Disturbance 90L close to tropical depression strength; TD 2 may rise again

By: Dr. Jeff Masters , 2:02 PM GMT on August 14, 2009

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A strong tropical wave (90L), with a large circulation and a moderate amount of heavy thunderstorm activity, is a few hundred miles southwest of the Cape Verdes Islands, off the coast of Africa. This morning's QuikSCAT pass shows that 90L has a large circulation, but this circulation is not yet well-formed, as it is elongated along an east-west axis. Satellite imagery from the European METEOSAT satellite show that the heavy thunderstorms associated with 90L are gradually becoming better organized, with some spiral banding evident on the south side of the storm. Satellite intensity estimates from NOAA already put 90L at tropical depression strength with 30 mph winds, but the storm does not yet have a well enough formed circulation to be classified as a depression. 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 was. However, there is some dry air from the SAL being sucked into the circulation of 90L, and this is retarding its development.

Wind shear is moderate, about 10 - 15 knots, but is forecast to fall to the low range, 5 - 10 knots, later today. Shear is then forecast to remain low for the next five days. Sea Surface Temperatures are about 28°C, and will remain in the 27 - 28°C range the next five days. The combination of low wind shear and sufficiently warm SSTs should allow 90L to develop into a tropical depression by Saturday, and potentially reach hurricane strength by Wednesday. Most of our reliable models strengthen 90L into a hurricane by Wednesday, when the storm is expected to be near the northern Lesser Antilles Islands. One important outlier is the ECMWF model, which has 90L passing to the north of the islands, and eventually recurving out to sea east of Bermuda. The ECMWF was by far the most reliable model for forecasting hurricane tracks last year. However, all of our models are pretty unreliable going out 5 days in advance for systems that have yet to reach tropical depression strength. Once 90L becomes a tropical depression and develops a well-formed circulation, the models will have a better handle on forecasting where it will go.


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

Tropical Depression Two may come back
Tropical Depression Two died yesterday, but may rise again. Satellite loops of the remnants of the storm show that heavy thunderstorms are again attempting a comeback near the axis of what is now a tropical wave. However, dry air continues to interfere with the development of the thunderstorm activity, and moderately high wind shear of 15 - 20 knots is also inhibiting the process. Wind shear over the remnants of TD 2 is expected to remain in the moderate range, 10 - 20 knots, over the next four days. Sea Surface Temperatures (SSTs) are 27°C, but will warm to 28°C two days from now. There is plenty of dry, stable air from the Saharan Air Layer (SAL) to the north and west that will continue to cause the storm problems. The relatively cool SSTs and dry air mean that any re-development of the storm will be slow to occur. NHC has given the system a medium (30 - 50% chance) of becoming a tropical depression again by Sunday morning. Only one reliable model, the NOGAPS, is predicting regeneration of TD 2. The NOAA Hurricane Hunters are flying research missions into the remnants of TD 2 today and Saturday.

I'll have an update Saturday morning, or earlier, if significant developments occur.

Jeff Masters

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Quoting nrtiwlnvragn:

Take out CLP5 (climatology), and you have an insanely tight spread of models, especially for something that hasn't been fully initialized yet.
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Quoting cg2916:

Guys, it's illegal to access that info. Only NOAA can use it for official purposes.


Where do you think all of the various websites get their information to construct model plots?
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1132. cg2916
Quoting Drakoen:
The XTRAP is current on the northern side of the model guidance
Quoting Orcasystems:
Ok, I am not an english major.. but I do find this update a bit confusing??

SHOWER AND THUNDERSTORM ACTIVITY ASSOCIATED A BROAD AREA OF LOW
PRESSURE CENTERED ABOUT 250 MILES WEST-SOUTHWEST OF THE SOUTHERN
CAPE VERDE ISLANDS HAS BECOME A LITTLE LESS ORGANIZED OVER THE PAST
SEVERAL HOURS. HOWEVER...CONDITIONS STILL APPEAR FAVORABLE FOR
FURTHER DEVELOPMENT OF THIS SYSTEM...AND A TROPICAL DEPRESSION
COULD FORM DURING THE NEXT DAY OR TWO
AS IT MOVES WESTWARD AT NEAR
15 MPH. THERE IS A HIGH CHANCE...GREATER THAN 50 PERCENT...OF THIS
SYSTEM BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.


It's saying that lately, it's been disorganizing a little bit, but it still has a pretty good chance.
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1131. Patrap
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So what used to be Tropical Depression 2 is no longer an invest? How could that be? The storm, as it stands right now, looks relatively healthy and should at least be declared an invest.
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Quoting Orcasystems:
Ok, I am not an english major.. but I do find this update a bit confusing??

SHOWER AND THUNDERSTORM ACTIVITY ASSOCIATED A BROAD AREA OF LOW
PRESSURE CENTERED ABOUT 250 MILES WEST-SOUTHWEST OF THE SOUTHERN
CAPE VERDE ISLANDS HAS BECOME A LITTLE LESS ORGANIZED OVER THE PAST
SEVERAL HOURS. HOWEVER...CONDITIONS STILL APPEAR FAVORABLE FOR
FURTHER DEVELOPMENT OF THIS SYSTEM...AND A TROPICAL DEPRESSION
COULD FORM DURING THE NEXT DAY OR TWO
AS IT MOVES WESTWARD AT NEAR
15 MPH. THERE IS A HIGH CHANCE...GREATER THAN 50 PERCENT...OF THIS
SYSTEM BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.



Just a slight flux in the organization. Not really much change really. Still a high chance for TD formation.
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1127. LBAR
Quoting KEHCharleston:
This is a link to a webcam at 17N 25″W - Mindelo Harbor, (North side of Sao Vincete, Cape Verde)
Too far NE of 90L (11.7N 29W) to be cloud coverage from our invest, I would think - but an interesting picture, none the less.



Nice link! I'd love to visit the Cape Verde Islands someday...in Winter!!
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1126. Drakoen
The XTRAP is current on the northern side of the model guidance
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1125. KEEPEROFTHEGATE (Mod)
UNCLAS//N03146//
WTNT01 KNGU 141900
MSGID/GENADMIN/NAVMARFCSTCEN NORFOLK VA//
SUBJ/TROPICAL CYCLONE FORMATION ALERT//
REF/A/RMG/NAVMARFCSTCEN NORFOLK VA/131900Z AUG 09//
AMPN/TROPICAL CYCLONE FORMATION ALERT (WTNT02 KNGU 131900)//
RMKS/1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN
100 NM EITHER SIDE OF A LINE FROM 12.0N 26.5W TO 12.0N 30.5W
WITHIN THE NEXT 24 HOURS. AVAILABLE DATA DOES NOT JUSTIFY
ISSUANCE OF NUMBERED TROPICAL CYCLONE WARNINGS AT THIS TIME.
2. WINDS IN THE AREA ARE ESTIMATED TO BE 20 TO 25 KNOTS.
SATELLITE IMAGERY AND A RECENT 0720 UTC QUICKSCAT PASS INDICATES A
LOW-LEVEL CYCLONIC CENTER ALONG THE WAVE AXIS NEAR 12.0N 26.5W.
THE SYSTEM IS MOVING WEST AT 8 TO 13 KNOTS.
3. SEA SURFACE TEMPERATURES RANGE FROM 28 TO 30 DEGREES CELSIUS
ACROSS THE TROPICAL ATLANTIC. UPPER LEVEL WINDS OVER THE
SYSTEM ARE EASTERLY 20 TO 30 KTS, HOWEVER WINDS ARE DECREASING
WEST OF THE WAVE. AS THE WAVE CONTINUES TO TRACK TO THE WEST,
ENVIRONMENTAL CONDITIONS BECOME MORE CONDUCIVE FOR DEVELOPMENT.
4. THIS SUPERSEDES REF A.
5. THIS ALERT IS VALID UNTIL 151900Z.//
141905Z AUG 09
FM NMFC
BT
UNCLAS
MSGID/NMFC/OVLY2/0087/AUG
OVLY/TCFA/141830Z7/AUG/1OF1/TCFA AL9009/METOC
LINE/2//G/120000N3/0263000W1/120000N3/0303000W6
LINE/2//G/133600N3/0263000W1/101800N0/0263000W1
LINE/2//G/101800N0/0263000W1/101800N0/0303000W6
LINE/2//G/101800N0/0303000W6/133600N3/0303000W6
LINE/2//G/133600N3/0303000W6/133600N3/0263000W1
TEXT/20//G/091800N8/0283000W3/TCFA AL9009
TEXT/20//G/081800N7/0283000W3/VALID UNTIL 151900Z
TEXT/20//G/071800N6/0283000W3/WINDS: 20-25 KTS
TEXT/20//G/061800N5/0283000W3/MVG: W AT 8-13 KNOTS
ENDAT
BT
#0001
NNNN
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1124. Drakoen
Quoting weatherboykris:
So drak, what's ur thinking at this point?


