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TD 8? Not yet...

By: Dr. Jeff Masters, 4:05 PM GMT on July 29, 2005

Satellite imagery of the tropical wave approaching Puerto Rico shows a less impressive system than yesterday. The wave covers less area, has reduced upper level outflow, and is battling increased wind shear. However, the dry air on the wave's west side that was inhibiting thunderstorm development last night is less apparent on today's water vapor satellite imagery.

The most most impressive sign of organization of this wave is in the pressure falls observed over the Lesser Antilles islands this morning. A plot of the past week's pressures at one of our personal weather stations in Anguilla, an island in the northern Lesser Antilles about 150 miles east of Puerto Rico, shows a significant pressure fall this morning:

Keep in mind that it is a bit tricky to interpret pressure readings in the tropics. The pressure plot shows a curious regular oscillation with amplitude 1 mb, and a peak twice per day at about 11am and 11pm local time. This oscillation is due to the presence of atmospheric tides in the atmosphere. Like tides in the ocean, atmospheric tides move as a wave around the planet with a very regular period in sync with the Earth's rotation rate. The atmospheric tides we see in the Anguilla data are primarilly due to solar heating of the atmosphere. When the sun rises and starts heating the air, the air expands in response, lowering the pressure in the vicinity, and pushing a wave alternating high and low pressure air all the way around the globe. The amplitude of this wave is highest--about 1.5 mb--where the sun's heating is greatest, near the equator. The wave's minimum amplitude of about 0.5 mb occurs near the poles. The period of the wave is 12 hours.

Mentally remove the wriggles from the pressure plot above, and you can see that the drop in pressure this morning in Anguilla was not due just to the atmospheric tidal effect, but must also have had a component due to a low pressure system moving in. Similar pressure falls are being observed on nearby islands that the tropical wave is affecting, such as St. Maarten.

A hurricane hunter aircraft will investigate the area at 4pm today to see if a tropical depression is forming. If a depression does form, its potential track is highly uncertain. The GFS model maintains that it will track WNW and threaten the East Coast, while the ECMWF has the system moving into the Gulf of Mexico. The GFDL model moves the system into the Bahamas and disipates it in 36 hours. In any case, if a depression does form, it will have some significant barriers to overcome in order to intensify. If the storm moves north, there is a large upper-level trough with strong shearing winds to contend with. If the storm stays further south, interaction with the land masses of Puerto Rico and Hispanolia will hinder it.

Dr. Jeff Masters

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

Models on this page clearly show that their are some discrepancies about how long the low stays active and where it might go. very interesting none the less.

This morning there seemed to be no surface circulation based on limited surface reports.

From looks of it a depreddion will not form.
lol this is funny
I sure would like to hear from Stormtop where exactly is the center of circulation of the TD he says has already formed in the Puerto Rico/Islands area.
i told everyone the pressures were falling in the islands and there was a circulation at 17.5 and 63.5...but nooooooooooooooooooooo no one believed me..i told you i have been doing this for 30 years and i know what im talking about...i will change just like the hurricane service does i will say that..i will go out on a limb with a forecast but not at this time...later when its named the 8th TD OF THE SEASON...
From 12Z Tropical Weather Discusion......
"A strong tropical wave is along a line from 23n56w to a 1012 mb low pressure center near 17n60w to 10n61w near northeastern Venezuela. Widely scattered moderate to isolated strong showers and thunderstorms already are reaching sections of the eastern Caribbean Sea islands from Guadeloupe near 16n to 20n between 58w and 63w."
look at the san juan weather radar very impressive right now...everything moving sw...
i want to thank you guys for not mentioning that word in front of me...you know the one i hate...
Stormtop, don't move the goalposts to make yourself look better. You said several times today a TD had already formed, if not TS Harvey, and the NHC was just waiting til the plane gets there to name it. Everyone already knew there was a very broad rotation at the surface in the area. It has been there since the disturbace came off of Africa. An elongated, broad rotation with no defined center is NOT a tropical depression. You can have a weak low pressure area with a disorganized, broad rotation for a long time without any tropical cyclone ever forming.
lol hawk i love it when you try to defend yourself i think its cute lol
hawk the only reason they are not calling it a TD 8 is they are waiting for the recon plane to get down there..i will gurantee it will be a TD 8 when the plane gets down there ..it may even be harvey..the reports i see winds are already being gusting to 35 in the islands.......
How about sharing some of those reports with the 35mph gusts?
this could be the east coast one i was talking about..i made mention in my forecast there would be one to hit the east coast...i EMPHASIZE THIS it is to early to give a forecast on this one...does everyone hear me im not giving a forecast on this one yet...
fred all you have to do is check the islands weather report like i got the pressures i have the winds..its not sustained fred but its gusts in st martins and anguilla...
Stormtop, I'm not defending myself so much as I'm just debunking the garbage you keep throwing out as fact on this message board.
And I'm not dismissing the possibility the recon plane will find some more defined center of circulation later this afternoon. I'm just saying there isn't one now.
19. Jet2
I have a question Dr. Jeff Master what is this thing at 75w and about 23n http://www.goes.noaa.gov/browsh.html, because it seems to have formed some closed circulation at least on infarared sat.
well if you go back and read my post..i said the following:
1 the pressures were falling in the islands..true

2 the winds have picked up in the islands true

3 there is a surface circulation true

4 i said it would not be confirmed until the recon plane gets down there true

what did i say was garbage...dr masters confirmed the pressure falls which you guys didnt believe...

i will take comments..
plenty of tropical wave's have created "GUST" that's what squall lines do.What defines a depression is when this wave begains to bow,this bow is normally due to mid level low pressure its still unknown exactly why some of these "Bows" develop into depressions. But a depression would be the next formation stage in hurricane development. BUT..you have to have a closed surface low before the system can be called a depression..What we are seeing in this wave is the "Bow" and it has some mid level circulation and has some squalls but nothing I see indicates a closed circulation at the surface.
how do you know that hawk you took your plane and checked it out lol...you are hillarious..
We are clear you need to reread well what I said.
IT HAS BEEN CLASSIFIED AS A SURFACE LOW..to me that meands it has a closed circulation and probably will be a depression when the plane reaches it...could even find harvey...i wouldnt be surprised looking at the radar out of san juan..
well rocket my friend you are disputing what the nhc says..they say SURFACE LOW.......
27. K8e1
come on guys...don't change now...we all know that its VERY important for us to downplay this td if the models have it curving toward the east coast...and it's VERY important that we play it up if its heading into the GUlf...stay consistent so you dont confuse me lolololol
classified a surface low does not define a depression..that simple,a depression is defined as a CLOSED surface low..This WAVE has no CLOSED surface low:)..
did you and hawk steal a plane and check out the low thats how you know that...lol
outrocket is right.
you went with them hurr king arent you just 17......
Stormtop you are so blinded by your own opinion that you cant see the truth even if its right in front of you on the satellites.
If I may say something... the folks at the NHC maybe already know that a TD has formed, but dont want to release that info until they have proof from a recon plane. they dont want to scare anyone since most people try to dismiss storms and some are already scared from previous ones.

oh and by the way its 15 get it right.
stormtop uou seem to have taken a plane down there yourself!
mobilehurricane has a new one you need to see this.
you*** and i agree with whirlwind the nhc probably like to be certain because there is no big need to rush at this point
with no agenda or bias (lol), it does seem that the northern part of the wave has gotten its act together. this morning it was pretty ragged, but more recently it has shown some bursting convection and closed circulation properties.
Even if it does form into something, its no big deal. Doesnt have enough time to strenghen. Just a rain maker, I hope it comes for the east coast of fl...yay
Ok, Stormtop, I'll agree with you that some kind of more defined center may be trying to form under the new cluster of convection south of St. Croix, just west(due to westward movement) of the lat/lon point you mentioned a little while ago. If that convection can maintain itself that may be the beginning of real organization.
something might be trying to form at 19n 62w .
Stormtop, you are going to be laughing at a lot of people on here besides me over the next few months if strongly disagreeing with you is a laughable offense.

