Disturbance 90L close to tropical depression strength; TD 2 may rise again

By: Dr. Jeff Masters , 2:02 PM GMT on August 14, 2009

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A strong tropical wave (90L), with a large circulation and a moderate amount of heavy thunderstorm activity, is a few hundred miles southwest of the Cape Verdes Islands, off the coast of Africa. This morning's QuikSCAT pass shows that 90L has a large circulation, but this circulation is not yet well-formed, as it is elongated along an east-west axis. Satellite imagery from the European METEOSAT satellite show that the heavy thunderstorms associated with 90L are gradually becoming better organized, with some spiral banding evident on the south side of the storm. Satellite intensity estimates from NOAA already put 90L at tropical depression strength with 30 mph winds, but the storm does not yet have a well enough formed circulation to be classified as a depression. Water vapor imagery shows that since 90L is forming several hundred miles south of the dry air of the Saharan Air Layer (SAL), the storm should not be affected by dry air and dust as much as Tropical Depression Two was. However, there is some dry air from the SAL being sucked into the circulation of 90L, and this is retarding its development.

Wind shear is moderate, about 10 - 15 knots, but is forecast to fall to the low range, 5 - 10 knots, later today. Shear is then forecast to remain low for the next five days. Sea Surface Temperatures are about 28°C, and will remain in the 27 - 28°C range the next five days. The combination of low wind shear and sufficiently warm SSTs should allow 90L to develop into a tropical depression by Saturday, and potentially reach hurricane strength by Wednesday. Most of our reliable models strengthen 90L into a hurricane by Wednesday, when the storm is expected to be near the northern Lesser Antilles Islands. One important outlier is the ECMWF model, which has 90L passing to the north of the islands, and eventually recurving out to sea east of Bermuda. The ECMWF was by far the most reliable model for forecasting hurricane tracks last year. However, all of our models are pretty unreliable going out 5 days in advance for systems that have yet to reach tropical depression strength. Once 90L becomes a tropical depression and develops a well-formed circulation, the models will have a better handle on forecasting where it will go.


Figure 1. The remnants of Tropical Depression Two (left side of image) and tropical wave 90L (right side of image).

Tropical Depression Two may come back
Tropical Depression Two died yesterday, but may rise again. Satellite loops of the remnants of the storm show that heavy thunderstorms are again attempting a comeback near the axis of what is now a tropical wave. However, dry air continues to interfere with the development of the thunderstorm activity, and moderately high wind shear of 15 - 20 knots is also inhibiting the process. Wind shear over the remnants of TD 2 is expected to remain in the moderate range, 10 - 20 knots, over the next four days. Sea Surface Temperatures (SSTs) are 27°C, but will warm to 28°C two days from now. There is plenty of dry, stable air from the Saharan Air Layer (SAL) to the north and west that will continue to cause the storm problems. The relatively cool SSTs and dry air mean that any re-development of the storm will be slow to occur. NHC has given the system a medium (30 - 50% chance) of becoming a tropical depression again by Sunday morning. Only one reliable model, the NOGAPS, is predicting regeneration of TD 2. The NOAA Hurricane Hunters are flying research missions into the remnants of TD 2 today and Saturday.

I'll have an update Saturday morning, or earlier, if significant developments occur.

Jeff Masters

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So the NHC at this point appears to be leaning towards the "just north of PR" idea.
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Quoting Patrap:
That Depend Hanna,I believe they can Stage in The Leewards for extended Atlantic Flight,maybe St Croix..but Im not sure as too the Range. I think there is a Longitude threshold Point for that

ok - thanks Pat - just curious.
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Quoting LBAR:
90L seems to be fighting itself. Firing 2 different clusters of storms, but not being able coalesce under either of them.


Huh? there is just the main cluster and the bands to the south.
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Quoting Drakoen:


If TD2 manages to regenerate it could be problematic. I'm more concerned with something that is 5 days away than something that is almost 10 days away.


Ditto
Member Since: June 29, 2007 Posts: 0 Comments: 1136
1080. Drakoen
Be on your guard guys. AVG is picking up some Trojans
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The HPC in consultation with the NHC is forecasting 90L to be just north of PR by Day 7..forecast came out 20 minutes ago...


http://www.hpc.ncep.noaa.gov/medr/day7nav.html
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Quoting hurricanehanna:
Hey Pat - question. Once a system is declared a TD or TS, how close in does it have to be for the HH to go investigate?


I'm not Pat, but it tends to be around 50-55W, whilst flying from PR.
Member Since: August 23, 2008 Posts: 7 Comments: 5300
Can someone give me the link to the Statistical Hurricane Intensity Prediction Scheme (SHIPS) model.
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1076. Drakoen
Quoting WxLogic:
12Z ECMWF ... just like NOGAPS in regards TD2 Remnants and bringing it into FL and like it was mentioned before is shifting little by little west but still re-curving it as it approaches the Leeward Islands.


