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 tea3781:
Its moving due west right now. I think the convection is building to the southwest and thats what you are seeing.

Time Lat Lon Wind(mph) Pressure Storm type
------------------------------------------------------------------------
04 GMT 08/15/09 14.6N 45.8W 35 1005 Tropical Depression
09 GMT 08/15/09 14.6N 46.8W 40 1005 Tropical Storm


Okay, hope the official track is right.
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4133. JRRP
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4132. aquak9
g'morning ya'll.

errr...is it a good morning?
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4131. Walshy
Quoting WeafhermanNimmy:
Why is invest 90L not a tropical depression yet...

It has an intensity of 30 knots....


Needs a well deformed circulation. Should be a depression later today.
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Yeah, Ana is not moving WSW. She is moving west.
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Quoting IKE:


Hi Ike, I think the loop shows it keeping lower than that track, no?
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Why is invest 90L not a tropical depression yet...

It has an intensity of 30 knots....
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Quoting IKE:


Morning....

Finally.....after 76 days......

1-0-0


I'll pop the cap off the OJ bottle :) Not liking the track though and you know SFL people will go nuts later today.
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4126. tea3781
Its moving due west right now. I think the convection is building to the southwest and thats what you are seeing.

Time Lat Lon Wind(mph) Pressure Storm type
------------------------------------------------------------------------
04 GMT 08/15/09 14.6N 45.8W 35 1005 Tropical Depression
09 GMT 08/15/09 14.6N 46.8W 40 1005 Tropical Storm
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And assuming it keeps up it's current trend, it's likely we'll see TD3 later today, also.
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Can someone post that site where it shows the Track History and the Intensity Forecast in a table?
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THE INITIAL MOTION ESTIMATE IS 270/14. THE GLOBAL MODELS ARE IN
AGREEMENT THAT A DEEP-LAYER RIDGE WILL STRENGTHEN NORTH OF THE
TROPICAL CYCLONE OVER THE NEXT DAY OR SO. THIS PATTERN FAVORS THE
TRACK OF ANA GRADUALLY BENDING FROM A WEST TO A WEST-NORTHWEST
DIRECTION WITH AN INCREASE IN FORWARD SPEED. THE ONLY SIGNIFICANT
OUTLIERS TO THIS TRACK ARE THE GFDL AND GFS...WHICH BOTH WEAKEN THE
SYSTEM RATHER QUICKLY...LEADING TO A MORE WESTWARD TRACK OF THE
CYCLONE. IN A FEW DAYS...SOME OF THE MODELS...SUCH AS THE GFS...
SHOW A WEAKNESS IN THE RIDGE OVER THE WESTERN ATLANTIC THAT COULD
ALLOW THE CYCLONE TO GAIN A LITTLE MORE LATITUDE. THIS WEAKNESS
APPEARS TO BE CAUSED BY THE MID- TO UPPER-LEVEL LOW CURRENTLY NEAR
25N 65W. HOWEVER...THE MAJORITY OF THE GUIDANCE SHOWS THE MID- TO
UPPER-LEVEL LOW MOVING WEST-SOUTHWESTWARD WITH MINIMAL INFLUENCE ON
THE STRENGTH OF THE RIDGE. GENERALLY...THE MODELS THAT HOLD ONTO
ANA ARE IN GOOD AGREEMENT THROUGHOUT THE FORECAST PERIOD. THE NHC
TRACK FORECAST IS SHIFTED TOWARD THE SOUTHWEST FOR THIS ADVISORY...
BUT NOT AS FAR AS THE MODEL CONSENSUS.

So, expected to gain latitude pretty soon. Of course, it also depends on intensity. Stronger it gets, more north it'll probably go.
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From the looks of it, maybe early to say, but I think that the expected TD3, or Bill, is going to be a monster.
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Check out long range radar loops from Miami or Key West. Hint of spin in that blob, maybe? Something could develop right under our noses in the bathwaters of the Gulf this weekend.
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Quoting washingaway:
Both systems seem to going wsw. Does anyone else see this?


Yes, I noticed this from last night, I personally think that they will stay South of the forecast track and barrel through the islands.
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4118. Walshy
Current 1-0-0

Ana becomes weak hurricane.

1-0-1

Bill forms and strengthens.

2-1-2
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just the forecast track on stormpulse, what are the possibilties of a track 5 days out being true? Thanks
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Quoting Cotillion:
Interesting to see when Ana gets past 50W (Probably sometime today) as the waters begin to get warmer.

