ATL: ISAAC - Post-Tropical - Discussion

[cycloneye]

94L likes to avoid the ASCAT passes. Once again another pass is missed. This pass was made around 7:20 PM EDT.

[Weatherfreak000]

I agree ROCK, was this motion expected by the globals? I was thinking more that the significance of this motion could show by allowing 94L to maybe dip under Jamaica. Suppose then it doesn't feel that weakness as strongly and it shoots the Yucatan channel? Tons of uncertainty here still that is for sure...

[MiamiensisWx]

Personal Forecast Disclaimer:
The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products.

I honestly do not understand why the NHC has increased the probability of development within 48 hours to 80%. The system has consistently maintained a poor level of organization all day with little convection with which to strengthen the low-level center. Plus, easterly shear has definitely increased throughout the day due to the building low-level ridge behind the system. The circulation clearly appears to have become even weaker on the latest satellite frames as shear has displaced convection to the west. (Also, the system will encounter more shear in less than a day due to the upper-level low dipping south in front; put on the UL wind overlay and you will see the SW winds.) For two straight days models have shown the system becoming a storm two days later, and the time frame has stayed the same or, in most cases, increased to three days. Only the LGEM and its somewhat less robust pal DSHP mysteriously continue to show a major hurricane, as has always been the case over the past few days, about four days out. Normally, the NHC is rightly conservative and does not raise probabilities, much less upgrade to a TD or TS, without convective organization and support from model trends and/or satellite-derived intensity estimations; a temporary, diurnal-maximum-induced flare-up of convection over night would be insufficient to warrant an upgrade. Nowhere, in either patterns or trends, do I see the continuing organization that the 8 p.m. discussion describes. Due to dry air and shear, neither development nor significant rainfall should occur while the system passes through the northern Windward Islands in about three days.

Also, I strongly believe the models through four days are too far to the north. We have consistently seen over the years that while under a strong low-level ridge, systems whose rate of intensification is overestimated almost always proceed farther south and west than forecasted. As the circulation and its vorticity weaken over the next few days, the system will be increasingly steered by the low-level winds, which are and will remain from NE to SW; just look at the massive low-level subtropical ridge on the CIMSS low-level steering analysis. I see nothing of the north-of-due west movement within 24 hours that the model consensus shows. Instead, by late tomorrow I fully expect a west-southwest track to begin and persist at least until day four. Thus, I think a track well south of Guadeloupe, certainly south of Martinique, and probably just north of Barbados / over Saint Lucia seems most likely. I certainly would not expect anything stronger than 45 mph by that time.

[ROCK]

to put 94L in perspective on how big it is....also you can see the SAL to north wrapping down in front. 20-25 MPH is really fast also.

http://tropic.ssec.wisc.edu/real-time/s ... plitE&time

here is your current steering and it would make sense for a south of due west movment that we are seeing...

http://tropic.ssec.wisc.edu/real-time/d ... oom=&time=

[Aric Dunn]

geez i dislike statistics..

[Riptide]

850mb vorticity has strengthened significantly in the past 3 hours.

[MiamiensisWx]

The preliminary track of the NHC, which would be used if the 94L were upgraded to a TD, is shown on this gridded wind analysis. Note that it shows the system passing south of Hispaniola in five days and failing to become stronger than 40 mph until it reaches the Western Caribbean, on a definitive WNW movement that extrapolates to either TX or LA:

http://www.nhc.noaa.gov/tafb/gridded_marine/ifp/index.php?loop&large&basin=nh2&parm=wind#contents

The solution essentially agrees with my comments from this morning:

http://www.storm2k.org/phpbb2/viewtopic.php?f=59&t=113366&p=2252237&hilit=#p2252237

[wxman57]

The preliminary track of the NHC, which would be used if the 94L were upgraded to a TD, is shown on this gridded wind analysis. Note that it shows the system passing south of Hispaniola in five days and failing to become stronger than 40 mph until it reaches the Western Caribbean, on a definitive WNW movement that extrapolates to either TX or LA:

http://www.nhc.noaa.gov/tafb/gridded_marine/ifp/index.php?loop&large&basin=nh2&parm=wind#contents

The solution essentially agrees with my comments from this morning:

http://www.storm2k.org/phpbb2/viewtopic.php?f=59&t=113366&p=2252237&hilit=#p2252237

I can't see where it says what height that gridded wind analysis is for. Doesn't say if they're surface (10m) winds or 850mb. Could be just straight GFS data, too.

[HurricaneMaster_PR]

Best Track

AL, 94, 2012082000, , BEST, 0, 151N, 406W, 25, 1010, DB, 34

[cycloneye]

00z Best Track

Went up to 15.1N.

AL, 94, 2012082000, , BEST, 0, 151N, 406W, 25, 1010, DB

ftp://ftp.nhc.noaa.gov/atcf/tcweb/inves ... 012.invest

[MiamiensisWx]

The preliminary track of the NHC, which would be used if the 94L were upgraded to a TD, is shown on this gridded wind analysis. Note that it shows the system passing south of Hispaniola in five days and failing to become stronger than 40 mph until it reaches the Western Caribbean, on a definitive WNW movement that extrapolates to either TX or LA:

http://www.nhc.noaa.gov/tafb/gridded_marine/ifp/index.php?loop&large&basin=nh2&parm=wind#contents

The solution essentially agrees with my comments from this morning:

http://www.storm2k.org/phpbb2/viewtopic.php?f=59&t=113366&p=2252237&hilit=#p2252237

I can't see where it says what height that gridded wind analysis is for. Doesn't say if they're surface (10m) winds or 850mb. Could be just straight GFS data, too.

