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 Camellia1356:
If 02L and 90L grow to TS at the same time, how are the names allocated?


Pretty sure TD2 would get the name.
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1283. Drakoen
Quoting Camellia1356:
If 02L and 90L grow to TS at the same time, how are the names allocated?


02L gets named first
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When models are looking at a long-range cyclone and the timing/strength of a trough is involved, there will ALWAYS be either an outlier or two, two different camps of models, or "the fountain spray effect." Once 90L/Whatever gets closer and especially after the HH or NOAA have been able to fly it, we will know more. I am not betting on ANY model run for this system until we have good upper atmospheric data on the trough and the cyclone itself.

The NHC knows that some of the models are better in certain climatic conditions than others. The atmospheric setup in 2008 was different from what it is in 2009, so I don't think the Euro's credibility with this storm can be extrapolated based strictly on that. Again, the NHC knows what conditions each model does best in, and when they designate this TD3 and start posting a track, we'll get a better idea of which models they are giving more credit to.

As a Gulf Stater I have a personal interest in NOT seeing a major hurricane get into the hot tub and blow up to a probable Category 5 before slamming the central coast, but right now there are more credible models that have predicted that outcome than predicted the Euro outcome of a fisherman/woman. Even more seem to be predicting an East Coast problem. The Euro is the outlier, and unless/until the NHC sees it differently, it should be treated as such.
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No it just has issues. Look at the water vapor imagery and you can see dry air pushing up into it.

Yeah i see it....but i remember the models were predicting ideal conditions and the NHC had it developing almost instantly they gave it a high chance to develop in the next 48 hours and that was 48 hours ago....
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1280. Drakoen
Conditions by the Lesser Antilles and Bahamas are forecasted to be very conducive for development. The SHIPS shows very high TCHP
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1278. Patrap
Latest SAL Split-Window
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1277. hahaguy
Quoting futuremet:
Bookmark this link, it has all of the tropical radars. You will need to ask again

Thanks for the link.
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If 02L and 90L grow to TS at the same time, how are the names allocated?
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Quoting WxLogic:


Could be classified as TD3 by 5PM or 11PM tonight.

DMAX on both of these system will be interesting indeed. DMIN should be doing its handy work anytime now.
if there is no renumber very soon, there will be no new TD at 5PM.
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Quoting canesrule1:
then why are u selecting me if there are other people disregarding, I'm not using that model because it's an "outlier" and i usually discard them.


I was actually directing it at WS...but there are several people to whom it could be applied. Look, my point is is that if the Euro is telling me one things, and the dime a dozen statistical models(such as the BAMs, LBAR, etc.) are telling me something else, well, based on my years of (amatuer) experience, it's a no-brainer which one I'll lean towards. In this case, with the GFS, GFDL, HWRF and other high end models siding with the statisticals, I think that the more southern track is correct. I'm just making a point that you shouldn't totally disregard one of the best models out there just cause u don't like it.
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1273. doubles
This Orlando resident will be prepping (with 90L in mind) this weekend.

The fact that it's so huge means I'm likely to see something. Especially if it goes south I'll be in that dreaded NE quadrant.

Better to be safe than sorry, Floridians.
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Bookmark this link, it has all of the tropical radars. You will need to ask again
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1270. Drakoen
Quoting louisianaboy444:
90L is suffering from easterly shear and dry air

Are you beginning to believe this storm might not be the big monster it was hyped up to be


No it just has issues. Look at the water vapor imagery and you can see dry air pushing up into it.
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Quoting OSUWXGUY:
TD2's warm core is nicely vertically stacked!

Red line is where the storms is at... The temperature anomaly to the ambient environtment is displayed.



Thanks for the link *bookmarked*
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90L is suffering from easterly shear and dry air

Are you beginning to believe this storm might not be the big monster it was hyped up to be
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1266. scCane
http://www.nhc.noaa.gov/

the invest is less organized now, personally I see former td2 reaching ts Ana than the invest right now its looks like a sheared mess.
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1265. Patrap
Floater IR Loop,FLASH,GOM,Fla
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1264. WxLogic
Quoting Drakoen:


12.5N 28.8W. The system has yet to acquire a well defined circulation.


Could be classified as TD3 by 5PM or 11PM tonight.

