Florence is born

By: Dr. Jeff Masters , 3:47 PM GMT on September 05, 2006

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Tropical Depression Six got enough heavy thunderstorm activity surrounding its center to be upgraded to Tropical Storm Florence at 11am EDT. Florence doesn't look much like a tropical storm on satellite imagery, with a very broad center and the main thunderstorm activity well removed from the center. Maximum winds of 30 knots (35 mph) were seen on this morning's 4:33am EDT QuikSCAT pass (Figure 1), which are just below tropical storm force. However, the winds in Figure 1 were taken from the low-resolution 25 km QuikSCAT product, and the higher-resolution 12.5 km QuikSCAT winds did show a few areas of tropical storm force winds. These stronger winds were given as justification for upgrading to a tropical storm. Given the disorganization of the storm and marginal tropical storm force winds on QuikSCAT, the system could have just as easily been held as a tropical depression for one more advisory. The 12.5 km QuikSCAT product is noisier and more prone to error than the standard 25 km product, and is not always used by NHC to make a judgement about upgrading to a tropical storm.

Florence has managed to consolidate the two circulation centers it was struggling with yesterday into one large circulation center. It will probably take another day before the winds tighten up around the center and Florence can begin any substantial intensification. Interfering with this process will be about 10-15 knots of shear and some dry air to the north. The shear should lessen by Thursday, potentially allowing Florence to become a hurricane.

The computer models all forecast that Florence will pass north of the Lesser Antilles Islands, although it is too far in the future to be highly confident of this forecast. A complicating factor is the development of a new disturbance about 800 miles to the east-southeast. This new disturbance, officially designated "Invest 91L" this morning by NHC, is close enough to alter both the strength and track of TD 6. Anytime two storms get within 13 degrees of arc of each other (900 miles), the two storms tend to rotate around a common center (the Fujiwhara effect). The computer models do make some allowances for this effect, but are not very good at handling it. For this reason, one should be suspicious of the track and intensity forecasts for Florence and 91L as long as they are so close. The intensities of both storms can also change as a result of the interaction, with both storms intensifying at a slower rate than they otherwise would, or one storm growing at the expense of the other. If the two storms approach within about 7 arc-degrees of each other (480 miles), this is considered the "zone of death" where one cyclone will surely destroy the other. The surviving storm will not be a "superstorm" that has the combined size and strength of the two storms, however.

The long-range GFS model forecast continues to show Florence becoming a powerful hurricane that threatens Bermuda, but recurves out to sea well east of the U.S. East Coast. Again, it is too early to be confident of this forecast. Keep in mind that early model forecasts are often very unreliable. That is because the center is not well established and often relocates, and that subtle difference can make major
track changes. Also, the global models such as the GFS, UKMET, and NOGAPS represent a weak storm as a very diffuse entity, and that causes problems for the global models and the "zoomed in" models like the GFDL that use a global model (the GFS) as their starting points. Be wary of the track forecasts until the system becomes more established. Tomorrow morning we should have a better idea of the models' reliabilty, since Florence should be better established.


Figure 1. QuikSCAT satellite winds from 4:33am EDT Tuesday September 5 2006. Wind speed and direction are coded according to the standard station model, and are color coded (in knots) according to the color scale at the upper right (10 knots = 11.5 mph). Black winds barbs occur where there is rain, and one cannot trust the wind speeds measured in those areas. Tropical storm force winds (35 knots) are colored red and need to have 3 long bars and one short bar attached to the end of the "barb"; there is one barb like this on the east side of TD 6, but it is pointing a different direction than the other barbs around it, and is surrounded by rain-contaminated (black) barbs. One should be suspicious of the accuracy of this lone tropical storm force wind barb.


Figure 2. Preliminary model tracks for Invest 91L, a well-organized tropical wave a few hundred miles west of the Cape Verde Islands.

Cape Verdes Islands tropical wave
A strong new tropical wave emerged from the coast of Africa Saturday and is a few hundred miles west-southwest of the Cape Verde Islands. The wave has a closed circulation, and visible satellite imagery from this morning shows an increase in thunderstorm activity on the west side. The wave is over warm water and is under a modest 10 knots of wind shear, and could be Tropical Depression Seven by Wednesday. Due to its more southerly starting position, this system is more likely to be a threat to land than Florence.

