ATL: Tropical Depression Fay

[cpdaman]

look at the 3 hour trends on the 500-850 mb maps, there is a bit of an upper level high in the central gulf which appears to have some sort of reflection now at the lower levels (500-850) mb. the steering around this would of course be NW to SE, so perhaps this is why she seems stuck again.

[paintplaye]

Looking at the radar there is some convection trying to get started in the eye.
The center appears to be 29.3 81.1.
Question for the mets.
Why is it that when she was over the ocean the eye got real big but now that she's over land it seems to be getting smaller with more convection toward the center?

Friction-induced low-level convergence over the land.

Could you explain if you have time?

With a synoptic-scale low pressure system, in the absence of friction, the flow around the center of the low will tend to become balanced such that the inward pressure gradient force trying to push the air directly toward the center is exactly counterbalanced by the sum of the Coriolis force and the centrifugal force. This is called gradient wind balance, in which the flow is along isobars and doesn't converge in toward the center. Over water, the friction is low: there is still convergence toward the center, but most of the energy in the wind is in the rotation around the center. However, once a tropical cyclone (or any other large-scale cyclone, for that matter) moves from over water to over land, suddenly the friction over the surface becomes a lot greater. Now the winds are no longer in balance, because the pressure gradient force stays the same, while the centrifugal and Coriolis forces weaken. This happens because both the centrifugal and Coriolis forces are dependent on the wind speed. When the cyclone moves over land, increased friction slows the winds down, and the pressure gradient force takes over, pushing the air in closer to the center of the storm (increased convergence). It's the same effect that causes the tea leaves on the bottom of a cup of tea to bunch toward the center when you stir the tea.

Ironically, even though the winds weaken, such friction-induced convergence can actually intensify the storm in the short term, because the air is able to get closer to the center before being balanced by centrifugal force, making the winds near the center stronger, and the increased convergence can enhance thunderstorm formation near the center. The effect is short-lived for a TC, though, because the TC needs the moisture and heat flux from the warm water to keep the warm core near the center, which maintains the pressure gradient. Over land, this becomes almost absent (again, most of the time!) and the low pressure weakens both due to friction retarding the winds and due to the loss of significant moisture flux from the surface.

Sorry if this is too technical, but I wanted to be thorough.[/quote]

Ooo Ok I see. Thank you. So this is what happened when Fay came in the first time?

[Ed Mahmoud]

Slow mover, is all I can tell. Lots of rain.


Winds gusting to tropical storm force at MCO and ORL. Well inland.

I used to live in Orlando, FL 32813 back in 1983 and 1984, not too far from an airport, which I assume is ORL. Lots of time on the OBT. Good times.

Ahm, you know what hangs around OBT don't you? LOL

Only 'gentlemen's bar' I had ever been to with dollar drafts. Even in 1983, that rocked. I was young and foolish then. I'm married now, and despite living in Houston, capital of the world for 'gentlemen's bars', I never go.

Code: Select all

Current Weather Conditions:
ORLANDO EXECUTIVE AIRPORT, FL, United States 
(KORL) 28-33N 081-20W 37M 

--------------------------------------------------------------------------------
 
Conditions at  Aug 21, 2008 - 08:27 PM EDTAug 21, 2008 - 07:27 PM CDTAug 21, 2008 - 06:27 PM MDTAug 21, 2008 - 05:27 PM PDTAug 21, 2008 - 04:27 PM ADTAug 21, 2008 - 03:27 PM HDT
2008.08.22 0027 UTC 
Wind  from the SW (230 degrees) at 23 MPH (20 KT) gusting to 36 MPH (31 KT) 
Visibility  2 1/2 mile(s) 
Sky conditions  overcast 
Weather  Heavy rain
Mist 
Precipitation last hour  0.17 inches 
Temperature  75 F (24 C) 
Dew Point  71 F (22 C) 
Relative Humidity  88% 
Pressure (altimeter)  29.57 in. Hg (1001 hPa) 
ob  KORL 220027Z 23020G31KT 2 1/2SM +RA BR SCT018 BKN026 OVC042 24/22 A2957 RMK AO2 PK WND 23036/0002 P0017


[fasterdisaster]

Once again she looks better on land than over water

Someone needs to remind Fay she's a tropical cyclone, sheesh.

[Wthrman13]

Ooo Ok I see. Thank you. So this is what happened when Fay came in the first time?

It might have been part of it, but I don't think it was the whole explanation. A lot probably had to due with enhanced latent heat (moisture) flux from the Everglades, and the very favorable upper-level divergence over the storm. If I had to hazard a guess, I would say the frictional convergence helped to organize a tight inner core, and the central low pressure was maintained and enhanced by the aforementioned UL divergence.

[Ed Mahmoud]

Houston is in the cone! That means I won't be one of only two or three Texas posters on this thread!

[paintplaye]

Houston is in the cone! That means I won't be one of only two or three Texas posters on this thread!

Yea I am from Houston too. I posted on the KHOU board yesterday and was like OMG HOUSTON IS IN THE CONE! A couple of people I think got freaked out until they looked at the cone haha.

[cpdaman]

quick what way does this appear to be moving, anywhere

http://metofis.rsmas.miami.edu/~dortt/s ... 1_loop.gif

note i'm not sure how much detail one can get from this map, but i think you get the picture

[paintplaye]

Ooo Ok I see. Thank you. So this is what happened when Fay came in the first time?