If TD2 manages to regenerate it could be problematic. I'm more concerned with something that is 5 days away than something that is almost 10 days away.
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1075. LBAR
90L seems to be fighting itself. Firing 2 different clusters of storms, but not being able coalesce under either of them.
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1074. Patrap
That Depend Hanna,I believe they can Stage in The Leewards for extended Atlantic Flight,maybe St Croix..but Im not sure as too the Range. I think there is a Longitude threshold Point for that
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Hey all,

I'll be changing my account name since it's long over due...time to have something a little bit more appropriate. I can't post until my account is 12 hours old apparently but when I get back on I'll be "HuracanKY."
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Watch out SFL for 02L:
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1071. viman
Quoting Cotillion:


What specifically do you need?

just basically the coordinates, estimate pressure, direction and distances and such, I started logging the information only when it was at TD status and I regretted that I just didn't do it from the beginning.
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1070. WxLogic
12Z ECMWF ... just like NOGAPS in regards TD2 Remnants and bringing it into FL and like it was mentioned before is shifting little by little west but still re-curving it as it approaches the Leeward Islands.
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Quoting hurricanehanna:
Hey Pat - question. Once a system is declared a TD or TS, how close in does it have to be for the HH to go investigate?


Has to get around I believe 50W for the HH's to go in. They went in though to Dean while it was 53W.
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Quoting disneyfaninnawlins:

The water sat in our house for days and they wouldn't allow us back in for almost two weeks after the hurricane hit so taking them down asap was not an option. I did invest in the hurricane proof windows when we rebuilt. I just hope they really work for the money that we spent. :)

In that kind of situation, and with Katrina... I don't think the boards were to blame. There are some things you just can't prevent. Once the water gets in, it won't get out without human intervention, aside from normal evaporation.
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Shucks. I need to step out for a while. I really want to do some more looking at this TD 2. I'm remembering that Andrew had some problems getting going, which didn't impede later development once it got into a more favorable environment.

I'll check in later when I can actually look as some of the links u guys are slinging around.
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Convection really starting to fire off over 90L, now to see if it can cover the COC and the ciruclation tightens up some we might have a TD by 11 Am tomorrow.


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14/1745 UTC 14.7N 43.4W T1.0/1.0 02L

14/1745 UTC 11.7N 29.0W T1.5/1.5 90L
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Hey Pat - question. Once a system is declared a TD or TS, how close in does it have to be for the HH to go investigate?
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1062. Myakka
Quoting Greyelf:


IE user here on multiple computers. No problems, no hitches, no freezes (but I haven't since all this virus talk started either). There's obviously something else causing problems.


Web Developer here (11 years), no issues with the blog whatsoever. People, get an anti-virus app, and a spy-ware blocker and call it good. Now back to weather...
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1061. Thaale
Quoting jeffs713:

Boarding up is good for stopping most projectiles, but the boards should be removed ASAP after the storm, to allow for ventilation.
Boarding up will not stop something like the point of a 4x4 plowing through at 100mph, but the chances of that particular situation happening is somewhat slim.

A better option is to get hurricane windows, as they have a clear plastic layer between two sheets of glass, and they *will* stop a 4x4. (they will also prevent break-ins).
Yeah, but I've heard that hurricane windows may not breach even during a cat 5, but they and/or their frames do get all warped, scratched up, and permanently scarred if you let them go through a storm unprotected. Basically you have to then start over with a new set of $8000 windows. I don't know if this is still true or if the materials have gotten better of late or what - if anyone can contradict, please do. I do know that I don't see anyone with the resources to pick amongst various options choosing to go with just impact-resistant hurricane windows.

I do agree with you that the 100 mph spear-impact scenarios are very unrealistic. Isn't the Dade County standard something like, able to withstand a 2x4 at 34 mph? Even a 150 mph wind doesn't necessarily accelerate every heavy object it picks up TO 150 mph!
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1060. Drakoen
Quoting IKE:


Through the Caribbean.


That's not in the Caribbean
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Quoting jeffs713:

Boarding up is good for stopping most projectiles, but the boards should be removed ASAP after the storm, to allow for ventilation.
Boarding up will not stop something like the point of a 4x4 plowing through at 100mph, but the chances of that particular situation happening is somewhat slim.

A better option is to get hurricane windows, as they have a clear plastic layer between two sheets of glass, and they *will* stop a 4x4. (they will also prevent break-ins).

