Tropical storm Debby

[kold weather]

The 4th depression of the Atlantic season has just formed from invest 96L, or the large wave that was off Africa heading close to the cape verde islands. Looks pretty impressive and could well be our next tropical storm soon. Key has been the reduction of convection in the northern half thanks to SAL which has exposed a clear LLC which is just in the southern mass of convection.

My previous discussion still stands, the only difference is that my ideas that its a TD are confirmed:

Convection has waned over the last few hours in reponse to a strong SAL outbreak once more coming out of Africa to its north which has weakened the northern quadrant on the system and has meant that it has becoming slightly lop-sided to its southern side which is in the more favorable air however the SAL to its north should not stop this becoming a tropical depression unless the system actually heads further north with the SAL still there and unjests a big dose of it into the ciruclation which it isn't doing just yet despite the weakening of the convection on the northern side.

NATIONAL HURRICANE CENTER NORTH ATLANTIC OBJECTIVE AIDS FOR

TROPICAL DEPRESSION FOUR (AL042006) ON 20060821 1800 UTC

...00 HRS... ...12 HRS... ...24 HRS... ...36 HRS...

060821 1800 060822 0600 060822 1800 060823 0600

LAT LON LAT LON LAT LON LAT LON

BAMD 12.3N 21.0W 13.4N 23.2W 14.7N 25.2W 16.4N 27.4W

BAMM 12.3N 21.0W 13.6N 23.1W 15.3N 25.3W 17.3N 27.6W

A98E 12.3N 21.0W 12.9N 23.1W 13.6N 25.4W 14.7N 27.8W

LBAR 12.3N 21.0W 13.1N 23.3W 14.4N 25.7W 15.7N 28.0W

SHIP 30KTS 37KTS 44KTS 49KTS

DSHP 30KTS 37KTS 44KTS 49KTS

...48 HRS... ...72 HRS... ...96 HRS... ..120 HRS...

060823 1800 060824 1800 060825 1800 060826 1800

LAT LON LAT LON LAT LON LAT LON

BAMD 18.3N 29.7W 22.1N 34.3W 25.3N 38.5W 28.0N 42.4W

BAMM 19.5N 30.1W 23.3N 35.2W 26.6N 40.2W 29.9N 44.3W

A98E 16.4N 30.3W 19.0N 36.0W 22.3N 41.7W 26.7N 46.2W

LBAR 17.0N 30.5W 19.5N 35.4W 22.1N 40.0W 24.8N 43.9W

SHIP 54KTS 59KTS 58KTS 53KTS

DSHP 54KTS 59KTS 58KTS 53KTS

...INITIAL CONDITIONS...

LATCUR = 12.3N LONCUR = 21.0W DIRCUR = 285DEG SPDCUR = 10KT

LATM12 = 11.9N LONM12 = 19.0W DIRM12 = 285DEG SPDM12 = 10KT

LATM24 = 11.3N LONM24 = 16.7W

WNDCUR = 30KT RMAXWD = 60NM WNDM12 = 25KT

CENPRS = 1007MB OUTPRS = 1013MB OUTRAD = 225NM SDEPTH = D

RD34NE = 0NM RD34SE = 0NM RD34SW = 0NM RD34NW = 0NM

By the way, this one could well be a threat to the cape verde islands, could well hit as a tropical storm. Beyond that little risk to the US as it should re-curve.

Edited August 21, 2006 by kold weather

[summer blizzard]

http://www.nrlmry.navy.mil/htdocs_dyn/tc_p...-210W.100pc.jpg

Tropical Depression 4 in all its glory although it looks more like a Tropical Storm to me.