Carolinas
North Carolina is still suffering flooding problems from Ernesto. Where Ernesto came ashore at Cape Fear, North Carolina, the North Cape Fear River is at 16.6 feet, and flood stage is only 10 feet. This is the second highest flood on this river; only Hurricane Floyd of 1999 caused a higher flood. With a strong cold front expected to move through tonight and stall offshore, North Carolina will receive another 1-2" of rain that will make flooded areas slow to recover. Once this cold front does stall over the warm Gulf Stream waters, we need to watch the area off the Carolina coast for possible tropical storm development.

Ioke
Ioke continues its slide into oblivion, and is now a mere tropical storm. Ioke is caught in a large trough of low pressure that is weakening it and recurving it out to sea. Ioke is not a threat to any land.

Next update
I'll have an update Wednesday morning, unless there's something interesting to report on this afternoon.

Jeff Masters

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1990. thelmores
5:56 PM GMT on September 06, 2006
looks like we have 92L on the navy site...... for the "disturbance" off the SE coast...



Member Since: September 8, 2005 Posts: 0 Comments: 3805
1989. miracleaa1990
2:39 PM GMT on September 06, 2006
ok Ray - I LOVE your thinking - cuz I want the Cape to get hit, too. I'm an adjuster and the Cape could mean an early retirement. IF it's gonna hit the States, that is. After KAtrina, I quit wishing hurricanes on anyone. I still think of the people in Mississippi daily. They are real troopers. Anyway, more moderate hurricanes, like the 3 that went over my house - Frances, Jean, Wilma - were actually easy to deal with - and, incidentally, the models were screwy on them, too
Member Since: August 1, 2006 Posts: 0 Comments: 284
1988. thelmores
2:38 PM GMT on September 06, 2006
"Florence is a large circulation thus WILL survive the shear."

hmmm... i was under the impression that "sometimes" the smaller, more shallow circulations are better at weathering shear. to be honest, not sure if there is such a correlation between the two. i guess i could make arguments for each.....
Member Since: September 8, 2005 Posts: 0 Comments: 3805
1987. seminolesfan
2:36 PM GMT on September 06, 2006
Posted By: RAYFROMBOSTON at 2:27 PM GMT on September 06, 2006.
No, Seminolesfan, what I am saying is there are some things entered in, but the ultimate positions of the aforementioned factors are output, not input.


duh...its a forcast model(btw-you should replace 'ulitmate' with 'assumed future'




I'm going over to tha new blog.
Member Since: June 14, 2006 Posts: 0 Comments: 2108
1986. K8eCane
2:34 PM GMT on September 06, 2006
i have a word for everyone to ponder


bush
Member Since: April 26, 2006 Posts: 5 Comments: 3098
1985. seminolesfan
2:32 PM GMT on September 06, 2006
Posted By: seminolesfan at 2:11 PM GMT on September 06, 2006.
SEFL-OK, I'm gonna work backwards here to the orginal point.

I'm sure you have heard the term 'Garbage In...Garbage Out' before.

Put simply; if the information input into an algorithm(ie-model) contains incorrect information or incorrect assumptions, the output of said algorithm must also be put into question.

Posted By: SEFL at 2:23 PM GMT on September 06, 2006.
but 'something' has to get entered into the model for it to run, right?

Here we disagree. I don't think that just "something" gets entered into the models. What gets enter is the best information that the weather experts have given the admitted uncertainty of weather forecasting.

You are now the one trying to deal in early morning semantics. :)(I already said that my first comment was semantics; I then asked if it was too early for such word games.)

I now consider this 'conversation' completed; my point has been made. I would now like to turn my attention to 'nowcasting'. Word games are too easy. :)
Member Since: June 14, 2006 Posts: 0 Comments: 2108
1984. K8eCane
2:31 PM GMT on September 06, 2006
the models do leave me a little hopeful since they are all in agreement
Member Since: April 26, 2006 Posts: 5 Comments: 3098
1983. Rick54
2:30 PM GMT on September 06, 2006
That's a great question. I imagine the NHC would like that answer as well.

The guys at the NHC have a job to do...
Every few hours they have to come up with a prediction that goes out as far as 5 days and even though the models are in agreement experience is telling them that it is likely that the upper level conditions are not going to work out as planned. I don't think they really know yet if it is going to turn sooner because the trof is deeper or if it is going to turn more Westerly because the trof pulls out sooner.

What I see in the models at this point is a trof existing and not much more.
1982. K8eCane
2:29 PM GMT on September 06, 2006
wow
has the georgia blob persisted?
Member Since: April 26, 2006 Posts: 5 Comments: 3098
1981. SavannahStorm
2:28 PM GMT on September 06, 2006
Wow, um, has anyone noticed the Georgia Blob this morning? I thought the clouds look wierd this morning, low and racing to the SW...
Member Since: September 22, 2005 Posts: 18 Comments: 2323
1980. RAYFROMBOSTON
2:27 PM GMT on September 06, 2006
No, Seminolesfan, what I am saying is there are some things entered in, but the ultimate positions of the aforementioned factors are output, not input.
1979. SEFL
2:26 PM GMT on September 06, 2006
Posted By: Randrewl at 10:21 AM EDT on September 06, 2006.
SEFL...As long as there are variances from the forecast motion there will be faulted model runs. These things are going to keep shifting around until something stabilizes. Perhaps it never will.

I certainly agree with you. I started trying to understand the different points of view...I appreciate those. But, and I know better having read this blog for years, some people want to disagree just to disagree and some want to disagree to be disagreeable, and some just think they know weather forecasting better than others. But I still ask the questions so I can get an idea of whose ideas are worth reviewing for further consideration.
1978. vortextrance
2:26 PM GMT on September 06, 2006
guys new blog up
Member Since: October 5, 2005 Posts: 0 Comments: 700
1977. seminolesfan
2:24 PM GMT on September 06, 2006
ray-seriously,

are you trying to tell me each model 'looks out the window' for its initial conditions?

Let's be real here...I'm starting to feel like you and SEFL are messin with me today.
Member Since: June 14, 2006 Posts: 0 Comments: 2108
1975. SEFL
2:23 PM GMT on September 06, 2006
but 'something' has to get entered into the model for it to run, right?

Here we disagree. I don't think that just "something" gets entered into the models. What gets enter is the best information that the weather experts have given the admitted uncertainty of weather forecasting.

You are now the one trying to deal in early morning semantics. :)
1974. RAYFROMBOSTON
2:21 PM GMT on September 06, 2006
Seminolefan, the models figure those things out, they are not entered in.
1972. RAYFROMBOSTON
2:20 PM GMT on September 06, 2006
LOL, I agree about Kennedy, but actualy ur wrong, I'd like too see it! I would luv to get a cane cause it's been a long time coming.
1971. seminolesfan
2:19 PM GMT on September 06, 2006
Okay-In addition to the "hard to pin down" coc and other near area variables(91L,shear,movement direction, etc.)there are 3 synoptic variables in question.
1.The Trof
2.The Bermuda High/Ridge
3.How fast the Canadian High will build in behind the trof.

All these factors are not set in stone, but 'something' has to get entered into the model for it to run, right?
Member Since: June 14, 2006 Posts: 0 Comments: 2108
1970. SavannahStorm
2:19 PM GMT on September 06, 2006
shnikeys, Flo's one big girl. If it weren't for the sheer and dry air she'd be bigger than Texas! That loop makes me still think she's movinh due W if not WSW.
Member Since: September 22, 2005 Posts: 18 Comments: 2323
1969. SEFL
2:18 PM GMT on September 06, 2006
Posted By: Rick54 at 10:15 AM EDT on September 06, 2006.
Posted By: SavannahStorm at 2:11 PM GMT on September 06, 2006.
I wouldn't say NHC "has no clue," but the last few forecast discussions have shown they have low confidence in their forecast. For example:

Unfortunately...the globals continue to show discrepancies in the
evolution of an upstream short-wave trough moving through the
eastern United States this weekend.
aforementioned northward turn.

Instead of focusing on the track shouldn't this be what everyone is focusing on? Does anyone have any thoughts on the matter? Does the weather pattern over the US seem to be setting up as the models are predicting? Slower ? Faster?