I need to question one minor thing you said a bit ago... "dr masters confirmed the pressure falls which you guys didnt believe..."

I certainly don't remember anyone, including me, questioning any pressure falls. And as someone above said, a low pressure area and a closed circulation with a defined center are two different features.
RE: mobilehurricane's question about grounding the roof-mounted weather station:
Lightning rods are carefully designed to have sharp points allowing electrons in the earth that are attracted to the atmospheric positive charge to "jump" off the tip of the lightning rod. This lowers the electrical potential between the ground and the cloud, reducing the chance of lightning. Notice that well-installed lightning rod systems have many small points, not one large rod, because many small points will disperse more charge. Of course, if the charge can't be dispersed fast enough, the lightning will strike the lightning rod system instead of, say, your chimney because of the excellent ground .
So, the lightning rod first "repels" lightning by dispersing the charge but, if unsuccessful, "attracts" the direct hit.

Will grounding the weather station INCREASE the chances of a hit? My guess is that dry wood roof rafters are such poor conductors that lightning will have no interest in the weather station because electrons can't make it from the ground thru the rafters. However, it is certainly possible that the asphalt shingles connected to the roof connected to the walls connected to the ground provides a large enough pathway that the low conductivity is overcome. I liked the suggestion of a rubber grommet separating the post from the roof!

My free advice, worth every penny, is DON'T ground the weather station and DO put properly installed lightning rods on the house. I'd appreciate any technical feedback y'all can offer!
when i said the pressures were falling some of you didnt believe me ...i dont know if you were one of themm..alec sure didnt..
Jet2 asked:

I have a question Dr. Jeff Masters what is this thing at 75w and about 23n http://www.goes.noaa.gov/browsh.html, because it seems to have formed some closed circulation at least on infarared sat.

That is a tropical wave that needs to be watched for development. It did have a small circulation yesterday, but I can't pick one out today. It is sandwiched between two cold upper level lows that you can see spinning on the water vapor loops. These upper lows should provide enough shear to prevent the wave from developing into a depression. One cold upper level low is over Andros Island/western Bahamas; that is probably the circulation you noted on the infrared satellite image. The wave itself has no circulation at present.

Jeff Masters
whirlwind i agree what you are sayiny..that is my feeling exactly...
hurr king i stand corrected 15..you can learn lots on this blog just be patient and keep your ears open..i have seen more things then you will see in your life time..i assure you i will help you learn in anyway i can..im sorry if i hurt your feelings..im sure rocket and hawk feel thew same way i do about teaching you..
Am I seeing things on the IR sat loop or is there a upper low just to the west of the "tropical depression/wave" that we are talking about? Anyone notice the blob of persistant precip over the central bahamas?
Here is a link to the 18Z Surface Analysis which shows a strong wave with surface winds to 25kts and min presures around 1012-1013mb but you can't confirm a closed circulation from the data. The recon should be there soon.


stormtop, the part that I and others did not believe this morning is that the tropical wave had formed a closed circulation. There was just no evidence this morning of any west wind at the surface to the south of any possible center. A sse wind in the northeastern islands and a ne wind in PR and the Virgin Islands is a start, but it isn't enough, and with all the mid and high cloud debris over the water it has been difficult if not impossible to tell what the surface wind over the northeast Caribbean is doing. We'll have to wait and see what the recon plane says about the area just south of St. Croix. It is showing more promise this afternoon.
If an organized center does form near St. Croix, the system will struggle for a while while it moves over Puerto Rico and Hispaniola.
Not to bring back the Andrew debate,(its over we'll just have to agree to disagree), but an analysis of donna seems to be lowering the windspeed at landfall. I am eager to see what other things come out of the adjustment of the databse.
come to my blog
You have a link to the Donna info, tx?
sure here it is
its not official but I'm sure will be used when it comes up.
so who thinks the wave over puerto rico will be a depression at 5 pm?
I dont.
i think it might be, the winds are strong enough and the circulation is visible on radar
same as yesterday I don't, but if it has a center and 25+ winds they might upgrade. Btw thanks turtle for the Kendra link. Only storm I know of that got "destormed"
What radar?
puerto rico radar from the NWS, use the long range radar
I think I see the center.
Got to go.
You ever wish you could just get rid of all the mid and high clouds on the visible satellite loop so you could tell if there is a well defined circulation? All that cloud debris is really annoying me right now.

