ATL: ISAAC - Post-Tropical - Discussion

[cycloneye]

12z Best Track

Continues at a fast pace moving west at 16kts.

AL, 94, 2012081912, , BEST, 0, 144N, 362W, 25, 1011, DB

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

Checking the 06z vs the 12z speed,it has slowed a tad from 20kts to 16kts.

[hurricanes1234]

Is 94L looking a bit opened? Or is it just me?

_____________
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.

[rainstorm]

it has simply gotten too far north and now its gulping very dry dusty air. will be interesting to see if any convection is left in a few hours.

[Hurricaneman]

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 think that the low at 12N 47.5W is sucking all the moisture out of this and basically canibalizing this

[pgoss11]

The wave southwest of 94L seems to be stealing some moisture from 94L. I am very curious if this wave southwest will develope. There is a lot of dry air with 94L being as far north as it is. Looks like it will struggle for awhile.
Not an official forecast.

[rainstorm]

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 think that the low at 12N 47.5W is sucking all the moisture out of this and basically canibalizing this

theoretically they should be far enough apart for both to develop, but conditions arent good enough for that. the low at 12n 47.5 west is in a far more favorable location than 94L.

[perk]

it has simply gotten too far north and now its gulping very dry dusty air. will be interesting to see if any convection is left in a few hours.

Looking at the WV loop it appears to have enough moisture to work with.

[ouragans]

Checking the 06z vs the 12z speed,it has slowed a tad from 20kts to 16kts.

I was about to tell you that. 16kts since 06z, and 18kts since 00z. 94L is on a 270 deg since last position. I'm pretty unquiet for us first, then for you cycloneye

With the overall conditions, I'll start checking for a renumber later this afternoon

[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 think the uncertainties are being greatly exaggerated. The most reliable intensity models which now form the consensus have been consistently trending downward in their forecasts, excepting the LGEM, which continues to show a major hurricane, but only after three days (the same time period it showed two days ago, meaning the model has kept pushing back the time line for intensification). Practically all the models now show only a strong tropical storm as late as seven days out. People are getting too hung-up on the temporary satellite appearances. Last night, the talk was about how great the system supposedly looked. Well, the fact is that most storms usually look great during the diurnal maximum when lapse rates are steepest. Predictably, better organization of the low meant the circulation would draw in more of the stable, dry air mass to its north. The Saharan Air Layer is going to be a serious problem over at least the next four days as a heat ridge building off Africa causes the system to speed up and ingest more dry desert air. (And where there is dusty air, there is almost always wind shear due to enhanced easterlies preventing the center from organizing.) Along with a TUTT low the system will encounter starting in three days, the sheared, SAL-infested environment is what the models are seeing, thereby causing them to show a much weaker system, probably 50 mph or less, passing through the Lesser Antilles in about three and a half days.

Look at all the stratocumuli stretching across most of the basin...they show just how stable the Atlantic is:

http://www.ssd.noaa.gov/goes/east/natl/vis.jpg

Due to the weakness of the system, no one should be surprised that the overwhelming model trend over the past few days - including all the GFS and ECMWF ensembles, the reliable operational models, and even less reliable models like the BAMD and BAMS suites - has been faster and farther southwest by day four and beyond. Given the likely weakness of the system, according to climatology a track south of, rather than over or north of, Hispaniola is increasingly likely. Now most of the ensembles, day five and beyond, are trending as far west as FL and the eastern Gulf, and the consensus in four days is south of Hispaniola, so given further reductions in the intensity forecasts, expect the southwesterly trends to continue. In my view, this system will not develop into a strong TS by the time it crosses the dry graveyard of the Atlantic / Eastern Caribbean and enters the more unstable, reduced-shear environment just east of the Yucatán peninsula. Think Ernesto redux, only perhaps this time posing a much greater threat to the northwestern Gulf (TX / LA). And as this system will be entering the Gulf in the prime of the season, climatology would strongly suggest that hurricane growth is quite possible after day seven. The Gulf looks more like the real target at this stage.

[Blown Away]

12z Best Track

Continues at a fast pace moving west at 16kts.

AL, 94, 2012081912, , BEST, 0, 144N, 362W, 25, 1011, DB

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

Checking the 06z vs the 12z speed,it has slowed a tad from 20kts to 16kts.

23 to 18 mph, 94L is now setting up to develop IMO. Convection popping and wrapping from the NW, it just has the look now!
http://www.ssd.noaa.gov/goes/east/tatl/loop-wv.html

[cycloneye]

Closed circulation? Well,this 41026 bouy has data of SW,WSW and West Winds.

http://www.ndbc.noaa.gov/station_page.php?station=41026

[Gustywind]

Checking the 06z vs the 12z speed,it has slowed a tad from 20kts to 16kts.

