8/27/04 FCST: Frances (Atlantic)

[Austin Ivey]

Latest recon fix has found that the central pressure has increased to 944mb and FL winds have decreased.

Core convection around the eye is not very symmetric. Definitely a strong cat 4 signature but I don't think its well enough defined yet to attain cat 5. Frances seems to have been in a cyclic flux of eye replacements since early this morning and most of the day yesterday.

Everytime I hear about a storm with the potential to become cat 5, I compare the symmetry and convection intensity to that of Hurricane Mitch (the best looking atlantic basin hurricane i have ever seen).

Using Mitch as a comparison, Frances doesn't look like a cat 5.

However, as the NHC admits, we baiscally have no skill in predicting intensity changes in major hurricanes.

 

[David Wolfson]

Yeah, Glen. The track through the mid-Atlantic states and out just south of New England looks like Diane (1955) on steroids. I was five years old living south of Boston and remember the floods very well. I hope the 06Z GFS precip progs don't verify. They are very scary for the entire east coast and piedmont.

Unfortunately, I think the GFS is starting to get it right.

 

[Glen Romine]

Frances seems to have been in a cyclic flux of eye replacements since early this morning and most of the day yesterday.

And well before that. This is normal - strong hurricanes do this all the time. Whether the hurricane is in an "up" phase or a "down" phase at landfall can make a difference - but NHC has to be on the conservative side and so the forecast is based on the up cycle. The current noted weakening is consistent with the fact that Frances currently has an open eyewall, which you can see in current SSMI imagery.

Glen

 

[Cstok]

Interesting to see how all of the models play out in one graphic.

http://www.boatus.com/hurricanes/hurricane...e_spaghetti.asp

 

[Jeff Snyder]

Well... The trends noted in satellite imagery seem to be coinciding pretty well with the latest NHC intermediate public advisory (2pm AST/EDT). The eye continues to look less and less impressive with time since last night, and appeared earlier like it was collapsing in. The eye on a 1745z infrared image looks very very small, and recon mentions that the eye is open to the S-SW. In addition, cloud tops are warm/warming in the northern semi-circle. Nonetheless, there have been a couple of persistent flareups / convection cloud-top cooling immediately north of the eyewall, which is likely what is keeping it at the 2pm intensity of 145mph. I can't imagine that the winds won't be lowered on the 5pm advisory unless we see an upswing on the organization. Outflow continues to look quite impressive still, however. 949mb hurricane usually doesn't support 145mph winds. 939mb -- yes, but it's not typical for a 949mb 'cane. In the past few years, 949mb has been mainly associated with sfc winds of 110-115kts ... Of course size does make a difference, as do many other factors, but largely this has been the case...

That said, all conditions appear favorable. Assuming we see an upswing in organization later today (re-establishment of a closed/symmetric eye, etc), this reorganization could be bad news for FL folks. Typically, storms can only maintain strong Cat 4 or Cat 5 strength for 18-30 hours (Mitch had 155kt winds and maintained cat 5 strength for 42-48 hours :shock: ), and thus a strengthening today would have likely meant a slight weakening tomorrow (climatologically- and statistically-speaking of course)...

 

[Mike Peregrine]

Have been watching the forecast plot inch its way closer to the Gulf Coast ... possibly in response to the relative harmonization of several of the models now.

http://hurricane.terrapin.com/ATL-06A/ftrack.html

Current position is: 23.4°N 73.9°W Movement is NW@11kt

Est. min. pressure at 949 MB per 11:00 a.m. warning statement.

Max sustained 125 kt, max gust 155 kt.

Just eyeballing it (and with like zero experience in this sort of thing) - still looks like landfall could most likely be anywhere from Boca to Cocoa Beach, with the highest interest (in my mind) centered on the area around W. Palm Beach.

Miami is also still very much in the running with the latest strike probabilities:

http://hurricane.terrapin.com/text/1094150...1US.TXT.html.en

Earl Barker has now included some specialized modeling products just for Frances ... definitely worth having a look:

http://www.wxcaster.com/frances.htm

Includes data runs for MM5, NOGAPS, and GFS all in one convenient spot.

Take a look at the COD regional satellite page ... that poor little island in the Bahamas is about to take a direct hit ... looks like it will be completely enveloped by the eye:

http://weather.cod.edu/analysis/satrad.regional.html

 

[Austin Ivey]

Weakening is commencing at the moment with Frances. Correct me if I'm wrong, but didn't Andrew go through the same sort of intensity cycle. IE, decreasing intensity about a day before landfall then rapidly intensified once it hit the warm gulf stream waters? I bet this is the reason why the 2pm advisory did not show a decrease in wind speeds. They don't want the public to let their guard down.