I'm not sure if they'll call it a depression at 5pm. It is clearly a bit better organized than it was 6-12 hours ago, but it is still tough to tell if there is a closed center rather than just broad rotation.
just look at the radar, the center is clearly visible near St. Croix, it is weak but enough to classify if they want to
Satellite also shows the outflow to the north and northwest has improved in the last several hours.
it wont be classified till 8pm because recon wont reach it until then
ya outflow is improving and the shear is lessening to about 10 kt, not much really
There may be an organizing center just south of St. Croix, but it is still quite weak. St. Croix is reporting a 5mph wind from the ene and St. Thomas is reporting only a 15 mph wind from the east.
the winds associated with the storm are probably more squally rather than a true windfield
the spiral bands are starting to become more pronounced on radar
does'nt look very impressive on the radar...looks like a "center" is trying to form but its farther south than where I thought it would be. Some dry air in there it seems like. I don't think the storm will be classified today.
Franklin is finally over with, its just been declared extratropical
you are right turtle this has been a depression all morning in my opinion and getting better organized all day also in my opinion...i think they migh be surprised when the recon gets there and find harvey instead of TD 8.......again my opinion only...
stormtrop, it may be a depression but as you know, the nhc waits to see if a storm holds together to give it a name. plus recon has only found 30 mph winds.
I'm trying to get to 1000 comments in my blog. Please come talk there.
wow,sounds like a waste of time
hawk i have seen it mant times before a troical storm go over hispanolia and lose strength and then come out in the warm waters of the caribbean +90 degree temps and reintensify..it might inhabit it in the short term but down the road it looks good for harvey ...just my opinion...i have not given and official forecast yet except i know there is a tropical depression down there which hawk is right they wont say anything until the 8pm adv...
I got to do somrthing dont I.
dude u only got 7 comments, it might take a year
who is hawk?
I had 70 until it had a glitch. I've seen blogs go from 0 to 400 in an hour before.
stormtrop, if this went over hispanolia it will probably be dead in hours, itspractically nothing right now
i think the center looks to be at 17.5 n and 65.5 or 66.0 west..thats my estimated position....
fine dont help.
stormtrop, what do you think will happen with this storm?
i disagree with you turtle there is always a chance a new center could form and i seen this happen to many times...i seen one go over every major island in the caribbean and survive and come out in the gulf and hit cat 2 status in september...the water temps are a little cooler in that month...so dont tell me it cant happen...this one will have no shear to overcome..
there is plenty of shear but beyond that, the storm might miss hispanolia but, if it doesn't it will die unless it just clips hispanolia
turtle i will give my official forecast when the plane confirms there is a TD OR TS down there...
Stormtop, it is certainly possible this system will move wnw and just scrape Hispaniola and move onward toward the Bahamas. The NHC may consider this thing near depression now, but I don't see how it could be Harvey yet. The wind around it is very light. The Virgin Islands to the north of the center are reporting no higher than 15 mph while Nevis to the east is less than 10 mph.
so far the plane hasn't found a circulation, it probably will but, why not forecast now if your so certain its a depression?
Storm, you must be referring to Hurricane George that went over all the big islands and ultimately survived.
turtle you are just going to have to wait on my forecast...and hawk i think they are not supposed to be down there until 4pm anyway..am i correct on that?
yes i am hawk..
stormtrop, their flying in it right now, their up to 12 observation statements
stormtrop, why did u say u are hawk?
Who's going to chuckle if this stupid wave we're bickering over dissipates?
storm is hawk.
ok turtle we will see....i still say they will issue something around 8pm possibly at 5pm...we will see i didnt hear what you are saying are where you are getting that info lets see..
