90L NHC Model run up......

[Derecho]

TROPICAL DEPRESSION INVEST (AL902004) ON 20040729 1200 UTC

...00 HRS... ...12 HRS... ...24 HRS... ...36 HRS...
040729 1200 040730 0000 040730 1200 040731 0000

LAT LON LAT LON LAT LON LAT LON
BAMD 25.5N 83.0W 24.8N 84.4W 24.3N 85.9W 24.2N 87.6W
BAMM 25.5N 83.0W 25.3N 84.3W 25.3N 85.5W 25.4N 86.9W
A98E 25.5N 83.0W 25.5N 84.3W 25.3N 85.7W 24.6N 87.1W
LBAR 25.5N 83.0W 25.4N 84.4W 25.8N 86.0W 26.4N 87.8W
SHIP 20KTS 22KTS 27KTS 33KTS
DSHP 20KTS 22KTS 27KTS 33KTS

...48 HRS... ...72 HRS... ...96 HRS... ..120 HRS...
040731 1200 040801 1200 040802 1200 040803 1200

LAT LON LAT LON LAT LON LAT LON
BAMD 24.4N 89.3W 25.1N 93.0W 25.4N 96.3W 25.0N 99.8W
BAMM 25.8N 88.4W 26.8N 91.3W 27.0N 93.8W 26.3N 96.8W
A98E 24.2N 88.5W 23.5N 90.9W 23.1N 93.2W 22.6N 96.1W
LBAR 27.5N 89.4W 30.0N 90.8W 32.4N 89.9W 33.7N 88.2W
SHIP 41KTS 52KTS 60KTS 68KTS
DSHP 41KTS 52KTS 60KTS 68KTS

...INITIAL CONDITIONS...
LATCUR = 25.5N LONCUR = 83.0W DIRCUR = 270DEG SPDCUR = 7KT
LATM12 = 25.5N LONM12 = 81.6W DIRM12 = 270DEG SPDM12 = 7KT
LATM24 = 25.5N LONM24 = 80.0W
WNDCUR = 20KT RMAXWD = 20NM WNDM12 = 20KT
CENPRS = 1011MB OUTPRS = 1014MB OUTRAD = 150NM SDEPTH = D
RD34NE = 0NM RD34SE = 0NM RD34SW = 0NM RD34NW = 0NM




Once I get my tropical site up (next year) I hope to have really rapidly updated plot maps.

I doubt these plots will be too popular, and I have a feeling I'm going to be giving my "why the LBAR sucks" speech in a few minutes.

[HURAKAN]

Looks like Alex and Bonnie are touching our doors.

[Ola]

I normally only look at the BAMD and BAMM. Isnt the LBAR a statistical straight forward model? Im confused now because if it was then it would not turn a storm back around. Put some light on my ignorance Derecho.

[Derecho]

No, there are no real fully statistical models run anymore....Even A90E is only half statistical.

LBAR isn't a statistical model, it's just ancient, and very simple. And gets really, really, really bad once the latitude of a storm increases (above 20N).

[Derek Ortt]

I wouldnt pay attention to any of the BAM models as the environment is NOT barotropic

[Ola]

I wouldnt pay attention to any of the BAM models as the environment is NOT barotropic

So BAM models are better for barotropic conditions meanin a storm in the deep tropics? And other models are better above 20 North? Or do you mean a pure tropical development from the surface up and not from the upper levels to down levels?

[Wthrman13]

Ola,

The BAM models aren't barotropic models (the LBAR is). They are trajectory models based on the vertically averaged winds from the GFS model over a certain layer. The storm is assumed to move with these vertically averaged winds.

See

http://www.nhc.noaa.gov/aboutmodels.shtml

[Ola]

I wouldnt pay attention to any of the BAM models as the environment is NOT barotropic

From this statement I understand that if the environment was barotropic then he would pay attention to the BAM models.

But.....

The BAM models aren't barotropic models (the LBAR is).

Now I am really confused. You are both contradicting or is it me?

[Derek Ortt]

I was always under the assumption that the BAM models were barotropic advection models

[Derek Ortt]

In any event, only use a barotropic model when there is a barotropic atmosphere (meaning low shear i.e. geostrophic wind remains the same with height, or at least equivalent barotropic)

[Wthrman13]

Derek,

technically, the BAM (stands for Beta and Advection Model) models use a vertically averaged horizontal wind from the GFS model to calculate the tropical cyclone trajectory. What layer it does the vertical averaging over determines whether it is the BAMS, BAMM, or BAMD. Since it uses a vertically averaged horizontal wind, in that sense I guess it could be called a barotropic or equivalent barotropic model. I'll try to dig up the original technical memo that describes the BAM models and see what it says.

When I say barotropic model, I mean a model that actually solves the dynamical equations with the assumptions of a barotropic atmosphere in place (i.e. no density or temperature gradients along pressure surfaces). The LBAR does this, but uses the GFS model for it's boundary conditions. That's why it is so lousy, because it's so absurdly simplified (actually represents the atmosphere as a single horizontal layer).

[southerngale]

Is there a model map yet?

[lilbump3000]

I thought they would have posted some by now, but i found some with the latest 18Z runs.

Invest 90L




Invest 99L

[southerngale]

Thanks lilbump3000 - still all over the place with the GOM system but I guess that's to be expected.

[Stormchaser16]

The track of 99L really depends on a few things- the Western Atlantic ridge and the oncoming frontal boundary/trough. The trough is taking its sweet old time making it across the country, however when this does meet with 99L it will likely pull it on a more WNW-NW track, however of an interesting note is the Bermuda High and its effects on the frontal system. If the frontal system stalls as the Bermuda High builds in, im not exactly sure what would happen to the system.... would need someone elses help with this, and how this would affect 99L, any comments much appreciated.

[Derek Ortt]

Thanks for the clarification about it being the beta and not barotropic advection.

The averaged wind does tend to over simplify the atmosphere though, which may be why there are the problems when it encounters troughs, etc and really only performs well in barotropic conditions.

As for LBAR, I only recall it doing well for Georges near the Islands, and that was when the environment was nearly purely barotropic (absolutely no shear whatsoever and no baroclinic features within about a thousand miles of the system)

[Ola]

Thanks to both of you really.

Derek and Wthr