I asked this question an hour ago and got only one response.
1968. miracleaa1990
2:17 PM GMT on September 06, 2006
hey Ray - mowst on here are only saying that FLO is moving due west and therefore, the models cannot be trusted until they get a few runs with a real fix - the rest of the fish storm or landfall stuff is just grabassing - there is little doubt the models will change again, as the storm is definitel moving west - I know you want it to go out to sea, and this not be the one that gets the cape- I've had 3 come directly over my house the past 2 years- just make sure ted kennedy is tied to a tree at sea level if it comes your way
Member Since: August 1, 2006 Posts: 0 Comments: 284
1967. SEFL
2:17 PM GMT on September 06, 2006
Posted By: Randrewl at 10:13 AM EDT on September 06, 2006.
Still moving more West than North. Check the chart and notice the XTRP has shifted down on the 12Z from where it was.

so wouldn't that support that the initial motion in the models/forecast is indeed more toward the west, since it is the initial motion that is extrapolated?
1966. RAYFROMBOSTON
2:16 PM GMT on September 06, 2006
I hear u Savanahstorm, but how can people say "garbage in, garbage out" when the models have been consistently spitting out the same "garbage" for over 24 hrs. I have my doubts too, but they are mitigated with each new run showing the same consecus.
1965. Rick54
2:15 PM GMT on September 06, 2006
Posted By: SavannahStorm at 2:11 PM GMT on September 06, 2006.
I wouldn't say NHC "has no clue," but the last few forecast discussions have shown they have low confidence in their forecast. For example:

Unfortunately...the globals continue to show discrepancies in the
evolution of an upstream short-wave trough moving through the
eastern United States this weekend.
aforementioned northward turn.

Instead of focusing on the track shouldn't this be what everyone is focusing on? Does anyone have any thoughts on the matter? Does the weather pattern over the US seem to be setting up as the models are predicting? Slower ? Faster?
1964. SEFL
2:14 PM GMT on September 06, 2006
"Do we agree on this?"

Yes.
1962. vortextrance
2:13 PM GMT on September 06, 2006
They all make me cross eyed after a while SEFL.
Member Since: October 5, 2005 Posts: 0 Comments: 700
1961. RAYFROMBOSTON
2:13 PM GMT on September 06, 2006
Vortexenrance, I think the people of this forum would be better served following ur line of thought.
1960. SavannahStorm
2:11 PM GMT on September 06, 2006
I wouldn't say NHC "has no clue," but the last few forecast discussions have shown they have low confidence in their forecast. For example:

Unfortunately...the globals continue to show discrepancies in the
evolution of an upstream short-wave trough moving through the
eastern United States this weekend. This results in differences
among the models in the degree...timing...and location of the
aforementioned northward turn.
Member Since: September 22, 2005 Posts: 18 Comments: 2323
1959. seminolesfan
2:11 PM GMT on September 06, 2006
SEFL-OK, I'm gonna work backwards here to the orginal point.

I'm sure you have heard the term 'Garbage In...Garbage Out' before.

Put simply; if the information input into an algorithm(ie-model) contains incorrect information or incorrect assumptions, the output of said algorithm must also be put into question.

Do we agree on this?
Member Since: June 14, 2006 Posts: 0 Comments: 2108
1958. vortextrance
2:11 PM GMT on September 06, 2006
I don't either Boston. I always read their discussions to help form my opinions. I don't dispute a turn to the north. I am not calling for a US landfall. I just wonder when the turn will happen and how strong it will be. These are not original thoughts. They came straight from the NHC discussion. Thats why I am not willing to say fish storm or US landfall, neither is the NHC.
Member Since: October 5, 2005 Posts: 0 Comments: 700
1957. RAYFROMBOSTON
2:10 PM GMT on September 06, 2006
Gulfscotsman, the point u are forgetting is that inlike Ernesto, Chris, etc, Florence is a large circulation thus WILL survive the shear.
1956. miracleaa1990
2:09 PM GMT on September 06, 2006
and there is no question this sucker is headed due west- even if you can't see the exact "center" - look at the southern edge of the exposed "coc"- it's been cruising due west at 15 degrees forever
Member Since: August 1, 2006 Posts: 0 Comments: 284
1955. RAYFROMBOSTON
2:07 PM GMT on September 06, 2006
Vortexentrance, u have a point there, but I dont understand those that dont think the NHC has a clue!
1954. SEFL
2:07 PM GMT on September 06, 2006
Posted By: vortextrance at 10:05 AM EDT on September 06, 2006.
I think the NHC isn't sure where the center is. They mentioned earlier its been jumping around, maybe reforming to the north. Its very much the same scenario that hapened with Ernesto. They either couldn't find the center or the center kept moving around. So I don't think its a matter of them not realizing so much as being on sure of the true center. Flo is a disorganized mess, not easy to forecast or nowcast.