Won't it be?!

Thanks Nimmy!

Night all, I've got about 2 hours until I have to get up to go fishing! :)
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Quoting HurricaneFCast:


OH! And Nimmy, Congrats man! UC-Davis is an excellent university!


Thanks! You guys are really nice ppl...I should come here more often! :)
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Interesting to see when Ana gets past 50W (Probably sometime today) as the waters begin to get warmer.
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Quoting WeafhermanNimmy:


Well Max, it's not going to be expensive becuase they can give you $20,000 stipend!!! However, it's very competative to get in!

Well, we do weather and just a lot of ozone study, basically!


OH! And Nimmy, Congrats man! UC-Davis is an excellent university!
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Both systems seem to going wsw. Does anyone else see this?
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Quoting Hurricane4Lex:
PS is there a fujiwara effect if we have Ana and Bill?

They are certainly close enough, however there are a couple of inhibiting factors hindering an interaction between the two.
First, Ana is due to pick up forward speed in the next couple of days, increasing the distance between the two systems.
Second, neither system is organized enough, nor strong enough, to have an influence on the other at the moment.

Therefore, unless Ana slows or one of these systems significantly strengthens, I don't see any significant, or even moderate, influence as a result of the fujiwhara effect during the life of these systems. I wouldn't rule out a mild influence, however.
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Quoting Hurricane4Lex:
PS is there a fujiwara effect if we have Ana and Bill?


I don't think it'll happen. They have only minimal effects on each other now, and Ana's expected to have an increase in forward speed.
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Quoting WeafhermanNimmy:


Well Max, it's not going to be expensive becuase they can give you $20,000 stipend!!! However, it's very competative to get in!

Well, we do weather and just a lot of ozone study, basically!

Well 20k doesn't mean much when tuition and other expenses exceed 30-40k.. I've learned that much at Miami lol. With my scholarships and grants, etc.. I had 42k in funding, but I still had to pay them like 2 or 3k out of pocket.. Total cost of attendance is just crazy! I couldn't get some of the grants at OU that I could at UM (certain in-state grants that were worth 2 or 4k).. It was about the cost for me, honestly I would have been accepted pretty much anywhere with a 4.0 GPA, but I chose UM because of its location, financial aid, and academic offerings. OU is an awesome school though!! I wouldn't mind going there for grad school at all!
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PS is there a fujiwara effect if we have Ana and Bill? P.M. me on Wunder mail for an answer
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Night all (or actually mornin) I'm going to sleep can tell this morn at sunrise will be crazy and then will be insane thereafter.

Safe wishes out to friends and family in the leewards, virgins, puerto rican isles
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6Z NAM shows a very weak Ana near Hispaniola 84 hrs out.
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Quoting HurricaneFCast:

No worries, It's all new this year! CIMSS completely overhauled their website in the "off-season".


Awesome.

Looks like it's time for me to re-learn the site, since the seasons picking up now, haha.
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Lol Okay, I didn't mean to quote my own statement. I think I need to go to bed.. It's 5am here and I'm supposed to be going fishing at 7:30. L. O. L.
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Did they change the duration of the watch/warnings?

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Quoting HurricaneFCast:

I considered U of OK for awhile, but they just were too expensive for out of state, and didn't offer many scholarships as compared to University of Miami. Plus, I live in Florida so it's much closer, the NHC is down there, it has beaches.. Etc.. :)
So what do you all focus on, then? No specific form of Weather?


Well Max, it's not going to be expensive becuase they can give you $20,000 stipend!!! However, it's very competative to get in!

Well, we do weather and just a lot of ozone study, basically!
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Quoting HurricaneFCast:

I considered U of OK for awhile, but they just were too expensive for out of state, and didn't offer many scholarships as compared to University of Miami. Plus, I live in Florida so it's much closer, the NHC is down there, it has beaches.. Etc.. :)
So what do you all focus on, then? No specific form of Weather, just the Dynamics of the Atmosphere in general, I mean?
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Quoting WeafhermanNimmy:


Well Atmospheric Science...yes....It's really nice to study out in Cali...the faculty are nice...:) Im really hoping to go to U of OK...for grad school or U of IL Urbania Champagne!

