Hurricane Isaac - Cat. 1

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Thunder44
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Re: 2:00 pm Discussion...

#161 Postby Thunder44 » Fri Sep 22, 2006 1:15 pm

Weathermaster wrote:TROPICAL WAVE IS ALONG 39W S OF 19N WITH A 1010 MB LOW ALONG THE
WAVE NEAR 12N MOVING W 15 KT. BROAD MID LEVEL CYCLONIC ROTATION
COVERING A LARGE AREA WITH CLUSTERS OF SCATTERED MODERATE TO
ISOLATED STRONG CONVECTION FROM 10N-19N BETWEEN 32W-41W. THIS
SYSTEM IS SHOWING SIGNS OF ORGANIZATION
...AND SOME GRADUAL
DEVELOPMENT IS POSSIBLE OVER THE NEXT FEW DAYS AS IT MOVES TOWARD
THE WEST-NORTHWEST OR NORTHWEST AT 10 TO 15 MPH.


This is probably from this morning's discussion which they really insert a quote from the 5:30am TWO.
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#162 Postby HUC » Fri Sep 22, 2006 1:16 pm

You can read tht the wave at 39W has not become any better organised,and no"is showing size of organisation"
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#163 Postby SouthFloridawx » Fri Sep 22, 2006 1:16 pm

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#164 Postby HUC » Fri Sep 22, 2006 1:18 pm

Thannk's to the real text of the 2pm TWD
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#165 Postby SouthFloridawx » Fri Sep 22, 2006 1:25 pm

Perhaps that was this mornings text from the 805?
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#166 Postby MiamiensisWx » Fri Sep 22, 2006 1:25 pm

SouthFloridawx wrote:Perhaps that was this mornings text from the 805?


I believe so as well, as Thunder44 mentioned beforehand.
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#167 Postby SouthFloridawx » Fri Sep 22, 2006 1:29 pm

96L appears to becoming very very slowly organized.
http://hadar.cira.colostate.edu/ramsdis ... _ls_0.html
:uarrow: :uarrow: Atlantic Loop

http://hadar.cira.colostate.edu/ramsdis ... at1_0.html
Floater Loop :uarrow: :uarrow:

It is still being sheared by that ULT to the North of it.
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#168 Postby MiamiensisWx » Fri Sep 22, 2006 2:16 pm

Well, currently Helene is gradually gathering extratropical characteristics and may complete extratropical transition within the next 36 to 48 hours - or even slightly sooner - as it merges with the middle to upper-level trough currently associated with an ULL (which is located to the north-northwest of Helene) located in the west-central to central North Atlantic, as apparent on visible and water vapor imagery. As Helene merges with ULT in the north-central North Atlantic associated with the aforementioned ULL near 55N and 54.9W, the southern portion of the ULT may cut off, weaken, and develop into a newer weak ULL in the vicinity of 24.5N and 56.5W while the northern portion of the ULT pulls out while Helene merges with it within the next 56 hours while becoming more entrenched with the westerlies as an extratropical low.

Image

As evidenced, you can already see the beginning stages of a weak ULL forming as the southern portion of the ULT cuts off and retrogrades slightly westward as the more northerly portion of the ULT associated with the aforementioned other ULL over the far northern North Atlantic pulls out with Helene. This, along with allowing the southern portion of the ULT to cut off, weaken, retrograde slightly westward, and form into a weak ULL (as it is currently doing and how the beginning stages of this whole process is evident on current visible loops as the northern portion of the ULT pulls out), may help to significantly decrease the mid-level shear over and just ahead of 96L by 36 to 48 hours and beyond. Based on loops, you can see the beginning stages of this due to all the aforementioned details in earnest.

As the northern portion of the ULT pulls out within the next 36 to 48 hours and as a weak and shallower ULL forms from the weakening southern portion of the trough near 24.5N and 56.5W and retrogrades slightly westward, mid-level ridging off the Mid-Atlantic region may build in eastward by 36 to 48 hours and lasting until roughly 64 hours in advance of a developing mid-level trough in the eastern Great Plains, additionally helping to reduce shear in the region ahead of 96L from roughly 54W to 74.8W. You can see the beginning process of this on this surface map; additionally helping in this process, a surface front just behind the ULT over the north-central North Atlantic pulling out with Helene may weaken by 36 to 48 hours, allowing this ridging to build eastward.