I'm thinking it goes over the northern Lesser Antilles stay just south of Puerto Rico and then the shortwave should create a weakness for the system to head more poleward and end up in the HPC 7 day position. That's the thinking based on the latest model runs.
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Quoting cg2916:

Guys, it's illegal to access that info. Only NOAA can use it for official purposes.

If its for official purposes only, and illegal for us to access it, why isn't it behind a firewall or on an internal intranet network?

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Quoting WeatherStudent:


The gigantic kick eastward that the ECMWF is seeing with 90L. Mind you, IT'S the ONLY ONE forecasting this.


You can't say that wont happen. Its just another possibility in the mix here.
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Ok, I am not an english major.. but I do find this update a bit confusing??

SHOWER AND THUNDERSTORM ACTIVITY ASSOCIATED A BROAD AREA OF LOW
PRESSURE CENTERED ABOUT 250 MILES WEST-SOUTHWEST OF THE SOUTHERN
CAPE VERDE ISLANDS HAS BECOME A LITTLE LESS ORGANIZED OVER THE PAST
SEVERAL HOURS. HOWEVER...CONDITIONS STILL APPEAR FAVORABLE FOR
FURTHER DEVELOPMENT OF THIS SYSTEM...AND A TROPICAL DEPRESSION
COULD FORM DURING THE NEXT DAY OR TWO
AS IT MOVES WESTWARD AT NEAR
15 MPH. THERE IS A HIGH CHANCE...GREATER THAN 50 PERCENT...OF THIS
SYSTEM BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

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Quoting cg2916:

And I'm concerned about the chance that TD 2 and 90L hitting the same area one right after another. It's possible, but unlikely, though.
Never say never remember frances and jeanne 2004?
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1116. Melagoo


What a difference a week makes
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Is it me, or did these models go a tad bit more south?

Link
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This is a link to a webcam at 17N 25″W - Mindelo Harbor, (North side of Sao Vincete, Cape Verde)
Too far NE of 90L (11.7N 29W) to be cloud coverage from our invest, I would think - but an interesting picture, none the less.

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Quoting WeatherStudent:
Stupid model, that'll so NOT HAPPEN, that's for damn sure. It's really dissapointing this cane season thus far, let's see whether this trend continues, :).

You might be disappointed, but I am personally estatic here. A quiet season is a good season, in my book.
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1111. cg2916
Quoting Cotillion:


Link

That might be what you're looking for.

Guys, it's illegal to access that info. Only NOAA can use it for official purposes.
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Quoting Drakoen:
Be on your guard guys. AVG is picking up some Trojans


Yeah I just started running my virus scan
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Quoting weatherboykris:
Hannah...NHC has scheduled a possible recon flight for the remnants of TD-2 once it reaches 55W...

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.



It seems we may finally get them to fly over a system for the first time this season.
Member Since: July 19, 2008 Posts: 43 Comments: 4051
1108. LBAR
Quoting extreme236:


Huh? there is just the main cluster and the bands to the south.


Well, I'm no expert...haha...but learning a lot on here for sure. I just see two different clusters on the floater loop for 90L with what looks to me like the COC slightly nearer the one on the southwestern side.
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Thanks kris.
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Quoting Drakoen:
Be on your guard guys. AVG is picking up some Trojans


I just got that too.
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So drak, what's ur thinking at this point?
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1102. bwi
HPC's 3-7 day outlook final issuance for today now up.