The water sat in our house for days and they wouldn't allow us back in for almost two weeks after the hurricane hit so taking them down asap was not an option. I did invest in the hurricane proof windows when we rebuilt. I just hope they really work for the money that we spent. :)
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Quoting Greyelf:


IE user here on multiple computers. No problems, no hitches, no freezes (but I haven't since all this virus talk started either). There's obviously something else causing problems.

My work computer is using IE6 (yes, we are in the stone age still), and I'm not having any problems, other than the page loading slowly (as usual, since we have 350ish users on a pair of T1 lines)
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Quoting viman:
Question for anyone: Where can I find the old Invest information for TD#2? Is it achived anywhere and is it accessible? Thanks


What specifically do you need?
Member Since: August 23, 2008 Posts: 7 Comments: 5300
1055. JLPR
So two Tropical systems for the Northern islands

that sucks! =|

I hope they both dissipate
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1053. Greyelf
Quoting StormChaser81:


The blog crashes my internet explorer every time I use it. I have to use firefox to use the blog now, just a update for all of you weather lovers. Some is happening with this blog.


IE user here on multiple computers. No problems, no hitches, no freezes (but I haven't since all this virus talk started either). There's obviously something else causing problems.
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1052. viman
Question for anyone: Where can I find the old Invest information for TD#2? Is it achived anywhere and is it accessible? Thanks
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LOL i was thinking the same thing
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Big burst of convection around 30W and 14N:
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Afternoon, everybody.

I'm back in the S. Florida area after a few weeks on vacation, mainly out in the inter-mountain West of the US.

I'm noting that tomorrow is 15 Aug, which was my cutoff date for no formation. I'm very pleased to see that my "forecast" (not that it was really one, more like an educated guess at best) turned out to be correct. I kinda bet on nothing forming when I made my vacation plans, and I would have been highly upset if there had been serious action in the ATL and I was stuck in, say, Denver.

By Sunday I should be back at my house, which will make me a lot more comfortable about seeing storms come up.

Is kman back yet? I know I have a lot of "back-reading" to do to catch up on our two potential systems.....
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Quoting WeatherStudent:


???, that was a contradiction, are you OK? I'd assume not.

No, it wasn't a contradiction. What FloridaTigers is saying is just that a week out, models are pretty useless for exact track information. Think about Ike last year. 5-7 days out, the models were forecasting recurvature and a SE FL strike. We know how that ended up.
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1046. fmbill
Quoting jeffs713:

NHC isn't posting advisories on it. All of the WU "current" and "historical" data is straight from the NHC.


NHC has it as an AOI.

SFWMD still has the model runs being updated.

Even the Navy site still has it up and they are still updating the data.

Oh well...there are many other places to get the info provided on these systems...it just seems it would be here, too.
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90L is getting a little better in its organization, there seems to be a little sheer from the south east keeping the convection on the northwestern side of the circulation. Once the sheer dies down it looks to intensify really fast.
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Until we get a named system, we've got nothing but media hype and phantom storms kicked up by all of the computer models. The Saharan dust and El Nino is kicking this season in the butt so far**** 17N and 55 W research purposes?? Old TD 2 appears to have 9 lives.
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12Z ECMWF: Stormfest in the Atlantic
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From the model data file for 90L

AL 90 2009081412 03 OFCL 0 121N 265W 25
AL 90 2009081412 03 OFCL 12 121N 289W 30
AL 90 2009081412 03 OFCL 24 121N 314W 35
AL 90 2009081412 03 OFCL 36 121N 340W 40
AL 90 2009081412 03 OFCL 48 123N 372W 45
AL 90 2009081412 03 OFCL 72 135N 440W 60
AL 90 2009081412 03 OFCL 72 135N 440W 60
AL 90 2009081412 03 OFCL 96 150N 505W 75
AL 90 2009081412 03 OFCL 120 170N 575W 90


Interpolated at 18Z

AL 90 2009081418 03 OFCI 0 125N 288W 25
AL 90 2009081418 03 OFCI 12 125N 313W 30
AL 90 2009081418 03 OFCI 24 125N 338W 35
AL 90 2009081418 03 OFCI 36 126N 367W 40
AL 90 2009081418 03 OFCI 48 130N 400W 46
AL 90 2009081418 03 OFCI 60 136N 434W 53
AL 90 2009081418 03 OFCI 60 136N 434W 53
AL 90 2009081418 03 OFCI 72 143N 467W 61
AL 90 2009081418 03 OFCI 72 143N 467W 61
AL 90 2009081418 03 OFCI 84 150N 500W 68
AL 90 2009081418 03 OFCI 96 159N 534W 76
AL 90 2009081418 03 OFCI 108 169N 568W 83
AL 90 2009081418 03 OFCI 120 180N 604W 91
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Quoting Thaale:
Yeah, but it's been the best model all year (and wasn't it pretty good last year?), and BTW it's usually better with undeveloped systems anyway. Consensus science is bad science; you don't ignore the model with the best track record just because it's an "outlier." And you should take with a healthy dose of skepticism the GFS when it's projecting future movements of what's still nothing more than a low. Once there's an actual storm for them to project the future track of, the GFS and GFDL will have more reliability.