Ah, thank you....so any attempt to find a center will probably make you cross-eyed.
1952. miracleaa1990
2:06 PM GMT on September 06, 2006
17.9/50.8 - those are the coordinates - now...someone put these into the models so we can get a proper forecast
Member Since: August 1, 2006 Posts: 0 Comments: 284
1951. vortextrance
2:05 PM GMT on September 06, 2006
I think the NHC isn't sure where the center is. They mentioned earlier its been jumping around, maybe reforming to the north. Its very much the same scenario that hapened with Ernesto. They either couldn't find the center or the center kept moving around. So I don't think its a matter of them not realizing so much as being on sure of the true center. Flo is a disorganized mess, not easy to forecast or nowcast.
Member Since: October 5, 2005 Posts: 0 Comments: 700
1950. RAYFROMBOSTON
2:02 PM GMT on September 06, 2006
Glad u see that to SEFL! : )
1949. RAYFROMBOSTON
2:01 PM GMT on September 06, 2006
Gulfscotsman,LOL, u cant argue with wishcasters and apparently the NHC doesnt know how to determine latitude and longitude! : )
1948. NCsnidget
2:01 PM GMT on September 06, 2006
You do have to remember a model is only as good as the data we have and the data set the model was built on. Each year of data means they will get better, but no model is ever perfect.

Not trusting they are 100% accurate (no model is) doesn't mean you should expect the storm to do something totally bizarre at any moment (although some of the wishcasts here are truely innovative). There is always going to be a small probability for bizarre, but usually you do get some warning of that in the models.

I remember Dennis spinning off the coast the year Floyd hit. Cone of probability looked like a bullseye, for days. We know it will be somewhere, maybe.

Not trusting it enough to decide if you need to put up the plywood 5-10 days out is not the same as it has absolutely zero predictive value which is what some people seem to hear when you say you can't trust the models.

I'm almost completely sure it will be west of where it is and north of where it is 5 days from now. I'll keep an eye out to see if something shifts it more toward hitting the coast, but the odds aren't looking good for that (although with hurricanes the goods are always just a little odd)
1947. SEFL
2:01 PM GMT on September 06, 2006
Posted By: seminolesfan at 9:58 AM EDT on September 06, 2006.
SEFL-WTF?

Are you tryingto misunderstand me?

Did I misquote you? I'm actually trying to understand you.
1946. Cavin Rawlins
2:01 PM GMT on September 06, 2006
Shouldnt we be happy that Florence is heading out out sea?
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1945. Zaphod
2:00 PM GMT on September 06, 2006
Au contraire, whenever I question the models I ALWAYS endeavor to explain my concern.

In this case, as stated before, I question the obvious error in position initialization, the apparent initial motion vector error, the implausible handling of 91L, and the large size and uncertain structure of the storm in general.

Once the initialization is clean, the models should do well, and I suspect they accurately read the synoptic scale trends. The remaining question once the initialization is good (which won't be until tomorrow or maybe even Friday, I suspect) is how sensitive the track is to the initial position. If it is insensitive, then the recurve is very likely. If it is on the cusp, then we cannot know until the initial location gets sorted out.

Or I could just be wrong, and the odd 91L vectors pan out (though they are very divergent now), and the models already take into account the inter-storm coupling.
Zap
Member Since: October 5, 2005 Posts: 15 Comments: 3239
1944. SEFL
1:59 PM GMT on September 06, 2006
Posted By: nash28 at 9:56 AM EDT on September 06, 2006.
No Ray, I don't.

Thats pretty arrogant.
1943. FLKEYSRADIO
1:59 PM GMT on September 06, 2006
no, technically they are mammals.
1942. thelmores
1:59 PM GMT on September 06, 2006



humor me..... have been watching this wave that is ssw of the cape verdes.... not sure exactly why, other than intuition.......

if you look closely, seems you can ALMOST make out the LLC....
Member Since: September 8, 2005 Posts: 0 Comments: 3805
1941. RAYFROMBOSTON
1:58 PM GMT on September 06, 2006
Well Nash, I think ur in the minority on that one, but u have a right to ur opinion and I respectfuly disagree.

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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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