Just saw a report, they are down there now and have so far not found any closed surface low. This is not a depression much less a tropical storm. I think Stormtop is hoping beyond hope so his prediction of 3 more storms in July might come true. It won't.
check out my blog, i said everything in there
3 more? thats off
stormgirl hawktop
toyotaman, did you just see the weather channel to?
looking at the latest sat. loop, there is still no closed circulation with this. There is one to the northwest of this heading to the southwest, but it has very few clouds.
Turtle, yes I did.
i see a circulation, but i guess its hard to see from all of the shower activity around it, on radar though its clear
Pull up the NHC web site and check the satillite loops and you will see what I mean.
Are you referring to the showers se of St Croix?
already did, i see a circulation in the main shower area but, its weak
toyotaman you have a plane to ..you went there and checked it out and beat the recon plane down there..you are a riot lol..
Stormtop, not to change the subject but have you seen the latest visible sat south of the Ala/Fla line? There is a broad circulation. Any comments?
yes the showers near St.Croix but, you have to look around those to see that there is a circulation.
Look real close, nothing is moving south, east, or north. Its all moving either wnw or sw. That does not make a closed low. T-storms in my area almost always go in different direction.
Stormtop, you keep asking if every has a plane but you have already called it a tropical storm. How did your plane or boat for that matter do?
well that is the movement of the storm but, lets not argue, if it is this hard to see a circulation it must be weak if it exists
isobar, looks like the remnants of a mesoscale complex, not much to worry about unless it flares, which it probably won't
yes i have lots of comments on that i made it this morning..i am worried about it and its sitting over the gulf stream...i saw convection fire up over it earlier and then died down..but to answer your question yes you should not write it off isobar let me know if you see the convection increase...good call..
Data from an Air Force Reserve unit reconnaissance aircraft...
satellite images...surface observations...and San Juan Doppler
radar data indicate the low pressure area associated with a strong
tropical wave moving through the northern Leeward Islands has not
yet organized enough to be classified as a tropical depression.
However...conditions appear somewhat favorable for a tropical
depression to form later tonight or Saturday over the extreme
northeastern Caribbean Sea and in the vicinity of Puerto Rico and
surrounding islands. Another reconnaissance aircraft is scheduled
to investigate the system tomorrow. Squalls producing brief periods
of heavy rainfall and gusty winds to near tropical storm force...
especially over higher terrain...could occur over the northern
Leeward Islands...the Virgin Islands...and Puerto Rico tonight...
and over Puerto Rico and Hispaniola on Saturday. Interests near
this area should closely monitor the progress of this system.
ok, its close but not a depression.....any comments Stormtrop?
there is a low after all but, weak
Don't buy it, Stormtop, the NHC is involved in an effort to discredit you. Their recon plane actually did find TS Harvey, but they are intentionall keeping that info from you.
all it takes is one good flare of convection to classify this thing.maybe at the diurnal maximum.
you read my post turtle do i have to repeat myself..i said you wont hear anything until 8pm tonight in a special advisory..i believe you agreed if you scroll up you will see what im talking about.
lol@ hawk
stormtrop it is possible, maybe at 11pm. I say 11pm because they want to wait and make sure if anything happens that it is actually gonna hold. Speaking of that thunderstorm activity is increasing alot over the storm. Any comments?
ok hawk now the nhc know what time i want them to drop the bomb on everyone in here lol......this is to funny.
turtle, this system definitely needs a big blowup of deep convection over the center-to-be, and it needs the convection to maintain itself rather than quickly diminish like it has been doing up to this point
comment you made turtle was 8pm agreeing with me..if you have amnesia scroll up you will see what you said...lol
i agree
ok stormtrop, i didnt say it was impossible, just facts have forced me to change my opinion
People, I think your depression is forming southeast of Puerto Rico or just south of St. Croix...check out this loop.

