchant for hitting land and kept going. He hit every piece of land he could and was still viable
when he bashed his way through Key West and the Lower Keys.

It's wrong to simply say Haiti will tear apart a storm or that once over land with weak steering currents a storm will be gone.

Personally, I think Fay will fade away and dump legendary amounts of rainfall over the SE.

But, she should be a big lesson on this problem. And, I believe traveling across South Florida didn't do much to
break up Betsy or Andrew as they both barreled on towards landfall in Louisiana. In fact if I remember on the news they kept mentioning how if anything Betsy was still intensifying while her northern half was over South Florida. I could be wrong but there was discussion even then how South Florida's flat landscape and the Everglades does nothing to interfere too much with intensity after the initial landfall. And, the Yucatan is another flat spot where storms don't break up the moment they hit land.

--------------------
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