As for steering of 96L, as the system and potential weak low associated with 96L are still rather shallow, and as the ULT pulls out, a more west-northwest track by 36 to 52 hours until the vicinity of 64W may be possible, as the ridging synoptics may be enough to allow a slightly more westward movement than indicated by current guidance. Based on the developing and amplifying low in the upper Great Plains, however, I don't think 96L may make it past 70W to 71W at the furthest west potential it may take.

Bottom line: conditions may become more favorable at the middle levels ahead of 96L within the next 36 to 48 hours, allowing gradual development and potentially a bit steadier intensification by 55W to 60W region if the weak low may consolidate more. I also believe 96L may recurve, but a bit further west than indicated by guidance, based on viewing the lower to upper-air synoptics through 74 hours.
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#169 Postby cycloneye » Fri Sep 22, 2006 2:33 pm

DISTURBANCE INVEST (AL962006) ON 20060922 1800 UTC

...00 HRS... ...12 HRS... ...24 HRS... ...36 HRS...
060922 1800 060923 0600 060923 1800 060924 0600

LAT LON LAT LON LAT LON LAT LON
BAMD 12.2N 40.6W 13.3N 41.9W 14.7N 42.8W 15.7N 43.5W
BAMM 12.2N 40.6W 13.0N 41.7W 14.2N 42.7W 15.0N 43.0W
A98E 12.2N 40.6W 12.4N 42.9W 12.8N 45.1W 13.2N 47.0W
LBAR 12.2N 40.6W 13.3N 42.5W 14.9N 44.1W 16.3N 45.6W
SHIP 25KTS 31KTS 38KTS 44KTS
DSHP 25KTS 31KTS 38KTS 44KTS

...48 HRS... ...72 HRS... ...96 HRS... ..120 HRS...
060924 1800 060925 1800 060926 1800 060927 1800

LAT LON LAT LON LAT LON LAT LON
BAMD 16.3N 44.3W 17.2N 47.1W 18.9N 50.8W 21.1N 54.3W
BAMM 15.2N 43.5W 15.5N 45.7W 16.6N 49.9W 17.8N 54.4W
A98E 13.3N 48.6W 14.1N 52.2W 14.7N 56.2W 15.9N 60.5W
LBAR 17.1N 47.1W 19.0N 51.1W 22.3N 55.9W 26.2N 58.6W
SHIP 47KTS 50KTS 55KTS 58KTS
DSHP 47KTS 50KTS 55KTS 58KTS

...INITIAL CONDITIONS...
LATCUR = 12.2N LONCUR = 40.6W DIRCUR = 275DEG SPDCUR = 12KT
LATM12 = 12.0N LONM12 = 38.1W DIRM12 = 277DEG SPDM12 = 13KT
LATM24 = 11.7N LONM24 = 35.7W
WNDCUR = 25KT RMAXWD = 100NM WNDM12 = 25KT
CENPRS = 1010MB OUTPRS = 1013MB OUTRAD = 200NM SDEPTH = M
RD34NE = 0NM RD34SE = 0NM RD34SW = 0NM RD34NW = 0NM

http://twister.sbs.ohio-state.edu/text/ ... s/?C=M;O=D

18:00z Models.

Graphic of Models
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#170 Postby Meso » Fri Sep 22, 2006 3:02 pm

http://www.sfwmd.gov/org/omd/ops/weathe ... orm_96.gif

haha, how's that for spread models? 45 degrees of varience :)
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#171 Postby Sanibel » Fri Sep 22, 2006 3:21 pm

96L appears to be (loosely) spinning up.
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#172 Postby storms in NC » Fri Sep 22, 2006 3:25 pm

I would go with the GFDL if any thing
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#173 Postby Rainband » Fri Sep 22, 2006 3:53 pm

storms in NC wrote:I would go with the GFDL if any thing
I agree. Somewhere between the GFDL and NOGAPS :wink:
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#174 Postby wxman57 » Fri Sep 22, 2006 4:46 pm