lol ok turtle i dont change my opinion on waht i say..i said 8pm and this is not a conspiracy and im sticking to it i dont hedge 3 hours...what is the difference if its a td at 8pm it will be a td at 11pm...
In an old book from 1964, Atlantic Hurricanes by Dunn, they said you had to have a west wind of at least 10 mph for a circulation in the easterly trades to be a depression--but I don't know if such a definition is used anymore.
Unless there is a big blowup of convection over the would-be center in the next few hours it is highly unlikely this thing will be called a TD before tomorrow.
This system looks similar in organization to the system that spawned TS Gert. Judging from the satellite appearance over the past few hours.. it does appear that the storms are trying to get better organized.. and perhaps even that a convective band is trying to consolidate to the northeast of the weak low. If this trend continues it would actually not surprise me to see a depression form sometime later tonight.
I think the wind shear needs to die down a bit before this system can develop further. From looking at the satellite the past few hours, the shear appears to be lessening somewhat. As I stated above, I believe the "center" or low level circulation MAY be forming just south of St. Croix where it appears that thunderstorms could be forming around it. Call me crazy, but that's what I see.
ever feel like this was an improv and we are mearly waiting for godot?
Actually, in the trades the models seem to be right biased this month--I remember that when Emily was first a wave and a depression the models had it heading north of the Leeward Islands and Puerto Rico. Now, this wave is most active in the NE Caribbean instead of to the north of Puerto Rico like it seemed it would be a couple days ago. If anything is forming (a big if) I think it will go WNW into Hispanola and get shredded in the mountains--maybe something could form from it again afterwards--or maybe not.
Godot would be an awesome name for a hurricane!
No need to shout Storntop, I did reread your post and you guarenteed that it would be a depression and possibly a storm. Well its not either. You also said that there would be 3 named storms by the end of the month, right? Only 2 days left my friend.
Agree with you St. Simon about most of the action being in the Northeastern Caribbean. I'm not sure about it going over Hispaniola though. It certainly does have a good chance of hitting Hispaniola and getting shredded, but I see it bypassing Hispaniola a bit to the South.
Ok time to guess how many storms will be named in August. My totally unscientific guess is 4 storms, 3 hurricanes and 2 majors. Record for August is 7 storms in 1995, record for any month is 10 (!) September in 1933.
we will see toyota......you dont plkan on doing smething to the atmosphere do you?i dont trust you toyota...you have to be watched closely....lol
hurricane watcher,are basing direction on the idea that the bermuda high will re-establis it's self afte upper low clears bahama's..If so you may be right ,that could keep this wave farther south.

You said "i will gurantee it will be a TD 8 when the plane gets down there ..it may even be harvey"


You got it wrong. The data from the plane is back, and there's no tropical depression yet.

Will you admit that you are wrong?
151. WSI
The depression isn't there yet. Whoever predicted it would be there when the plane flew in was wrong.
I just hope that stormtop predicts a landfall on the GA coast so I know I'll be safe (jk)
I predict it will hit North Carolina.
But first Florida
"hawk this will be harvey today if not right this minute when the recon plane goes and checks it out...the clear center is at 17.5 63.5...if you cant see it you are only fooling yourself."

Stormtop, do you remeber saying this earlier this morning on the other blog? This means that you did predict it to be a named storm today. Quit changing your story.
In astonomy news, this is interesting Link
i'm sorry, but I find it very hard to believe that you have been studying hurricanes for the past 30 years. Me thinks that you are a teenager judging by your temperment.
Last message to Stormtop of course.
whats up.....fill me in on the lastest....i looked at the lastest satellite loops....dont see anything....
Hey stormtop....im still collecting predictions for the total season.....
Outrocket, that's exactly what I'm basing my forecast on.
162. Alec
hi everyone!
163. Alec
im in the new blog now.
New Blog?