I was about to tell you that. 16kts since 06z, and 18kts since 00z. 94L is on a 270 deg since last position. I'm pretty unquiet for us first, then for you cycloneye

With the overall conditions, I'll start checking for a renumber later this afternoon

You're right Ouragans , i noticied that too. By the way, don't forget your friends . We always hope a message or an email from you as we're in the peak of the hurricane season. We wil be glad to share with you your enthusiasm and your passion for the Ouragans . You have to play right now, come aboard en el avion de los huracanes

[Shuriken]

I think that the low at 12N 47.5W is sucking all the moisture out of this and basically canibalizing this

theoretically they should be far enough apart for both to develop, but conditions arent good enough for that. the low at 12n 47.5 west is in a far more favorable location than 94L.

I'm starting to think they're going to merge, although I wouldn't care to gamble at this point on which center ends up being dominant.

http://www.ssd.noaa.gov/goes/east/catl/flash-vis.html

[wxman57]

94L continues to struggle in the hostile conditions that prevail east of the Caribbean this season. It's clear that some of the models (GFS in particular) were incorrect in their assessments of development potential east of the Caribbean. Ernesto and Seven/Helene had a hard time consolidating east of the Caribbean, and 94L will probably also struggle. It appears unlikely that it will be a hurricane when it reaches the eastern Caribbean. Possibly a TS.

[FireBird]

I'm definitely keeping my eyes on both the lows out there. Lots of moisture at the lower latitudes and fairly free of SAL.
Curious to see whether the 12N would develop apart from the ITCZ.
In any case, it's not that I want the rains. We're still cleaning up after last weeks devastating floods.
I just wanna be prepared for anything outta the ordinary...


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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.

[SoupBone]

94L continues to struggle in the hostile conditions that prevail east of the Caribbean this season. It's clear that some of the models (GFS in particular) were incorrect in their assessments of development potential east of the Caribbean. Ernesto and Seven/Helene had a hard time consolidating east of the Caribbean, and 94L will probably also struggle. It appears unlikely that it will be a hurricane when it reaches the eastern Caribbean. Possibly a TS.

What are your thoughts beyond that? Are you thinking a possible east coast threat? Seems like it has a small window of opportunity to get pulled but the conditions in the Gulf of Mexico seem more favorable than they were for Ernesto and Helene.

[cycloneye]

This morning's discussion of 94L by Dr Jeff Masters.

A tropical wave (Invest 94L) located midway between the Lesser Antilles Islands and the coast of Africa is headed west at 20 - 25 mph. This storm is a threat to develop into a tropical storm that will affect the Lesser Antilles Islands as early as Wednesday. The storm is under light wind shear of 5 - 10 knots, and is over waters of 27°C. A large area of dry air lies just to the north of 94L, as seen on the latest Saharan Air Layer (SAL) analysis and water vapor satellite loops. This dry air is interfering with development, and this morning's visible satellite loop shows that 94L's heavy thunderstorm activity is a bit sparse. The storm does have an impressive amount of spin at middle levels of the atmosphere, though. A pass from the Indian OceanSAT-2 satellite Saturday night at 10:06 pm EDT noted a broad, elongated center of nearly calm winds several hundred miles in diameter at the surface, and nothing resembling a well-organized closed surface circulation. 94L will pass near buoy 41041 on Monday morning. The first hurricane hunter mission into 94L is scheduled for Tuesday afternoon.

Forecast for 94L

The latest 8 am EDT run of the SHIPS model predicts that wind shear will be low, 5 - 10 knots, and ocean temperatures will be near 27°C through Monday, then warm to 28°C by Tuesday night. As is typical with storms making the crossing from Africa to the Antilles, dry air to the north will likely interfere with development, and the SHIPS model predicts increased dry air as 94L approaches the Lesser Antilles on Wednesday. However, with shear expected to be low, dry air may be less of an issue for 94L than it was for Ernesto or TD 7. Our two best performing models--the GFS and ECMWF--have both been taking 94L through the Lesser Antilles with every run for the past 36 hours. Both models continue to agree on the timing, with 94L arriving Wednesday night or Thursday morning. The BAMM model, which performed as well as the ECMWF and GFS at 5-day forecasts in 2011, is showing a track just north of the Lesser Antilles. Given this agreement among our top three models for long-range forecasts, I give a 60% chance that 94L will pass through the Lesser Antilles. In their 8 am EDT Tropical Weather Outlook, NHC gave 94L a 60% chance of developing into a tropical depression by Tuesday morning. The GFS model has backed off on its forecast that 94L will develop into a hurricane before reaching the islands, and is now predicting 94L will be a tropical storm with 40 - 50 mph winds at that time. The ECMWF model does not develop 94L. It is unlikely that 94L will be able to organize quickly enough to become anything stronger than a Category 1 hurricane before reaching the islands, given the storm's current struggles with dry air, and the lack of model support for intensification. With 94L staying relatively weak and disorganized, the chances of it turning to the northwest and missing the Lesser Antilles, as the NOGAPS model has been predicting, are diminishing. The GFS model predicts that 94L will go on to hit the Dominican Republic as a strong tropical storm on Friday, though the storm could also miss the island, passing just to the north or the south. At longer ranges, the storm is capable of going anywhere from Canada to Mexico's Yucatan Peninsula; it's too early to tell.