Although HPC isn't going to go out on a limb on intensity, their discussion says the track ideas are coordinated with TPC. Looks like they estimate 90L just north of Haiti Day 7.
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Hi to all
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Quoting WeatherStudent:
Stupid model, that'll so NOT HAPPEN, that's for damn sure. It's really dissapointing this cane season thus far, let's see whether this trend continues, :).

what will so not happen?
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Quoting viman:

just basically the coordinates, estimate pressure, direction and distances and such, I started logging the information only when it was at TD status and I regretted that I just didn't do it from the beginning.


Link

That might be what you're looking for.
Member Since: August 23, 2008 Posts: 7 Comments: 5300
Can someone give me the SHIPS model. thanks
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Quoting hurricanehanna:
Hey Pat - question. Once a system is declared a TD or TS, how close in does it have to be for the HH to go investigate?


Normally the Low Level Reconisance (aka. NOAA 42 and 43) only goes out when it reaches 55W. The Gulfstream-IV can go out farther. Their base 3 bases of operations are Tampa, St. Croix and Barbados.
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I see we have a new one added....

Link
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1095. ackee
where is 90L centre se of the convection?
Member Since: July 15, 2008 Posts: 0 Comments: 1355
Hannah...NHC has scheduled a possible recon flight for the remnants of TD-2 once it reaches 55W...

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.

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i'm guessing 90L will be within 50 miles either north or south of Puerto Rico in 5-6 days.
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Quoting Thaale:
Yeah, but I've heard that hurricane windows may not breach even during a cat 5, but they and/or their frames do get all warped, scratched up, and permanently scarred if you let them go through a storm unprotected. Basically you have to then start over with a new set of $8000 windows. I don't know if this is still true or if the materials have gotten better of late or what - if anyone can contradict, please do. I do know that I don't see anyone with the resources to pick amongst various options choosing to go with just impact-resistant hurricane windows.

I do agree with you that the 100 mph spear-impact scenarios are very unrealistic. Isn't the Dade County standard something like, able to withstand a 2x4 at 34 mph? Even a 150 mph wind doesn't necessarily accelerate every heavy object it picks up TO 150 mph!

Exactly. Hurricane windows are great for large picture windows, but absolutely horrible for smaller panes. (they are too expensive for smaller panes) While the frame may get bent up with a direct impact, I would personally rather have a bent frame and have to replace a window for a good chunk of change, rather than have to total out a room or my house for a few dozen times the cost.

As for the scratches, its glass on both sides, with plastic in the middle, so scratches can be handled the same way as they would be with regular glass. (and if the frames get scratched, its a $20 fix... a can of paint and a brush, maybe some painter's tape))
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1090. Drakoen
Quoting weatherboykris:
So the NHC at this point appears to be leaning towards the "just north of PR" idea.


They still take it over the northern Lesser Antilles on day 6.
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1089. WxLogic
Quoting Drakoen:


If TD2 manages to regenerate it could be problematic. I'm more concerned with something that is 5 days away than something that is almost 10 days away.


Indeed...
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1088. viman
Quoting Patrap:
That Depend Hanna,I believe they can Stage in The Leewards for extended Atlantic Flight,maybe St Croix..but Im not sure as too the Range. I think there is a Longitude threshold Point for that


Thye do stage in ST. Croix, been to the hangar, and they usually start to fly when the systems hit 55degress
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1087. cg2916
Quoting Drakoen:


If TD2 manages to regenerate it could be problematic. I'm more concerned with something that is 5 days away than something that is almost 10 days away.

And I'm concerned about the chance that TD 2 and 90L hitting the same area one right after another. It's possible, but unlikely, though.
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1086. Drakoen
Quoting weatherboykris:
The HPC in consultation with the NHC is forecasting 90L to be just north of PR by Day 7..forecast came out 20 minutes ago...


http://www.hpc.ncep.noaa.gov/medr/day7nav.html


Very interesting.
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12z Euro still looks mighty fishy to me.
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So the NHC at this point appears to be leaning towards the "just north of PR" idea.
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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.