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TD 2 nearly dead; African disturbance 90L gathering strength

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

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

Hurricane

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

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.
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 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.


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

Have a great Friday everyone.
See ya later.
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.
3509. WxLogic
Quoting KEEPEROFTHEGATE:


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


That's for sure.
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!
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!
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
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!
90L looks very well organized on Visible this morning I would not be surprise if it is declared a TD3 by noon.
3516. LBAR
It's amazing what a couple of degrees of latitude (and longitude) can do for a tropical system!
How far does the dry air extend in front of 02? I can't find a satelite showing it far enough.
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.
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?
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.
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... :-)
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
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.
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....
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
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.
Good Morning Everybody!

Another August day in the tropics...
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.
Quoting canesrule1:
yup, models are saying Category 3 or higher before it reaches the northern Antilles, yikes!

Crap
3530. WxLogic
Quoting OSUWXGUY:
Good Morning Everybody!

Another August day in the tropics...


Morning...
we have a new map of tex tropical d two with more t.storm now cloud top over -60F
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
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.
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
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.
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.
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


Quoting canesrule1:
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.


Surely not time to run for the hills but, this weekend would be a good time to double check your preparedness and make sure the generator is operable ect....
Quoting chevycanes:

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.
true, but maybe it could be one if those spontaneous advisories the NHC gives, and unless a renumber happens very close to now we will have no TD at 11.
We cannot let our guard down never. Always prepare for the worst and wish for the best. If 90L fizzles good, but the models predict something different and the consensus is scary, It looks sorta like Georges to me and the GOM is boiling just too much heat accumulated and no significatnt storm this year to cool it down something gotta give....
red colors on ex tropical d two wow.. -60F CLOUD TOPS.
Quoting chevycanes:

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.


Yes, usually, but they can issue advisories before. They issued the first TD2 advisory - if I'm remembering correctly - at 6am ET. Which is for neither the formal or the intermediate.

I've not seen any renumbering yet, and the circulation still isn't tight enough. Dvorak isn't yet strong enough, either. I'd be surprised if it's upgraded before tonight (unless things change rapidly) but tomorrow may be a surer bet.
Both satellite estimates were T1.5 for 90L so its getting close.
3544. WxLogic
Quoting nrtiwlnvragn:
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




Sweet!!! G-IV mission to sample the area close to the Leeward Islands... that should help a lot defining upcoming forecast models specially for the 00Z runs onward.
Lets hope for High shear cause SSTS are high already.
Quoting jasoniscoolman10:
red colors on ex tropical d two wow.. -60F CLOUD TOPS.


Red is -70 buddy
One other thing that was not helping old TD2 was it was over cooler waters.....it has now entered waters that are 2deg Celicus WARMER than it has been in before......big time difference....
Quoting presslord:
there is a great deal of 'straight up and accurate' information on this site...but if you're depending on the Comments section of a blog for that then you deserve whatever misfortune befalls you...


Press, I saw this last night. Maybe my favorite comment ever. kudos.
Quoting TheCaneWhisperer:


Surely not time to run for the hills but, this weekend would be a good time to double check your preparedness and make sure the generator is operable ect....
yes very true, I remember Katrina when it passed here as a weak cat 1 and al the trees in Coral Gables were down power was out for 5 days and there was roof damage, and I also remember seeing a large truck full of stolen generators several streets from where i live.
Quoting TampaSpin:


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....


I'm not seeing any of the hallmark arc clouds typically produced when battling dry air??
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?
Quoting canesrule1:
lol, yes all models are taking it though the Hebert Box as a major hurricane, so SFLA must watch this very carefully.


Hehe, I'm an accountant so I don't know what an anti-cyclone, an MJO, or a SAL (note the sarcasm) is, but ask me anything about stats (Hebert Box) and you're going down!
Why are we saying that it's going to hit SFLA as a major and it hasn't even past 35 degrees west?
Quoting BatTracker:


Hehe, I'm an accountant so I don't know what an anti-cyclone, an MJO, or a SAL (note the sarcasm) is, but ask me anything about stats (Hebert Box) and you're going down!
lmao.
Quoting weatherwatcher12:
Why are we saying that it's going to hit SFLA as a major and it hasn't even past 35 degrees west?
have you not seen the long range models? they have been very consistent with it very close to SFLA.
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.


Hey Storm-

I'm not sure about the adjustment in lapse rate schema you describe...

If dry air is entrained in the low levels, it lowers the the equivalent potential temperature of the air parcels - which quickly lowers CAPE and would weaken updrafts.

If dry air is entrained in the sides of a warm, moist updraft at the mid levels it cools the updraft/lowers its Theta-E making it more stable than it otherwise would be.

In order to change the lapse rates, you need to change the Ambient evironment, not the environment within the low/mid level circulation. Really you need cooler air moving in aloft, or higher Theta-E air moving it at the lower levels.

Within the tropical environment, you typically have a "trade wind inversion", but I can't figure out a situation where dryer air would help weaken this inversion.

Quoting BatTracker:


Hehe, I'm an accountant so I don't know what an anti-cyclone, an MJO, or a SAL (note the sarcasm) is, but ask me anything about stats (Hebert Box) and you're going down!

