TD 2 nearly dead; African disturbance 90L gathering strength

By: Dr. Jeff Masters , 2:38 PM GMT on August 13, 2009

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Tropical Depression Two is near death, but is still worth watching. The dry, Saharan air to the north and west of the depression, combined with moderately high levels of wind shear of 15 - 20 knots, have almost completely destroyed all of TD 2's heavy thunderstorms. Satellite loops of the storm show a well-formed circulation, but almost no heavy thunderstorm activity.

Wind shear over TD 2 is expected to remain in the modereate range, 10 - 20 knots, over the next five days. Sea Surface Temperatures (SSTs) are 27°C, but will warm to 28°C three days from now. There is plenty of dry, stable air from the Saharan Air Layer (SAL) to to TD 2's north and west that will continue to cause the storm problems. The relatively cool SSTs and dry air mean that TD 2 will not be able to intensify quickly, and some of the models indicate the TD 2 may get destroyed in the next day or two. However, several models still predict TD 2 will become a tropical storm. The HWRF model predicts TD 2 will become a hurricane five days from now, but this seems unlikely given the dry air and relatively high wind shear affecting the storm.


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

African tropical wave 90L
A strong tropical wave with a large circulation and plenty of heavy thunderstorm activity is a few hundred miles south of the Cape Verdes Islands, off the coast of Africa. NHC dubbed this disturbance 90L this morning. This morning's QuikSCAT pass shows that 90L has a very large circulation, and top winds of about 30 mph. Satellite imagery from the European METEOSAT satellite show that the heavy thunderstorms associated with 90L are in two major bands, to the north and to the south of the center. There is no heavy thunderstorm activity near the center yet, and this would have to happen before 90L can be named Tropical Depression Three. 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 has been. Wind shear is about 20 knots over 90L, and is forecast to remain in the moderate range, 10 - 20 knots, over the next five days. Sea Surface Temperatures are about 28°C, and will remain in the 27 - 28°C range the next five days, which are high enough above the 26°C threshold for tropical cyclone formation to allow some slow development to occur. The GFS and ECMWF models continue to predict the development of this wave, though they are now less aggressive about intensifying it than they were in earlier runs. The consensus among the reliable HWRF, GFDL, GFS, and ECMWF models is to bring 90L to point near or just north of the northernmost Lesser Antilles Islands 6 - 8 days from now. The storm could be at hurricane strength by then, as forecast by the SHIPS intensity model.

I'll have an update Friday morning.

Jeff Masters

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Quoting Canealum03:
90L actually reminds me very little of Andrew. Remember Andrew was a very small storm. If anything, TD 2 reminds me much more of Andrew: small storm that was struggling to survive.


90L reminds me of either Floyd or Dean.
Member Since: August 10, 2009 Posts: 3 Comments: 672
The new GFS shows the moderate easterly shear over 90L weakening over the next 24 hours...

It shows a modest anti-cyclone building aloft...much smaller than a couple days ago...which is one of the reasons the GFS doesn't forecast quite the intensification.

If this massive storm gets going...I think the anti-cyclone might end up being more like the runs from a few days ago, but I guess we'll see
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Quoting jasoniscoolman10:
wow that is big.1081.8 miles in diameter


Too bad its incorrect. Read above.
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234. LBAR
Looks like TD2 is firing up the cylinders again.
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TD 2 weakens; 90L is trouble
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Looks like TD2 is about to enter an area of lower shear...
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Quoting CaicosRetiredSailor:
Quoting

193. AllBoardedUp 11:33 AM EDT on August 13, 2009

...Before you call me a troll I have been on this site for since 2004, I just don't comment very often.

----------------------------------

I'm impressed, especially since the site didn't exist until 2005!
Off one year, still not bad considering I keep forgetting how old I am.
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90L actually reminds me very little of Andrew. Remember Andrew was a very small storm. If anything, TD 2 reminds me much more of Andrew: small storm that was struggling to survive.
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Quoting CaicosRetiredSailor:
Quoting

193. AllBoardedUp 11:33 AM EDT on August 13, 2009

...Before you call me a troll I have been on this site for since 2004, I just don't comment very often.

----------------------------------

I'm impressed, especially since the site didn't exist until 2005!

It was really underground when he joined.
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TD2 may actually have a thunderstorm attributed to it, but it still seemingly can't put something on its COC. The convection is still to the NW of it.

Though ADT shows it, the visible is clear as day with that.

If it can't build on top of the COC, it ain't going anywhere fast.

Member Since: August 23, 2008 Posts: 7 Comments: 5300
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Look at 90L:
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Quoting

193. AllBoardedUp 11:33 AM EDT on August 13, 2009

...Before you call me a troll I have been on this site for since 2004, I just don't comment very often.

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I'm impressed, especially since the site didn't exist until 2005!
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Quoting hahaguy:


Exactly. The larger a storm is the harder it is to intensify rapidly.


Also the larger the storm the more it can fight off wind shear and dry air, kinda makes it own environment.
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Quoting Acemmett90:

and he didn't know what he was talking and me and cane live in fla so we took offence to his commants
I live in Galveston. I pretty much have a qrasp of what Galveston can endure. We are still rebuilding here and I didn't take offense to it, because I knew how obviously stupid his remarks were. But my point is you all turned around and predicted the end of Nola. I guess people in Nola shouldn't take offense?
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Quoting nrtiwlnvragn:


You have it about 4 times larger than the NHC. From the vital statistics record:

NHC 90L INVEST 20090813 1200 116N 0225W 280 036 1009 1012 0222 13 111 -999 -999 -999 -999 M -999 -999 -999 -999 -9 -99N -999W -999 -999 -999 -999

222 km is the estimated radius of outermost closed isobar, so diameter = 444 km, ~275 miles.
i calculated where the Northern-West band is to Southern-East band is, if that is not what the NHC calculated thats fine.
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Gang - there will not be another Andrew, a Katrina, a Camille, etc...
Each storm has it's own set of properties, dynamics,etc...and it will have it's own name. Let's not start causing panic where it is not needed :)

*steps off soapbox*
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Quoting nrtiwlnvragn:


You have it about 4 times larger than the NHC. From the vital statistics record:

NHC 90L INVEST 20090813 1200 116N 0225W 280 036 1009 1012 0222 13 111 -999 -999 -999 -999 M -999 -999 -999 -999 -9 -99N -999W -999 -999 -999 -999

222 km is the estimated radius of outermost closed isobar, so diameter = 444 km, ~275 miles.




A sane retort is always a Breath of fresh air.
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the models at this time are really not sure with the future of 90L. Unless a proper centre is ascertain they will have difficulty in initialising the system. most shallow systems tend to go with east-west flow. i believe 90L which is so large will take some time to coalesce before it can be a significant tropical entity during that period it will continue west for the next few days. it is also my belief that 90L will be the first name storm
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90L currently looks like a subtropical system, as its highest winds and convection are located far from the center. Eventually, it will consolidate and become a more compact storm (albeit still very large); in order to intensify it will have to do this.
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Hurricane Prep Entry
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Quoting jasoniscoolman10:
lots of red on here.
Jason, what does this map represent, never seen it before.
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Quoting Acemmett90:

the fact that this storm can hit teh keys and still effect the carolina is scary


Any storm could do this. So what. You can't have any idea that a storm is going to do this until it forms, and then gets within 5 days of land. Even then, the error is +/- 300 miles.
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I don't know if 90L can consolidate convection without shrinking in size. Drak, your thoughts? Anyone else?
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Quoting canesrule1:
WOW! i just calculated that 90L is 1081.8 miles in diameter! in comparison Gilbert in 88' was around 800 miles in diameter at peak intensity!


You have it about 4 times larger than the NHC. From the vital statistics record:

NHC 90L INVEST 20090813 1200 116N 0225W 280 036 1009 1012 0222 13 111 -999 -999 -999 -999 M -999 -999 -999 -999 -9 -99N -999W -999 -999 -999 -999

222 km is the estimated radius of outermost closed isobar, so diameter = 444 km, ~275 miles.
Member Since: September 23, 2005 Posts: 14 Comments: 11161
Quoting rwdobson:
actually right now 90l's huge size is working against it, making it harder to get a real spin going. gonna take it a while to get to TD status.

and remember, the margin of error on all these 10 days GFS runs is thousands of miles...


Exactly. The larger a storm is the harder it is to intensify rapidly.
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Quoting canesrule1:
um smart guy im giving facts and opinions, the apocalypse guy was talking garbage.
Nola is history! That's not a fact, especially for a storm that hasn't even developed yet. Who's trying to cause a panic here. Smart guy!
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Quoting P451:



90L


Once convection gets going in the COC we can expect a TD by Saturday.
Member Since: August 10, 2009 Posts: 3 Comments: 672
Quoting AllBoardedUp:
You people just put a guy on the ignore list for doing the same thing. The only difference that I see is that he was joking. And if he wasn't I can't see how such intelligent people on the site would fall for this. Before you call me a troll I have been on this site for since 2004, I just don't comment very often. I try to learn what I can and I really do enjoy this site. But people, take a chill pill.
um smart guy im giving facts and opinions, the apocalypse guy was talking garbage.
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203. Jaxen
Today is the 5-year anniversary of Charley ... I'm in Orlando and got whalloped by that thing ... and then 90L would get near US Coast right around the 24th, the 17th anniversary of Andrew. Add to that I have a 9-mnoth old now, please pardon my general uneasiness now (about a freakin' INVEST).

Historical climatology supports this thing heading to the SE US, with that strong Atlantic ridge and the 1st named storm so late in an El Nino season. Coincidences I hope. And I hope I don't start to worry until I have something to worry about.
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actually right now 90l's huge size is working against it, making it harder to get a real spin going. gonna take it a while to get to TD status.

and remember, the margin of error on all these 10 days GFS runs is thousands of miles...
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199. 7544
Quoting P451:
TD2 with yet another comeback. Seems to have been the story with this system time and again.



yeap the race is on who will get the name ana first 99l or 90l stay tuned this should be fun
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90L will have a harder time strengthening quickly then TD2. Reasoning is the sheer difference in their COC size. TD2 needs to defeat the dry air which seems like its trying to do with the sporadic convection and 90L is trying to strengthen, but with no convection around or near its center it will be hard to do so. Something to watch closely for sure.
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Quoting Acemmett90:

lol
quick tell ws to get off the east coast in all serousness this is bad
yeah, i think the NHC is starting to pee in there pants with the models coming towards us and a huge storm like this.
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StormW is wind shear the only thing you see from keeping developement in the gulf? Also how many shear runs will you have to see before you give it a higher chance than low? Im trying to stay on top of this so it doesnt catch me off guard here on the gulf coast. Thank you for your reports.
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Quoting Acemmett90:

yah it would be the end of nola
You people just put a guy on the ignore list for doing the same thing. The only difference that I see is that he was joking. And if he wasn't I can't see how such intelligent people on the site would fall for this. Before you call me a troll I have been on this site for since 2004, I just don't comment very often. I try to learn what I can and I really do enjoy this site. But people, take a chill pill.
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Quoting Mclem1:
What are the odds we see TD3 today? All that false Ana talk yesterday made my mouth water now I'm very anxious for something to strengthen!
i think TD today is about 40% TD before Saturday 99.99%
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Ana went from a cute little thing to a Big Gal. They need lovin too!
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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.