[Portastorm]

What an insightful, educational and well written post! I really enjoyed reading this ... although I didn't enjoy the bit about a potential NW Gulf threat down the road. Nevertheless, I just want to point this out to our non-pro met types that this is a very good example on how one makes a fact-based statement around here. Good work, 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 think the uncertainties are being greatly exaggerated. The most reliable intensity models which now form the consensus have been consistently trending downward in their forecasts, excepting the LGEM, which continues to show a major hurricane, but only after three days (the same time period it showed two days ago, meaning the model has kept pushing back the time line for intensification). Practically all the models now show only a strong tropical storm as late as seven days out. People are getting too hung-up on the temporary satellite appearances. Last night, the talk was about how great the system supposedly looked. Well, the fact is that most storms usually look great during the diurnal maximum when lapse rates are steepest. Predictably, better organization of the low meant the circulation would draw in more of the stable, dry air mass to its north. The Saharan Air Layer is going to be a serious problem over at least the next four days as a heat ridge building off Africa causes the system to speed up and ingest more dry desert air. (And where there is dusty air, there is almost always wind shear due to enhanced easterlies preventing the center from organizing.) Along with a TUTT low the system will encounter starting in three days, the sheared, SAL-infested environment is what the models are seeing, thereby causing them to show a much weaker system, probably 50 mph or less, passing through the Lesser Antilles in about three and a half days.

Look at all the stratocumuli stretching across most of the basin...they show just how stable the Atlantic is:

http://www.ssd.noaa.gov/goes/east/natl/vis.jpg

Due to the weakness of the system, no one should be surprised that the overwhelming model trend over the past few days - including all the GFS and ECMWF ensembles, the reliable operational models, and even less reliable models like the BAMD and BAMS suites - has been faster and farther southwest by day four and beyond. Given the likely weakness of the system, according to climatology a track south of, rather than over or north of, Hispaniola is increasingly likely. Now most of the ensembles, day five and beyond, are trending as far west as FL and the eastern Gulf, and the consensus in four days is south of Hispaniola, so given further reductions in the intensity forecasts, expect the southwesterly trends to continue. In my view, this system will not develop into a strong TS by the time it crosses the dry graveyard of the Atlantic / Eastern Caribbean and enters the more unstable, reduced-shear environment just east of the Yucatán peninsula. Think Ernesto redux, only perhaps this time posing a much greater threat to the northwestern Gulf (TX / LA). And as this system will be entering the Gulf in the prime of the season, climatology would strongly suggest that hurricane growth is quite possible after day seven. The Gulf looks more like the real target at this stage.

[jinftl]

That this system will likely be on the weaker side (invest-td-ts at most) over the next few days actually should be of greater concern to folks here in the U.S., Cuba, Yucatan, Hispanola. If conditions become more favorable for development in the generally much more favorable Western Caribbean, we may have a storm to track that made it past 60W south of 20N because it wasn't a strong system that would be more influenced by troughs.

Separate the model runs from the system. Buying into a model run solution that, to be honest, is not really understood completely by most non-pro mets (myself included), especially ones a week or more out for a system that has no LLC, is a setup for the 'what happened, this season sucks' feeling we go through for pretty much each storm.

94L hasn't fizzled - it never developed into more than a promising wave so there was little to fizzle. Convection pulses and wanes for weak systems.

It's the model runs that are the cause of the frustration because they change so much but as soon as we see the model run we are excited by, we expect that the system will be at that spot and intensity 168 hours or more out and anything less is 'this season sucks'. A day out, the probability of Gordon becoming a Cat 2 was 3%. He may have even hit the Cat 3 thresold (if reanalysis is done, if not he was 1 mph away). And that was ONE day out and no one saw that coming.

94L is probably saying, 'what the heck, i don't even know how to walk yet, and people are talking about whether my name will be retired - if i get named'!!! (invests do sometimes talk.... )

[Riptide]

That this system will likely on the weaker side (invest-td-ts at most) over the next few days actually should be of greater concern to folks here in the U.S., Cuba, Yucatan, Hispanola. If conditions become more favorable for development in the generally much more favorable Western Caribbean, we may have a storm to track that made it past 60W south of 20N because it wasn't a strong system that would be more influenced by troughs.

Separate the model runs from the system. Buying into a model run solution that, to be honest, is not really understood completely by most non-pro mets (myself included), especially ones a week or more out for a system that has no LLC, is a setup for the 'what happened, this season sucks' feeling we go through for pretty much each storm.

94L hasn't fizzled - it never developed into more than a promising wave so there was little to fizzle. Convection pulses and wanes for weak systems.

It's the model runs that are the cause of the frustration because they change so much but as soon as we see the model run we are excited by, we expect that the system will be at that spot and intensity 168 hours or more out and anything less is 'this season sucks'. A day out, the probability of Gordon becoming a Cat 2 was 3%. He may have even hit the Cat 3 thresold (if reanalysis is done, if not he was 1 mph away). And that was ONE day out and no one saw that coming.

94L is probably saying, 'what the heck, i don't even know how to walk yet, and people are talking about whether my name will be retired - if i get named'!!! (invests do sometimes talk.... )

Good call, and it looks fine to me and could develop as the NHC says; within 48 hours. A good sign for developements is the slower forward speed.