DMAX on both of these system will be interesting indeed. DMIN should be doing its handy work anytime now.
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Quoting weatherboykris:


I'm not being an a$$...just saying, that some people are selectively disregarding models that don't fit their fantasies....this blog "hasn't become" any different than since I started blogging here three years ago...actually, the discussion has been much more civil than yrs past, IMO.
then why are u selecting me if there are other people disregarding, I'm not using that model because it's an "outlier" and i usually discard them.
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Quoting alaina1085:


Thats crazy how tightly clustered they are for this storm being so far out, not to mention its not even a depression yet.


It's all the same model, with different conditions. That's why they are so bunched.
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1261. Drakoen
90L is suffering from easterly shear and dry air
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1260. WxLogic
Quoting OSUWXGUY:
TD2's warm core is nicely vertically stacked!

Red line is where the storms is at... The temperature anomaly to the ambient environtment is displayed.



Nice cross section...
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Quoting ackee:
CAN I get link to this site please


http://raleighwx.easternuswx.com/models/atcf.html
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Quoting weatherboykris:


I'm not being an a$$...just saying, that some people are selectively disregarding models that don't fit their fantasies....this blog "hasn't become" any different than since I started blogging here three years ago...actually, the discussion has been much more civil than yrs past, IMO.


Models have there good days and bad days, most are bad days when you consider how long range people are talking about. 7-8 days you can throw the end right out the window. Remember there models not reality. i dont believe any of them that far out. 1-3 yes there a possibility, but remember weather patterns change very quickly especially in tropical regions, thunder storms can appear in 10 mins.
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Quoting ackee:
CAN I get link to this site please

it has it on this site.

just click on the invest then it will show the ensamble members up top. then click on it to view.
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1254. Patrap
Thanx for that Kris,..thats a tight cluster for sure
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1253. Drakoen
Quoting stoormfury:
Drak
where is the centre of 90L. IT is not as dicernable as earlier? and is the system moving south of west?


12.5N 28.8W. The system has yet to acquire a well defined circulation.
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not this year?

how can you tell? lol. there haven't been any storms for it to track.

just cause you always want the storm to hit S. FL and disregard any model that shows it going elsewhere doesn't mean that they aren't reliable.
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1251. ackee
Quoting weatherboykris:
12z GFS Ensembles...

CAN I get link to this site please
Member Since: July 15, 2008 Posts: 0 Comments: 1346
TD2's warm core is nicely vertically stacked!

Red line is where the storms is at... The temperature anomaly to the ambient environtment is displayed.

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Quoting canesrule1:
hey know it all, i don't care if 90L comes over miami or not, I am not a believer in that model and i don't care about it, anyways that was my honest opinion ans now you want to be a big a$$ about it, jesus christ what the hell as this blog become! sheesh!


I'm not being an a$$...just saying, that some people are selectively disregarding models that don't fit their fantasies....this blog "hasn't become" any different than since I started blogging here three years ago...actually, the discussion has been much more civil than yrs past, IMO.
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Quoting weatherboykris:
12z GFS Ensembles...



Thats crazy how tightly clustered they are for this storm being so far out, not to mention its not even a depression yet.
Member Since: August 2, 2006 Posts: 0 Comments: 1240
1245. Drakoen
02L models. Even if it becomes a strong hurricane the BAMD turns it back west. Definitely something to watch:

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Quoting chevycanes:

guess you guys missed this from the blog discussion.

The ECMWF was by far the most reliable model for forecasting hurricane tracks last year
it is an "outlier" model so I usually discard it.
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i dont think nothing will come from the system in the gulf this weekend maybe just a rain maker but farther down the line is a different story
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NOUS42 KNHC 131300
WEATHER RECONNAISSANCE FLIGHTS
CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.
0900 AM EDT THU 13 AUGUST 2009
SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)
VALID 14/1100Z TO 15/1100Z AUGUST 2009
TCPOD NUMBER.....09-077

I. ATLANTIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
2. OUTLOOK FOR SUCCEEDING DAY.....NEGATIVE.

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


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Drak
where is the centre of 90L. IT is not as dicernable as earlier? and is the system moving south of west?
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1237. KEEPEROFTHEGATE (Mod)
UNCLASSIFIED

--------------------------------------------------------------------------------

TROPICAL CYCLONE FORMATION ALERT

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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Quoting weatherboykris:


You all do realize just how reliable the Euro is historically, correct? Just cause it's not predicting CAT 5 IN MIAMI!!!!! doesn't mean it's a joke.
hey know it all, i don't care if 90L comes over miami or not, I am not a believer in that model and i don't care about it, anyways that was my honest opinion ans now you want to be a big a$$ about it, jezz what the hell as this blog become! sheesh!
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12z GFS Ensembles...

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Link to Cuban Radar?
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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