Based on current forcast models, Herbet Box 1... for sure.. http://www.hurricanecity.com/hebertbox.htm
StormW,at this point and I stress at this point it looks as though 90L will end up in the gulf...Am I reading this correct. And I know things can and will change but that is they way it looks at this point in time correct?
Quoting canesrule1:
have you not seen the long range models? they have been very consistent with it very close to SFLA.

So, those can change very quickly. I have seen that for my self.
Nobody can say that with certainty, but prepare for the worst and wish for the best...
Advantage 90L

Quoting RescueAFR:

Based on current forcast models, Herbet Box 1... for sure.. http://www.hurricanecity.com/hebertbox.htm
yup, which means SFLA is in big danger because most models have it as a CAT 3 or higher by the time it passes the Hebert Box.
Quoting TheCaneWhisperer:


I'm not seeing any of the hallmark arc clouds typically produced when battling dry air??


The dry air is really acting to keep the convection from expanding.
I'm really surprised at the remarkable grouping of the forecast models this morning.
Quoting weatherwatcher12:

So, those can change very quickly. I have seen that for my self.
i know i have seen them too, but they have been consistent with 90L being close to SFLA for the past 72 hours+.
Quoting Elena85Vet:
Advantage 90L

Stupid remnant low, tell her no one wants her and she could die already! sheesh, lol.
Nonsensical blog tidbit of the day -

There were 25,350 posts in June
32,237 posts in July
and 27,231 posts so far in Aug.(approx)

For a total of 84,818 posts since the start of hurricane season.

All of that and not 1 name yet - LOL!!

Going to get that first name shortly, unfortunately. Keep up the good work everybody!!
Quoting canesrule1:
Stupid remnant low, tell her no one wants her and she could die already! sheesh, lol.


I've been trying to call her all morning to her cell phone, but either she is in a dead zone ar she wount speak to me I'll keep on trying...
Quoting claimsadjuster:
StormW,at this point and I stress at this point it looks as though 90L will end up in the gulf...Am I reading this correct. And I know things can and will change but that is they way it looks at this point in time correct?


I wouldn't say with any degree of certainty that it will end up in the gulf - at this point looks like the gulf up to outer banks needs to keep an eye out:



Quoting CaneHunter031472:


I've been trying to call her all morning to her cell phone, but either she is in a dead zone ar she wount speak to me I'll keep on trying...

Nice helo...SH3?
PErsonally, I think the remnant of 02L is likely a TD again...they shouldn't have discontinued advisories so quickly...
Quoting WxLogic:


Morning...


Morning to you WxLogic.

3575. jipmg
Quoting canesrule1:
Stupid remnant low, tell her no one wants her and she could die already! sheesh, lol.


whats wrong with the remnant low, ever since yesterday it was like you had a grudge against it LOL
Quoting weatherboykris:
PErsonally, I think the remnant of 02L is likely a TD again...they shouldn't have discontinued advisories so quickly...


While they could have continued, I believe it was the right decision considering even the satellite estimates are still T1.0 which is below TD strength.
3578. Greyelf
NEW BLOG.
Quoting canesrule1:
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.


I dont know where you are getting a catagory 4 storm coming to SFLA. Now im not down casting but it is likely that 90L will interact with land, and hopefully some tall mountains before it comes in SFLA's "General" direction.

Now keep in mind this is 10-13 days away so anything can happen. When they send a plane in there to gather data in and around 90L, we may see a major model shift. So just be prepared for anything mother nature may throw at you.
I just come from the GOM spent two days there doing sea trials with the USCG. Heat content is so high you can feel the steam comming out and caused problem for us cooling water and other issues. If 90L comes to the GOM and shear is low the Gulf Coast will get a big one, believe me. The ev\nvironment in the GOM is very conducive of a major storm as far as SSTs is concerned, so all we can hope for is for high shear and perhaps we should concentrate on shear forecast for that region, because the models prediction is not good so far...
Quoting TaminFLA:


I also live in Okeechobee. The right storm comes through and we could have ourselves another Katrinia. The dyke is in horrible condition!

Wow, a few people in okeechobee, I am here at the moment also, I go back and forth to key west,
NEW BLOG.
Really dumb question but here goes...

Crowne Weather says, "The forecast guidance is still forecasting that a trough of low pressure will be in place over the eastern United States in the day 6 to 10 time period, so Invest 90L/Ana may be pulled northwestward towards the United States. Therefore, this system has the potential to threaten the eastern Gulf of Mexico, Florida and the East Coast."

1)If there is a trough of low pressure over the East Coast, why does the East coast have to monitor..other than the possiblity that anything can happen.

2)Is Mississippi Eastern Gulf Coast or more Central??

I know these are weird questions but I am lurker....a concerned yet confused lurker!

Thanks all...keep up the good work.
Quoting StormW:


Again, the GOMEX scenario is one possibility. I want to point out...folks living on the Gulf coast shouldn't get uptight right now. We have time to watch this. A decent way to have a good idea about a GOMEX event will be to use the Lesser Antilles as a benchmark, as the system approaches. However, folks should take this quiet time to ensure they are prepared.


This is a very professional and responsible advise. Just go thru your list of things you need to have in the event that a major hurricane heads to your area, but do not panic yet there is plenty of time ... Prepare for the worst and wish for the best....
THIS EX TROPICAL D 2 ...WOW.. I THINK WE NEED TO WATCH THIS STORM AGAIN.