[Gray-Wolf]

Well that seemed a long time coming! The RAMSDIS visual loop (1KM res) shows its rotation quite well too.

thanks to RAMSDIS Online

Edited August 21, 2006 by Gray-Wolf

[kold weather]

SB-Yeah it certainly looks like a tropical storm to me as well, really very impressive structure at the moment, up there with some of the better looking TD's and it wouldn't at all suprise me to wake up to TS Debbie providing it doesn't injest too much in the way of dry air via its northern inflow channel. Looks good though and no shear threat right now, the only real problem for now I can foresee is dry air but its holding up against that threat quite well and I can see some decent strengthening between 24-72hrs out as it moves away from Africa and the constant dry air ingestion.

First discussion from the NHC, takes it upto 60kts, just short of hurricane status and along the same sort of lines as the SHIPS model ideas:

Tropical Depression Four Discussion Number 1

Statement as of 5:00 PM EDT on August 21, 2006

the area of low pressure southeast of the Cape Verde Islands has

been maintaining enough convective banding today to warrant Dvorak

classifications of t1.5 from TAFB and SAB at 18z. Since then...a

small burst of convection has developed near the circulation

center. Given this...and the broad cyclonic envelope of the

low...advisories are initiated on Tropical Depression Four.

The initial motion is 285/10. The depression is south of the

subtropical ridge...but this ridge is forecast by global models to

slide eastward as a series of mid-latitude short waves move through

the central Atlantic and erode the ridge. This should allow the

depression to take a track between west-northwest and northwest

around the periphery of the ridge throughout much of the forecast

period. The official forecast is in good agreement with the GFS

and GFDL guidance...as well as the BAM suite of models. Neither

the UKMET nor NOGAPS hang on to the cyclone and these models take

its remnants westward.

Outer banding structures are well defined...but overall the

convective signature is still a little thin. Water temperatures

should be warm enough for the next day or so to support development

and the shear is light. During days 2 and 3 of the forecast period

the cyclone will be moving over somewhat cooler waters and the

official forecast shows only slow development after that. The

intensity forecast is close to a blend of the SHIPS and GFDL

guidance.

Portions of the Cape Verde Islands are within the forecast tropical

storm force wind swath...and the government of the Cape Verde

Islands has issued a Tropical Storm Warning.

Forecast positions and Max winds

initial 21/2100z 12.5n 21.5w 30 kt

12hr VT 22/0600z 13.0n 23.0w 35 kt

24hr VT 22/1800z 14.2n 25.2w 45 kt

36hr VT 23/0600z 15.5n 27.5w 50 kt

48hr VT 23/1800z 17.0n 30.0w 55 kt

72hr VT 24/1800z 20.0n 35.5w 55 kt

96hr VT 25/1800z 23.5n 41.0w 60 kt

120hr VT 26/1800z 26.5n 46.5w 60 kt

$$

forecaster Franklin

Edited August 21, 2006 by kold weather

[crimsone]

A Cape Verde storm in the making? I guess time will tell. It's certainly taken long enough to see it! lol

[Gray-Wolf]

Soon be having the "isn't that an eye?" posts.............. (but isn't th.........)

Thanks again RAMSDIS Online

Edited August 21, 2006 by Gray-Wolf

[crimsone]

:lol:

[wolves78]

Soon be having the "isn't that an eye?" posts

lol lets see how long the eye spy game will last

[summer blizzard]

Just thought that i would give my thoughts on this system, currently, the only thing standing in its way is Saharan Dust as it should be in a light shar environment for the next few days, steering currents are also fairly weak, so we should see a mostly west-north westward movement and gradual development.

The current position of the system is 12N 22W with a strength of 35mph.

Here are my thoughts...

24 hours - 12N 26W with a strength of 50mph

48 hours - 12N 30W with a strength of 60mph

72 hours - 14N 34W with a strength of 70mph

96 hours - 16N 40W with a strength of 80mph

120 hours - 16N 46W with a strength of 90mph

144 hours - 16N 52W with a strength of 100mph

[SMU]

http://radio.nhcwx.com/flghchp/displayimag...um=2&pos=86

S

[Gray-Wolf]

http://radio.nhcwx.com/flghchp/displayimag...um=2&pos=86

Thanks for that! cuts out a lot of legwork and gives you plenty of pointers.

S

[parmenides3]

Love that, Steve, thanks. Isn't the accent great, too?

One for KW, here, who spotted this first.

P

[Kain]

Wow didnt realise they could form that far east of the US waters..

Kain

[crimsone]

NHC Forecast discussion 2...

000

WTNT44 KNHC 220221

TCDAT4

TROPICAL DEPRESSION FOUR DISCUSSION NUMBER 2

NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL042006

1100 PM EDT MON AUG 21 2006

TROPICAL DEPRESSION FOUR REMAINS A LARGE AND WELL-ORGANIZED

SYSTEM...DESPITE A DECREASE IN THE INNER CORE CONVECTION. A

21/1914Z QUIKSCAT OVERPASS INDICATED THE DEPRESSION HAD A SURFACE

WIND FIELD ENVELOPE AT LEAST 500 NMI IN DIAMETER...WITH NUMEROUS

25-30 KT UNCONTAMINATED WIND VECTORS LOCATED IN THE DRY SLOTS.

BASED ON THIS INFORMATION...AND THE LACK OF INNER CORE CONVECTION

...THE INITIAL INTENSITY IS BEING MAINTAINED AT 30 KT.

THE INITIAL MOTION ESTIMATE IS 285/13...BASED ON A 10-HOUR AVERAGE

MOTION USING PASSIVE AND QUIKSCAT MICROWAVE SATELLITE DATA. THE

AFOREMENTIONED QUIKSCAT OVERPASS INDICATED THE CENTER OF TD-4 WAS

SOUTH OF 12N LATITUDE AT THAT TIME...PROBABLY DUE TO REFORMATION OF

THE BROAD LOW-LEVEL CENTER CLOSER TO THE BAND OF DEEP CONVECTION IN

THE SOUTHERN SEMICIRCLE. THE GLOBAL MODELS...AS WELL AS THE GFDL

AND THE BAM MODELS...REMAIN TIGHTLY CLUSTERED AND IN EXCELLENT

AGREEMENT ON AN IMMEDIATE NORTHWESTWARD MOTION. UNFORTUNATELY...

THE MODELS HAVE ALSO BEEN EXCELLENTLY WRONG THUS FAR. TD-4 IS

CURRENTLY AT LEAST 60 NMI SOUTHWEST OF THE 18Z GFS FORECAST

POSITION FOR 22/00Z...AND THE OTHER MODELS ARE SIMILARLY TOO FAR TO

THE NORTHEAST OF THE CURRENT POSITION. AS A RESULT...I AM NOT TOO

ENTHRALLED WITH THE MODEL SOLUTIONS...AND WE MAY SEE THE CYCLONE

TURN OUT TO BE MORE OF A WEST-RUNNER THAN A RECURVER THROUGH THE

STRONG SUBTROPICAL RIDGE LOCATED TO THE NORTH. WATER VAPOR IMAGERY

AS WELL AS WATER VAPOR-DERIVED WINDS AND UPPER-AIR DATA FROM THE

CAPE VERDE ISLANDS SUGGEST THAT THE MID-LEVEL EASTERLY FLOW ON THE

SOUTH SIDE OF THE RIDGE IS STRONGER THAN THE MODELS HAVE BEEN

FORECASTING...AND THE RIDGE TO THE NORTH ALSO APPEARS TO BE

BUILDING WESTWARD. THE FORECAST TRACK WAS SHIFTED TO THE WEST OF

THE PREVIOUS ADVISORY...BUT NOT AS FAR WEST AS THE CLIPER MODEL AND

STATISTICAL-DYNAMICAL MODELS OUT OF RESPECT FOR THE SKILL OF THE

GLOBAL MODELS. HOWEVER...IF TD-4 DOES NOT MAKE IT AS FAR NORTH AS

20N LATITUDE WITHIN 4 DAYS...THEN THE CYCLONE WILL LIKELY MISS THE

WEAKNESS IN THE RIDGE THAT ALL THE MODELS FORECAST TO DEVELOP.

THE INTENSITY FORECAST WAS LOWERED SLIGHTLY IN THE FIRST 48 HOURS

DUE TO THE LACK OF INNER-CORE CONVECTION AND WEAK TO MODERATE

UPPER-LEVEL NORTHEASTERLY SHEAR FORECAST TO UNDERCUT THE OTHERWISE

IMPRESSIVE AND EXPANDING OUTFLOW PATTERN. AFTER THAT...GRADUAL

STRENGTHENING IS EXPECTED AS THE SHEAR DECREASES TO 5-10 KT AND THE

CYCLONE IS FORECAST TO BE OVER WARMER WATERS.

DUE TO THE LARGE WIND FIELD DEPICTED IN THE EARLIER QUIKSCAT

OVERPASS...12-FT SEA HEIGHT RADII WERE ADDED TO THE FORECAST.

FORECAST POSITIONS AND MAX WINDS

INITIAL 22/0300Z 12.2N 23.2W 30 KT

12HR VT 22/1200Z 12.9N 25.1W 35 KT

24HR VT 23/0000Z 14.1N 27.7W 40 KT

36HR VT 23/1200Z 15.9N 30.6W 45 KT

48HR VT 24/0000Z 17.5N 33.4W 50 KT

72HR VT 25/0000Z 20.5N 38.4W 60 KT

96HR VT 26/0000Z 24.0N 44.5W 65 KT

120HR VT 27/0000Z 27.0N 51.0W 65 KT

$$

FORECASTER STEWART

Edit: Just to update with the info from the models and advisory 2A...

REPEATING THE 200 AM AST POSITION...12.5 N...24.0 W. MOVEMENT

TOWARD...WEST-NORTHWEST NEAR 16 MPH. MAXIMUM SUSTAINED WINDS...35

MPH. MINIMUM CENTRAL PRESSURE...1007 MB.

THE NEXT ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE CENTER

AT 500 AM AST.

4ch Met8 IR loop - http://www.ssd.noaa.gov/PS/TROP/DATA/RT/eatl-ir4-loop.html

Seems from the NHC Advisory that TS Debbie is immanent,...

One question - just what does a naming ceremony for a tropical storm involve? Is there wine and chocolate?

Edited August 22, 2006 by crimsone

[Gray-Wolf]

" as a result... I'm not to enthralled by the model solutions......." good old N.O.A.A., always there with sound advice/observations. There looks to be another biggy about to roll off Africa behind TD4 as well!

[crimsone]

This bit was my own personal favorite part of that advisory...

"The Global models, as well as the GFDL and the BAM models remain tightly clustered and in excellent agreement on an immediate northwestward motion. Unfortunately, the models have also been excellently wrong thus far."

That does look like another big wave on the african mainland, but I wasn't sure if perhaps it was part of a quasi-barotropic (that's a new word for me! lol) system over africa at the moment? (unlikely I know! lol)

Well, at least this year can't possibly be as quiet as the year I was born in (1982)... http://www.skeetobiteweather.com/history.asp

Edit: My word! 1983 was even quieter!

Edited August 22, 2006 by crimsone

[kold weather]

I'm very impressed with Td4 this morning given the amoun tof SAL that is still coming from Africa. Got a very good organisation at the moment and is I believe a 35kt tropical storm, though the lack of mconvection over the center at the time stopped it mfrom being upgraded, should probably be upgraded soon given the increase in convection and also the sat estimates have increased in response t othe central burst of convection.

As for track I note that Mr. Stewart thinks this storm will get further west then expected and I'm inclined to agree. Though it'll still re-curve before the USA it could end up getting quite close to Bermuda. The problem is the models have a habit of wakneing ridges too fast. We see it all the time here with the models being over-prgoressive in weakneing highs only for their ideas to prove to fast. The same is probably going to happen here and the re-curve area will probably be pushed further and further west.

As for strength, well for now it shouldn't get too strong that fast at least in the next 24hrs, the dust and dry air from Africa should limit its northern section and make getting beyond 45mp hard to do. However by tommorow africa should only really be on the far eastern section of its inflow and the amount of moisture its absorbing into that northern quadrant should increase which should mean some strengthening towards hurricane strength is possible though much above 80-90mph would be hard given the SST's in the area its moving into isn't that impressive at least for the next 120hrs...however I have said things like that before and been proven very wrong so I certainly won't rule out Td4 becoming quite a powerful system, esp as Karl moved into a similar area and become a strong cat-4 in 2004.

(ps, that wave over Africa is very impressive, could be our next depression IF the other areas don't get there first.)

[Somerset Squall]

This bit was my own personal favorite part of that advisory...

"The Global models, as well as the GFDL and the BAM models remain tightly clustered and in excellent agreement on an immediate northwestward motion. Unfortunately, the models have also been excellently wrong thus far."

That does look like another big wave on the african mainland, but I wasn't sure if perhaps it was part of a quasi-barotropic (that's a new word for me! lol) system over africa at the moment? (unlikely I know! lol)

Well, at least this year can't possibly be as quiet as the year I was born in (1982)... http://www.skeetobiteweather.com/history.asp

Edit: My word! 1983 was even quieter!

Check out 1914!

[summer blizzard]

000

WTNT34 KNHC 221453

TCPAT4

BULLETIN

TROPICAL DEPRESSION FOUR ADVISORY NUMBER 4

NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL042006

1100 AM AST TUE AUG 22 2006

...DEPRESSION BEGINS TO MOVE AWAY FROM THE CAPE VERDE ISLANDS...

AT 11 AM AST...1500 UTC...THE GOVERNMENT OF THE CAPE VERDE ISLANDS

HAS DISCONTINUED THE TROPICAL STORM WARNING FOR THE CAPE VERDE

ISLANDS.

AT 1100 AM AST...1500Z...THE CENTER OF TROPICAL DEPRESSION FOUR WAS

LOCATED NEAR LATITUDE 13.6 NORTH...LONGITUDE 26.1 WEST OR ABOUT 140

MILES...225 KM...SOUTHWEST OF THE SOUTHERNMOST CAPE VERDE ISLANDS.

THE DEPRESSION IS MOVING TOWARD THE WEST-NORTHWEST NEAR 17 MPH...AND

THIS GENERAL MOTION IS EXPECTED FOR THE NEXT 24 HOURS.

MAXIMUM SUSTAINED WINDS ARE NEAR 35 MPH...55 KM/HR...WITH HIGHER

GUSTS. SUSTAINED WINDS TO 35 MPH WERE REPORTED EARLIER THIS MORNING

ON THE ISLAND OF FOGO IN THE CAPE VERDE ISLANDS. THE DEPRESSION IS

EXPECTED TO BECOME A TROPICAL STORM DURING THE NEXT 24 HOURS.

ESTIMATED MINIMUM CENTRAL PRESSURE IS 1007 MB...29.74 INCHES.

ADDITIONAL RAINFALL ACCUMULATIONS OF 1 TO 3 INCHES ARE POSSIBLE IN

THE SOUTHERN CAPE VERDE ISLANDS.

REPEATING THE 1100 AM AST POSITION...13.6 N...26.1 W. MOVEMENT

TOWARD...WEST-NORTHWEST NEAR 17 MPH. MAXIMUM SUSTAINED WINDS...35

MPH. MINIMUM CENTRAL PRESSURE...1007 MB.