It might have been part of it, but I don't think it was the whole explanation. A lot probably had to due with enhanced latent heat (moisture) flux from the Everglades, and the very favorable upper-level divergence over the storm. If I had to hazard a guess, I would say the frictional convergence helped to organize a tight inner core, and the central low pressure was maintained and enhanced by the aforementioned UL divergence.

Ok Thank you again . I know you are probably busy with this system.

[Frank P]

11 states are in the cone?...

don't see that very often

[TideJoe]

quick what way does this appear to be moving, anywhere

http://metofis.rsmas.miami.edu/~dortt/s ... 1_loop.gif

note i'm not sure how much detail one can get from this map, but i think you get the picture

Looks nearly stationary to me.

[Wthrman13]

Ooo Ok I see. Thank you. So this is what happened when Fay came in the first time?

It might have been part of it, but I don't think it was the whole explanation. A lot probably had to due with enhanced latent heat (moisture) flux from the Everglades, and the very favorable upper-level divergence over the storm. If I had to hazard a guess, I would say the frictional convergence helped to organize a tight inner core, and the central low pressure was maintained and enhanced by the aforementioned UL divergence.

Ok Thank you again . I know you are probably busy with this system.

Not really busy with it, no. I'm a researcher, not an operational forecaster, so I'm just keeping up with it out of interest (and possibly as a case to study in detail in the future) .

[tolakram]

Ok I'm confused. Looking at station locations west of the 8pm position I find the lowest pressure.

http://www.wunderground.com/wundermap/? ... 30&zoom=13



http://www.wunderground.com/wundermap/? ... 30&zoom=13


I also notice that weather underground is just plain not showing the 5pm position. Who decides when to ignore a position?

http://www.wunderground.com/wundermap/? ... re=0&tor=0

[cpdaman]

quick what way does this appear to be moving, anywhere

http://metofis.rsmas.miami.edu/~dortt/s ... 1_loop.gif

note i'm not sure how much detail one can get from this map, but i think you get the picture

Looks nearly stationary to me.

you win! i don't see this making it to the NHC's position at 2pm friday (on the edge of gulf) 18 hours away x appox 125 miles from current position = sustained movement of 7mph= not happening IMO

[KG4HPN]

I noticed that too, tolakram, but keep in mind that you're looking at a really unpopulated area of FL over there. Based on radar, I'd put the center somewhere just to the west of Ormond Beach, but there aren't really any weather stations in the area to look at pressure to verify.

I also noticed that the 8pm plot they put on their map is now pretty obviously west of what looks to me to be the current center. I can't help but wonder if their radar overlay is not in the right position, or if the plot point isn't right. The center of this thing can NOT have moved that much since 8pm (I noticed the discrepancy about 8:20).

Ok I'm confused. Looking at station locations west of the 8pm position I find the lowest pressure.

http://www.wunderground.com/wundermap/? ... 30&zoom=13



http://www.wunderground.com/wundermap/? ... 30&zoom=13


I also notice that weather underground is just plain not showing the 5pm position. Who decides when to ignore a position?

http://www.wunderground.com/wundermap/? ... re=0&tor=0

[paintplaye]

Ooo Ok I see. Thank you. So this is what happened when Fay came in the first time?

It might have been part of it, but I don't think it was the whole explanation. A lot probably had to due with enhanced latent heat (moisture) flux from the Everglades, and the very favorable upper-level divergence over the storm. If I had to hazard a guess, I would say the frictional convergence helped to organize a tight inner core, and the central low pressure was maintained and enhanced by the aforementioned UL divergence.

Ok Thank you again . I know you are probably busy with this system.

Not really busy with it, no. I'm a researcher, not an operational forecaster, so I'm just keeping up with it out of interest (and possibly as a case to study in detail in the future) .[/quote]

Ok well thank you again and good luck with your research

[HurricaneBelle]

Not really busy with it, no. I'm a researcher, not an operational forecaster, so I'm just keeping up with it out of interest (and possibly as a case to study in detail in the future) .

What will happen as a result of this storm is that every outlandish model run in the future that takes a TC in a strange direction or stalls it will be given additional credence as someone is sure to remark "but it happened with Fay" or "remember Fay".

[caribepr]

Ok, Uncle!!!! I'm taking on the burden of Fay, not exactly sure how this works but it's something about asking you all to pay attention to us in the islands year after year, and now I'm in Orlando, where what has become Fey Fay followed me; where I've just asked my daughter if that truly is mold on my toes. I give!!! I'll have all mercy for you all forever more (thought I did already but apparently not).
Excuse me, I have to go back to the altar of appeasement. Lucky for me, the sacrificial wine is waiting. But to keep it on topic, I believe the new questioned heading of WSW...Fay is going to center right on this house and then be on her way. It's all clear to me now.

[HurricaneBelle]

BEGIN
NHC
invest_al922008.invest
FSTDA
R
U
040
010
0000
200808101044
NONE
NOTIFY=ATRP
END
INVEST, AL, L, , , , , 92, 2008, DB, O, 2008081006, 9999999999, , , , , , METWATCH, , AL922008
AL, 92, 2008081006, , BEST, 0, 108N, 413W, 25, 0, DB, 0, , 0, 0, 0, 0,

And it all started so innocently, 11 days ago.

Kind of like Mrs. O'Leary and her cow.

[caneman]

I know RonJon mentioned this earlier but I'm a little bit unclear as to why Tampa/St.Pete isn't under TS Watch/Warning. In looking at radar and IR either the system is sinking/moving South or is expanding South. Winds have picked up here. Thoughts?