just because it has the best track record doesn't necessarily mean it has a good handle on this storm. ECMWF tends to amplify troughs much more aggressively compared to any other model and right now it is a huge outlier. The CMC which has greatly improved this year is very good at one thing which is forecasting troughs and it does not predict a very strong trough but right now the consensus is what should be looked at
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GOMEX / Carribean looks very volatile at the moment.
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The faster foward movement (Thanks Ike for the Update to 15knts) means that TD2 is starting to feel less upper level shear...

You can see this clearly as the weak cirrus shield from fairly limited convection at the present is allowed now to blow off to the east and southeast.

Kinda of neat to watch...

If we were to get more deep convection we could even have a CDO (woops did I say that out loud???)
RGB Loop
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1038. IKE
Quoting Cotillion:
000
WHXX01 KWBC 141843
CHGHUR
TROPICAL CYCLONE GUIDANCE MESSAGE
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1843 UTC FRI AUG 14 2009

DISCLAIMER...NUMERICAL MODELS ARE SUBJECT TO LARGE ERRORS.
PLEASE REFER TO NHC OFFICIAL FORECASTS FOR TROPICAL CYCLONE
AND SUBTROPICAL CYCLONE INFORMATION.

ATLANTIC OBJECTIVE AIDS FOR

DISTURBANCE INVEST (AL902009) 20090814 1800 UTC

...00 HRS... ...12 HRS... ...24 HRS. .. ...36 HRS...
090814 1800 090815 0600 090815 1800 090816 0600

LAT LON LAT LON LAT LON LAT LON
BAMS 12.5N 28.8W 12.6N 32.1W 12.6N 36.1W 12.1N 39.9W
BAMD 12.5N 28.8W 12.8N 31.5W 13.1N 34.7W 13.3N 38.4W
BAMM 12.5N 28.8W 12.7N 31.8W 13.0N 35.4W 12.9N 39.3W
LBAR 12.5N 28.8W 12.7N 32.0W 13.1N 35.8W 13.6N 40.1W
SHIP 25KTS 30KTS 39KTS 51KTS
DSHP 25KTS 30KTS 39KTS 51KTS

...48 HRS... ...72 HRS... ...96 HRS. .. ..120 HRS...
090816 1800 090817 1800 090818 1800 090819 1800

LAT LON LAT LON LAT LON LAT LON
BAMS 11.5N 43.5W 11.5N 48.0W 15.2N 52.7W 18.4N 61.5W
BAMD 13.5N 42.4W 13.7N 49.9W 13.8N 55.3W 15.8N 59.5W
BAMM 12.8N 43.2W 12.3N 49.6W 13.7N 53.5W 17.6N 58.7W
LBAR 14.2N 44.8W 14.4N 52.9W 14.9N 54.5W .0N .0W
SHIP 62KTS 80KTS 92KTS 95KTS
DSHP 62KTS 80KTS 92KTS 95KTS

...INITIAL CONDITIONS...
LATCUR = 12.5N LONCUR = 28.8W DIRCUR = 280DEG SPDCUR = 14KT
LATM12 = 11.8N LONM12 = 25.1W DIRM12 = 283DEG SPDM12 = 14KT
LATM24 = 11.6N LONM24 = 23.2W
WNDCUR = 25KT RMAXWD = 75NM WNDM12 = 25KT
CENPRS = 1007MB OUTPRS = 1011MB OUTRAD = 200NM SDEPTH = M
RD34NE = 0NM RD34SE = 0NM RD34SW = 0NM RD34NW = 0NM

$$
NNNN




Through the Caribbean.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
1036. 100l
I haven't heard any comment about this lately. But what I remember from watching all of the fish storms in '06 is that the earlier they form the more chance they have of being steered out to sea. Since TD2 is not developed now wont that give it a better chance of making it across the Atlantic and could become a problem later?
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One thing to note on 90L from the guidance given to the models, is despite the shear and the current disorganised trend as noted by the NHC, the pressure has actually dropped one millibar.
Member Since: August 23, 2008 Posts: 7 Comments: 5300
Quoting CJ5:
ExTD2 continues to maintain itself today and still could become a threat later on...


The models certainly hint at it. It needs to build upon DMAX.
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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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