I've never heard or read about a 949mb storm with 145mph sustained winds.

 

[Mike Peregrine]

I was about to note the same thing, Austin ... even with apparent weakening, it's still over relatively deep water. It's about to hit the Gulf Stream current and the warmer shallows around the islands. Anyone have any links to buoy readings out there? - Would be interested to note the differences in water temps between its current position and that of the Gulf Stream waters -

They are probably equally cautious following Charley's rapid strengthening cycle just prior to landfall. Any references to weakening in statements - especially if highlighted by the media - would likely encourage people to lighten up on the evacuation and preparation efforts. They need to continue taking this seriously down there, even with possible storm cycling.

 

[Jeff Snyder]

Well, latest recon actually shows 948mb, a 1mb decrease in the past hour or two. The eye seems to have almost completely collapsed, as it is barely evident in the latest vis and infrared imagery.

NWSFO Melbourne FL has a pretty good discussion (their pm AFD), which has some interesting info in it --> http://kamala.cod.edu/offs/KMLB/0409021844.fxus62.html LOL Then again, they did have 3 people write it.

 

[David Wolfson]

Mike, this is a nice ocean temp chart: https://128.160.23.54/products/K10/caribbeank10.gif

Looks like temps rise by about one degree C.

 

[Tim Vasquez]

In addition to David's good link there is also this:
http://www.osdpd.noaa.gov/PSB/EPS/SST/data...S_km14f7n00.gif

Certainly seems to suggest the storm is getting into a more favorable environment, as Mike P suggested.

 

[Bob Schafer]

I'm just eyeballing too, but, man, it sure is starting to look to me that Frances has turned north, and will completely miss Florida.

I hope so.

Bob

 

[Zach Bailey]

I'm just eyeballing too, but, man, it sure is starting to look to me that Frances has turned north, and will completely miss Florida.

I hope so.

Bob

ATTEMPTING TO EXTRAPOLATE SHORT TERM (1-3HR) TROCHOIDAL WOBBLES
INTO A LONGER TERM MOTION IS PRONE TO BE ERRONEOUS...ESPECIALLY
GIVEN THE CURRENT FORWARD SPEED

from http://kamala.cod.edu/offs/KMLB/0409021844.fxus62.html

I thought the same thing when I saw the satellite pictures too, however weird things happen to a hurricane's motion when the eyewall collapses. Basically the physics of angular momentum comes into play and it causes the hurricane to wobble off course until the eyewall comes back to some sort of dynamic equilibrium and the track straightens out. Then of course the process repeats all over again.

I would certainly love to see it turn north and save florida, as well, but don't be misled when eyewall replacement cycles are taking place.

 

[RodgerHeckman]

It does look as though the NW turn, that a few of the models had predicted could be in progress, although it may be a part of an eye replacement cycle. If that turn holds to the NW a bit longer, then its ulikely the eye of Frances will impact my area of S. Florida, so I may hit the road later and head up to some friends of mine on the Central FL east coast.

I did order some new portable weather instruments last week expecting to have them in time for a possible chase, but unfortunatly I just received this tracking message from UPS

"Sep 2, 2004
2:56 P.M.
HIALEAH, FL, US
THE PACKAGE IS DELAYED DUE TO EMERGENCY CONDITIONS BEYOND UPS' CONTROL"

Atleast I have my AV equipment tested and ready, while I try to figure out what the latest path Frances may take.

 

[Zach Bailey]

As for trochoidal wobbles - I've found a good image that illustrates just exactly what these are and how it can affect the path of the hurricane.

Image: (it's big, I'm not sure how the boards will handle it. You may need to click on it or go here: http://www.unc.edu/~znbailey/troch.GIF )

[Broken External Image]:http://www.unc.edu/~znbailey/troch.GIF

Basically what this image illustrates is hurricane carla moving fairly NW towards the TX gulf coast. Notice how for a while it will go almost north, then completely turn to the left for a little while. This is the result of the trochoidal wobble, which as far as I understand it comes from the fluid dynamics (wave numbers, etc.) present in the rotation of a hurricane.

For the paper from which I took the image, see:

]http://eliassen.atmos.colostate.edu/papers...oidal.pdf[/img]