There's not as much spread when you remove the extrapolated track, old 06Z and 12Z models, and climo "models". Only the interpreted 18Z NOGAPS takes the system west of 50W before revurving. All major globals recurve much earlier. I still don't see anything significant down near 12-13N, the MLC is the place to focus for development, and that's at 14N-15N. Here are the 18Z models. I even left in the BAM models. Note that the BAMS (shallow steering) is farthest north, indicating that a weaker system might not necessarily track more westward in this case:

Image
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#175 Postby Thunder44 » Fri Sep 22, 2006 5:00 pm

Actually it's hard to track the system after about 3 days because most of the global models this afternoon seem to open it up to a wave or dissapate it. Right now, if anything develops, I don't expect a strong system, wherever it goes.
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#176 Postby WeatherEmperor » Fri Sep 22, 2006 5:01 pm

wxman57, or anybody I have a question. If you look at the model graphic map from wxman57 right above my post, you will see a dark grayish line that should show the track history of 96L. It shows a just north of due west track history. If the models on that graphic are to verify, wouldnt 96L have to move N or NNW at this exact moment? Because it looks that this system has gone inbetween W and WNW since it was declared 96L. What am I seeing wrong? Can anybody explain this to me?

<RICKY>
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#177 Postby wxman57 » Fri Sep 22, 2006 5:07 pm

WeatherEmperor wrote:wxman57, or anybody I have a question. If you look at the model graphic map from wxman57 right above my post, you will see a dark grayish line that should show the track history of 96L. It shows a just north of due west track history. If the models on that graphic are to verify, wouldnt 96L have to move N or NNW at this exact moment? Because it looks that this system has gone inbetween W and WNW since it was declared 96L. What am I seeing wrong? Can anybody explain this to me?

<RICKY>


Yes, that CARQ is the previous track (black line). At least that's where the models have been initialized. I think the focus for development should be much farther north around 14-15N now. In fact, the latest satellite indicates heaviest convection up near 16N-17N along 40W. Good outflow over that area. That would be in line with where the models have been forecasting the system to go. I expect that the models will be initialized much farther north over the next 24 hours.
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#178 Postby MiamiensisWx » Fri Sep 22, 2006 5:11 pm

Thunder44 wrote:Actually it's hard to track the system after about 3 days because most of the global models this afternoon seem to open it up to a wave or dissapate it. Right now, if anything develops, I don't expect a strong system, wherever it goes.


Agreed on your last point, as system's broad circulation may take more time for consolidation around a weak possible LLC location, and as there may be increased shear induced beyond 60 hours due to the middle to upper-level trough eventually progged to exit the Eastern Seaboard by 76 hours and beyond.

By the way, in terms of path, movement, and timing, I'm in the general line of current NOGAPS.
Last edited by MiamiensisWx on Fri Sep 22, 2006 5:13 pm, edited 1 time in total.
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#179 Postby WeatherEmperor » Fri Sep 22, 2006 5:11 pm

Thanks for explaining that for me wxman57. One more quick thing if you have time. Take a look at the 18Z GFS rolling in:

http://www.nco.ncep.noaa.gov/pmb/nwprod ... el_s.shtml

You can see that it takes 96L and recurves it for the reasons you just explained. However, it looks like it develops another low to its south and puts it to near 40W in about 82hrs or so. What do you think this means? Do you think that 96L will split in 2 or is just a totally different feature the GFS is picking up on because its the third run in a row that the GFS has done this

<RICKY>
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#180 Postby wxman57 » Fri Sep 22, 2006 5:18 pm

It's certainly possible that a part of 96L will split off and continue westward. Not that uncommon. But I think the southern part would have a much harder time developing until it reached the western Caribbean Sea and interacts with the stalled front in a week or more.

Here's a satellite shot to indicate where I think the focus for development may be. Note the good outlow (yellow arrows) and increasing convection in the area. Note that it's about 180 miles north of where the 18Z models initialized:

Image
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