THE NEXT ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE CENTER AT

500 PM AST.

$$

FORECASTER FRANKLIN

FORECAST POSITIONS AND MAX WINDS

INITIAL 22/1500Z 13.6N 26.1W 30 KT

12HR VT 23/0000Z 14.6N 28.1W 35 KT

24HR VT 23/1200Z 16.1N 30.7W 40 KT

36HR VT 24/0000Z 17.6N 33.4W 45 KT

48HR VT 24/1200Z 19.2N 36.3W 50 KT

72HR VT 25/1200Z 22.0N 42.5W 60 KT

96HR VT 26/1200Z 25.0N 48.0W 65 KT

120HR VT 27/1200Z 28.0N 53.0W 65 KT

$$

FORECASTER FRANKLIN

[kold weather]

This really should be upgraded soon to a tropical storm. The depression has seen another slight convective burst that has re-covered the center after convection breifly waned this afternoon as is per normal for depressions at this stage of the game. Still the cloud tops are cooling somewhat now and has increase din coverage. Obvious banding, the best this year and even more impressive then the thre eother sheared TS we've had this season. It is clearly to my mind a tropical storm and thus should be upgraded as such very soon even if the convection is a little shallow for such a system (Its under marginal SST's so convection isn't going to be that deep yet.) Coupled to this the Sat estimates all have this as a 35kts tropical storm. Given all this agreement plus the very impressive structure and the re-emerganc eof convection it wil lbe upgraded next advisory as the only reason it wasn't last time was the wane in convection which has now been corrected by the system.

Track is slowly being pushed further west as the models delay the weakening in the ridge however re-curve stil by far the most likely option of all the options up for offer. In term sof strength, well there isn't much in the next 24-36hrs that should wekane it bar the annual flare-downs that occur from time to time howe ver shear remains light and should remian light till at least 96hrs time when slightly strong shear may occur on the northern side of the system. However for noce dry air should be no problem as it has a large amount of moist air around it:

http://www.ssd.noaa.gov/goes/flt/t1/sloop-wv.html

So in general this should be quite a long lasting system to track and will serbe well to increase the ACe total for this season quite massivly (~As its been a touch low so far this season thanks to 3 short trakcing TS.) however there should be no landfall with the only true threat probably for Bermuda. The real threat for the USA however comes from 97L.

[Paranoid]

Just a question. By no landfall, do you mean this storm is going to curve away from the US or is it going to weaken before reaching the East coast?

I'm also surprised this isn't Tropical Storm Debbie yet. The GFDL model showed 37kts at flight level for the last advisory. I would've expected it to strengthen since then.

[crimsone]

It's likely to curve into the mid atlantic - out to sea but never the less roughly following a lin parralel to the US eastern seaboard.

[kold weather]

Yeah I don't think this depression is going to die like the other ones so far this year and I do think Td4 will be with us in some form for the next 7-10 days as well so its going to be a long tracker I dare say. The only things that can really cause problems now is the SAL and an intrusion in about 36hrs time as it moves into that region and also the southerly shear the SHIPS are forecasting to be impacting it by 96hrs.

Edited August 22, 2006 by kold weather

[crimsone]

I'd just hate to think what could potentially happen to a storm of this physical size if we'd ALL got it wrong and it managed to make it to the carribean or the gulf. It's very very unlikely, but never say never - we've all been playing guessing games and getting it wrong to a certain extent with the other three TC's so far this season - inclusive of all the models and the NHC themselves.

[crimsone]

Advisory 5...

REPEATING THE 500 PM AST POSITION...14.5 N...27.5 W. MOVEMENT

TOWARD...WEST-NORTHWEST NEAR 18 MPH. MAXIMUM SUSTAINED WINDS...35

MPH. MINIMUM CENTRAL PRESSURE...1005 MB.

Pressure dropped by 2mb, speed increased by 1mph, max winds pretty much unchanged.

It's either not doing much yet, or it's just starting to strengthen. I'm not going to place a monetary bet on either. lol