This information is also available from the National Catalog of New and Enhanced Products: http://products.weather.gov/PDD/PDD_Gri ... cial-1.pdf

The Tropical Analysis and Forecast Branch (TAFB) is providing on an experimental basis five (5) day forecasts of gridded Mean Sea Level Pressure, Surface (10-m) winds and significant wave heights. These forecast grids are produced by the marine forecasters using the AWIPS Graphical Forecast Editor (GFE) software and are currently experimental.

There are two grid domains (Atlantic and East Pacific) for the marine weather elements posted on the web site.

The Atlantic grid encompasses the Atlantic Ocean, Caribbean Sea and the Gulf of Mexico with an approximate lower left boundary of 2.9N103W and an approximate upper right boundary of 35N10.5E which covers the TAFB Atlantic Area of responsibility (AOR) from 07N to 31N between 35W and 100W. This grid also provides coverage for western Africa in the event routine forecast data becomes available for geographic region at a future date.

The East Pacific grid encompasses the northeast and southeast Pacific Ocean with an approximate lower left boundary of 20S145W and an approximate upper right boundary of 32.5N65.5W which covers the TAFB East Pacific AOR.

The gridded elements consist of Mean Sea Level Pressure (MSLP) in millibars (mb), surface (10-m) winds in knots (kt) and significant wave heights in feet (ft). These elements are available at a spatial resolution of 12.5 km and a temporal resolution of six (6) hours out to 120 hours or five (5) days for both basins.

Presently, point-and-click marine forecasts are only available within the Coastal Waters Forecast areas of local NWS Weather Forecast Offices. For example, a user can obtain a gridded marine forecast by accessing the main page of a local Weather Forecast Office, such as Miami at http://www.srh.noaa.gov/mfl/ and clicking a point adjacent to the coastline.

Alternatively, a user may craft a URL and enter a specific latitude/longitude point such as the following:

http://forecast.weather.gov/MapClick.ph ... &lon=-80.0

If the specified latitude/longitude point lies within the Coastal Waters Forecast domain, the user is presented with a gridded marine forecast.

NHC's long term goal (2 to 3 years) is to provide point-and-click marine forecasts over the open Atlantic and Pacific oceans and also to provide the data in the NWS National Digital Forecast Database (NDFD). These point-specific forecasts are based upon forecast grids; hence the name "gridded marine forecasts".

Before NHC can provide the gridded forecasts operationally several software upgrades, computer programming tasks, forecaster training sessions, and full backup capability must be completed.

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

I would think that the NHC would use the mean as its track, but I could be wrong.

[Hurricaneman]

00z Best Track

Went up to 15.1N.

AL, 94, 2012082000, , BEST, 0, 151N, 406W, 25, 1010, DB

ftp://ftp.nhc.noaa.gov/atcf/tcweb/inves ... 012.invest

I'm going to completely disagree with best track here, this is closer to 14.5N

Personal Forecast Disclaimer:
The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products.

[wxman57]

Microwave imagery indicates a center closer to 15N - but it really makes no difference at this point.

[gatorcane]

Steering that should steer 94L for the next 5 days...

Note: this image shows the steering at a single point in time only

[cycloneye]

Microwave imagery indicates a center closer to 15N - but it really makes no difference at this point.

Do you have that image?

[Hurricaneman]

Microwave imagery indicates a center closer to 15N - but it really makes no difference at this point.

So that thing going WSW isn't the main low, just an eddy around a larger circulation or possibly a major decouple

Personal Forecast Disclaimer:
The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products.

[cheezyWXguy]

00z Best Track

Went up to 15.1N.

AL, 94, 2012082000, , BEST, 0, 151N, 406W, 25, 1010, DB

ftp://ftp.nhc.noaa.gov/atcf/tcweb/inves ... 012.invest

I'm going to completely disagree with best track here, this is closer to 14.5N

Personal Forecast Disclaimer:
The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products.

yeah Ive been staring at the loops trying to see something at 15.1N, but I just dont. Its hard to say for sure since its nighttime and were looking for low cloud elements, but the turning seems to centered somewhere around 14-14.5 N.

For those of you saying it has "the look," I agree. This thing has a large and fairly vigorous circulation for a tropical wave. I hate to drop big names as they often start hype, but I remember watching Dean in his formative stages. Just like 94L, Dean was a large and broad, but vigorous circulation until he really got going east of the islands. Obviously, this is not meant to say that this is the next Dean, but I do see similarities in structure and size of 94L, as well as environment, to Dean when he was just forming. Someone feel free to tell me I'm wrong.

[HurricaneMaster_PR]

850mb vorticity has strengthened significantly in the past 3 hours.

http://tropic.ssec.wisc.edu/real-time/a ... wg8vor.GIF

Here's the java movie that shows how the vorticity has improve.

http://tropic.ssec.wisc.edu/real-time/a ... rjava.html

[MiamiensisWx]

Microwave imagery indicates a center closer to 15N - but it really makes no difference at this point.

Do you have that image?

Is it this one?

[SouthDadeFish]

Here is a 37 GHz image from Windsat earlier today. 37 GHz is a better representation of the lower levels since 85 GHz is primarily ice scattering.



And here is the 37 GHz color: