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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000
NOUS42 KNHC 141400
WEATHER RECONNAISSANCE FLIGHTS
CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.
1000 AM EDT FRI 14 AUGUST 2009
SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)
VALID 15/1100Z TO 16/1100Z AUGUST 2009
TCPOD NUMBER.....09-078

I. ATLANTIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
2. OUTLOOK FOR SUCCEEDING DAY: PSBL LOW LEVEL INVEST
FOR 16/1800Z NEAR 17.0N AND 55.0W ON THE REMNANTS
OF TD-02.
3. NOTE: 1- THE G-IV WILL FLY A RESEARCH MISSION AROUND
THE REMNANTS OF TD-02 TODAY DEPARTING TBPB 14/2000Z.
2- BOTH NOAA43 AND G-IV WILL FLY RESEARCH MISSIONS
IN AND AROUND THE REMNANTS OT TD-02 DEPARTING TBPB
15/2000Z.

II. PACIFIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
2. SUCCEEDING DAY OUTLOOK.....NEGATIVE.
WVW


Member Since: Posts: Comments:
Quoting Acemmett90:

Crap
I've also been noticing a lot of posts that people are saying it will curve in the Gulf, so if that is the scenario SFLA is likely to get bombed with a Category 4+ hurricane and then the gulf states have to monitor. I'm not trying to scare you i'm just telling you the truth.
Quoting canesrule1:
i agree we will probably have a renumber around 1 and a TD at 2.

they won't issue advisories at starting at 2pm if the storm isn't close to land.

it would have to be 11am or 5pm for them to issue advisories if a depression forms.
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3534. eddye
audioslave your not write it looking great right now so stop wishing for that to hapen because it is looking pretty good right now
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Quoting StormW:


Good point kman...the reason we see the flareup of convection is as the dry air is entrained at the lower levels, it cools the surounding atmosphere in the system, basically causing a temporary in crease in the lapse rate, allowing for colder cloud tops. If I'm correct, we should see this collapse soon.


Well,it's been the pattern for the last day or two, fires something up, then it goes, fires up, then it goes... etc.

Storm, the GFS of course has the storm plowing into the Lesser/Greater Antilles without any real recurvature. The Euro curves it before it reaches the top of the Windwards.

Now, both models seem to think the B/A High will be sitting basically over the Azores. But, the GFS has it - seemingly - about 10mb stronger, with a greater forward speed (although the Euro has it going more up, it hasn't reached 60W while the GFS has it on top of Hispaniola. Both at 168hrs.)

Is this speed and pattern variance due to just the trough, or the strength of the high or both? Or indeed, something else.
Member Since: August 23, 2008 Posts: 7 Comments: 5300
Quoting TampaSpin:


Old TD2 has been fighting the Dry air for a long time......the Shear has what has caused it not to take off.....WEll the Shear is much less now.....Take off is coming.

it is in 10kts of shear but as it moves westward it will be going into 5kts wind shear
Member Since: June 13, 2009 Posts: 2 Comments: 12719
3530. WxLogic
Quoting OSUWXGUY:
Good Morning Everybody!

Another August day in the tropics...


Morning...
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It's dealing with the same dry air and easterly shear that TD 2 delt with. It is not protected from shear like some people have said.
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Good Morning Everybody!

Another August day in the tropics...
Quoting BatTracker:
Good morning all!

Loooong time lurker, this place is where I go all the time for the latest and greatest info. Good stuff Storm, Tampa, Orca and the rest of the crew...

Got a question for you all, is it just me or are the models bringing 90L dangerously close to an Hebert box?
lol, yes all models are taking it though the Hebert Box as a major hurricane, so SFLA must watch this very carefully.
Storm - what are the "unfavorable conditions" in the GOMEX that NOAA refers to when discussing the Carribean wave that will be entering the GOMEX shortly? TIA
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Quoting StormW:


Good point kman...the reason we see the flareup of convection is as the dry air is entrained at the lower levels, it cools the surounding atmosphere in the system, basically causing a temporary in crease in the lapse rate, allowing for colder cloud tops. If I'm correct, we should see this collapse soon.


That makes Sence StormW but, Old TD2 has been fighting that and Shear for a long time now....Shear has dropped a ton on it now...will be interesting to see what happens when all it has to fight is just the dry air....
Member Since: September 2, 2007 Posts: 179 Comments: 20448
Quoting CaneHunter031472:
90L looks very well organized on Visible this morning I would not be surprise if it is declared a TD3 by noon.
i agree we will probably have a renumber around 1 and a TD at 2.
Good Morning Folks...On the road on a college road trip (we were in the NE at Harvard/Yale and Boston area this past week) and heading "slowly" back towards Florida and going into Charleston today from Roanoke, VA.

90L looking very good and ominous....Check in in a few days......WW
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Quoting BayouBorn1965:


Wish we could get through with all of our Katrina repairs and PAPERWORK before another bomb. Thank you so much for keeping us informed. Weather Center just doesn't tell enough!

This is a great blog to be on during the season.. you have so many good folks that provide great information on all fronts to keep you up-to-date... :-)
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Quoting BayouBorn1965:


Wish we could get through with all of our Katrina repairs and PAPERWORK before another bomb. Thank you so much for keeping us informed. Weather Center just doesn't tell enough!
yup, same here, I'm definitely not trying to scare you I'm just telling you the truth and the facts, I'm not going to lie, then you let your guard down and then you get bombed with a major hurricane, your welcome btw.
Good morning all!

Loooong time lurker, this place is where I go all the time for the latest and greatest info. Good stuff Storm, Tampa, Orca and the rest of the crew...

Got a question for you all, is it just me or are the models bringing 90L dangerously close to an Hebert box?
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Quoting kmanislander:
Good morning

Here is the big challenge for Ex TD2. From the WV image you will see that it is surrounded by extremely dry air. In particular, there is a significant "tongue" of dry air to the South that is undercutting any moist inflow from that direction and to the West there is only a small barrier of moisture between the low center and bone dry air.

While there is a current resurgence of convection it will soon be hitting the peak heat of the day out there in the next few hours which may put a damper on the comeback attempt.



Old TD2 has been fighting the Dry air for a long time......the Shear has what has caused it not to take off.....WEll the Shear is much less now.....Take off is coming.
Member Since: September 2, 2007 Posts: 179 Comments: 20448
How far does the dry air extend in front of 02? I can't find a satelite showing it far enough.
Member Since: August 22, 2006 Posts: 0 Comments: 1462
3516. LBAR
It's amazing what a couple of degrees of latitude (and longitude) can do for a tropical system!
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90L looks very well organized on Visible this morning I would not be surprise if it is declared a TD3 by noon.
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Quoting Stormchaser2007:


Wrong on every front. Shear is 10 knots. No where near the 30 that was hitting TD2. Also it has a LLC that is elongated and in the convection. The convection is rather strong and all this needs to be classified is for the LLC to become tighter.


I also live in Okeechobee. The right storm comes through and we could have ourselves another Katrinia. The dyke is in horrible condition!
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3512. NEwxguy
Quoting kmanislander:
There have been so many hurricanes over the years that anyone can find a track that matches their current thinking.


I couldn't have said it better
Member Since: September 6, 2007 Posts: 888 Comments: 15989
Quoting KEEPEROFTHEGATE:


our leeward island friends best to keep there heads up for this one
yup, models are saying Category 3 or higher before it reaches the northern Antilles, yikes!
Quoting canesrule1:
so when it passes over southern Florida as some models are hinting Category 4 is almost certain again as models are saying, then over the gulf Category 5 is likely, so lets wait and see.


Wish we could get through with all of our Katrina repairs and PAPERWORK before another bomb. Thank you so much for keeping us informed. Weather Center just doesn't tell enough!
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3509. WxLogic
Quoting KEEPEROFTHEGATE:


our leeward island friends best to keep there heads up for this one


That's for sure.
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Quoting tornadofan:


Sure looks like it is affecting it on the satellite loops, along with dry air.


Looks can be deceiving as we've learned. Stormchaser2007 explained it pretty well.
Member Since: August 10, 2009 Posts: 3 Comments: 672

Have a great Friday everyone.
See ya later.
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Quoting Stormchaser2007:


Wrong on every front. Shear is 10 knots. No where near the 30 that was hitting TD2. Also it has a LLC that is elongated and in the convection. The convection is rather strong and all this needs to be classified is for the LLC to become tighter.
That looks tight enough for me, remember this is based on satellite:
Quoting presslord:
Chuck! Can you please put a stop to this rain for the weekend?!?!?!


Yea, looks pretty soggy, especially with that little wave passing just south of here, may enhance our rain. A lot of it just offshore too. Looks like just rain and nothing severe. Need to watch 90 very closely next week. If I recall, this is close to the Hugo setup. Trough strong enough to pull the system north a little, but not strong enough to recurve out to sea, then the high builds back in and pushed Hugo ashore. Still a long way to go, but the GFS has been trending towards a less amplified trough which is good for us, but unfortunately targets someone else. I DO NOT see 90 going out to sea.
Member Since: August 27, 2006 Posts: 0 Comments: 1785
3504. KEEPEROFTHEGATE (Mod)


our leeward island friends best to keep there heads up for this one
Member Since: July 15, 2006 Posts: 178 Comments: 56141
Quoting canesrule1:
remember 90L has an anticyclone over it right now, shear does not affect it.


Sure looks like it is affecting it on the satellite loops, along with dry air.
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Quoting BayouBorn1965:


Thank you! Can I say "CRAP!"
so when it passes over southern Florida as some models are hinting Category 4 is almost certain again as models are saying, then over the gulf Category 5 is likely, so lets wait and see.
Quoting audioslave8:
90L doesn't look too good right now. Shear is hitting it - the same shear that ripped TD 2 apart. The center is east of the convection. And that convection is still rather weak. I don't think it'll be classified as a TD today unless some major changes occur during the day. And I'm starting to wonder if it'll survive the shear.


Wrong on every front. Shear is 10 knots. No where near the 30 that was hitting TD2. Also it has a LLC that is elongated and in the convection. The convection is rather strong and all this needs to be classified is for the LLC to become tighter.
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Quoting audioslave8:
90L doesn't look too good right now. Shear is hitting it - the same shear that ripped TD 2 apart. The center is east of the convection. And that convection is still rather weak. I don't think it'll be classified as a TD today unless some major changes occur during the day. And I'm starting to wonder if it'll survive the shear.
remember 90L has an anticyclone over it right now, shear does not affect it.
Quoting TampaSpin:


At the end in the GOM my best guess that would appear to be at least a CAT3 maybe a 4 then oh no...five.


Thank you! Can I say "CRAP!"
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Quoting kmanislander:
There have been so many hurricanes over the years that anyone can find a track that matches their current thinking.
i know.seeing everyone post an old track is pointless and annoying.these storms go where they want.for every track there are 20 that are close to the same and hundreds that will put the storm in a completely different place.a 14 day forecast is like throwing the dice
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Quoting audioslave8:
90L doesn't look too good right now. Shear is hitting it - the same shear that ripped TD 2 apart. The center is east of the convection. And that convection is still rather weak. I don't think it'll be classified as a TD today unless some major changes occur during the day. And I'm starting to wonder if it'll survive the shear.


Well, you'd be wrong. There is an anti-cyclone over 90L deflecting it from shear. Dean had a similar look and it was classified. GFS has shear at 14 knots, but goes down to around 4-5 knots because of the Anti-cyclone. Besides the NHC says 'conditions are favorable for development' didn't say anything about 'unfavorable upper level winds'.
Member Since: August 10, 2009 Posts: 3 Comments: 672
Quoting TheCaneWhisperer:


Not liking that 5 day position the models are in agreement on. That's a double red flag for us, PBC here as well.
me either, now the biggest problem for us people that live in Florida is where it will make the curve, if it makes it early we are safe, it it makes it late then by the time it curves it will already be out in the gulf and that is a problem.
Quoting mikatnight:
Guess who.


Ahhh Andrew...I remember it soooooooo well!
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Quoting mikatnight:
Guess who.



Oh uh.. uhh.. Ike!? jking.
Andrew was a horrible storm, I wasn't around for it but I am sure thankful I wasn't.
Member Since: August 10, 2009 Posts: 3 Comments: 672
Quoting flsky:

Please explain why you're showing us these maps - I don't see the significance. Thanks.


Because its weather related.
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Chuck! Can you please put a stop to this rain for the weekend?!?!?!
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90L doesn't look too good right now. Shear is hitting it - the same shear that ripped TD 2 apart. The center is east of the convection. And that convection is still rather weak. I don't think it'll be classified as a TD today unless some major changes occur during the day. And I'm starting to wonder if it'll survive the shear.
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Quoting Stormchaser2007:


That would be a direct hit on me.


Not liking that 5 day position the models are in agreement on. That's a double red flag for us, PBC here as well.
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Out for now
Member Since: August 19, 2006 Posts: 0 Comments: 15948
3488. java162
Quoting mikatnight:
Guess who.



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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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