I considered U of OK for awhile, but they just were too expensive for out of state, and didn't offer many scholarships as compared to University of Miami. Plus, I live in Florida so it's much closer, the NHC is down there, it has beaches.. Etc.. :)
So what do you all focus on, then? No specific form of Weather?
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Quoting TropicalWxWatcher:


Thanks!

I recently got a new computer, so I lost all my tropical links. I was not aware of that overlay or the name switch.

No worries, It's all new this year! CIMSS completely overhauled their website in the "off-season".
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Quoting HurricaneFCast:
Try CIMSS. It has OHC (Formerly TCHP) overlay maps avaliable. Nice website they have with almost every overlay imaginable from satellites to models to OHC... Here's the link:

Link


Forgot to mention.. It's easiest to click on the active storm, and then you'll see the overlay options at the top of the screen. Ocean Heat Content is on the second row, next to the "Ocean:" overlays. It reads "OHC (RSMAS)" where RSMAS is Rosenstiel School of Marine and Atmospherics Science (University of Miami)
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Quoting HurricaneFCast:
Try CIMSS. It has OHC (Formerly TCHP) overlay maps avaliable. Nice website they have with almost every overlay imaginable from satellites to models to OHC... Here's the link:

Link


Thanks!

I recently got a new computer, so I lost all my tropical links. I was not aware of that overlay or the name switch.
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Try CIMSS. It has OHC (Formerly TCHP) overlay maps avaliable. Nice website they have with almost every overlay imaginable from satellites to models to OHC... Here's the link:

Link
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The NHC has never ever been wrong on intensity forecasts...NOT!!!...Hell, so far this year they even predicted Guillermo and Felicia to not even become hurricanes. Epic FAIL. They even admit they are terrible at forecasting intensities, mainly because the models are so bad at it. If I lived in the Antilles or Bahamas or Florida I would expect the unexpected.
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Ana could be a gulf coast storm too. First one that gets to the gulf loop wins the prize. I really hope she goes up the east coast fishing.
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Quoting HurricaneFCast:

Nice! You're majoring in meteorology, then? What's it like to study out there in Cali?


Well Atmospheric Science...yes....It's really nice to study out in Cali...the faculty are nice...:) Im really hoping to go to U of OK...for grad school or U of IL Urbania Champagne!
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Quoting Cotillion:


the Bahamas and around the SE Florida have very high THCP and SST waters. I'm afraid it wouldn't be out of the question for it to bomb around there. It's certainly happened before.



Thanks Cotillion. Yes, it definitely has happened before, I can remember many storms in which it has occurred. Hopefully the speed forecast as you mentioned does not allow this to occur.

Speaking of TCHP, do you know where I can possibly have a look at these data maps? I used to get TCHP data off of here , but it has not updated since last May. Is there another public source online at which one can view such data?

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Quoting WeafhermanNimmy:


OMG Me too! :) I would love to do that...Im a fourth year student UC Davis! :)

Nice! You're majoring in meteorology, then? What's it like to study out there in Cali?
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000
WTNT42 KNHC 150840
TCDAT2
TROPICAL STORM ANA DISCUSSION NUMBER 13
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022009
500 AM AST SAT AUG 15 2009

SATELLITE IMAGES INDICATE THAT THE TROPICAL DEPRESSION HAS CONTINUED
TO BECOME BETTER ORGANIZED AND IS NOW UPGRADED TO TROPICAL STORM
ANA. THE STORM IS DISPLAYING IMPROVED BANDING IN THE WESTERN
SEMICIRCLE ALONG WITH A BALL OF CONVECTION NEAR THE CENTER. NOAA
BUOY 41041 REPORTED A MINIMUM PRESSURE OF ABOUT 1005 MB AS THE
DEPRESSION PASSED VERY NEAR THE BUOY. THE INITIAL INTENSITY IS
RAISED TO 35 KT FOR THIS ADVISORY IN AGREEMENT WITH DVORAK
INTENSITY ESTIMATES FROM SAB AND TAFB.


I agree with that last statement if that's what they are solely looking at.
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On the track, it's also going right near the northern coast of Haiti.

That place, especially after last year, really does not need anymore.
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4088. KEEPEROFTHEGATE (Mod)
well time for a little nap let the morn crew have it for a couple of hrs

remember models are meant to be used as guidance only and do not depict final outcome for any one event things can and will change

now would be a good time to go over hurr. plans and begin first steps of gettin ready more so for our leeward island friends at the moment
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Quoting HurricaneFCast:

Probably just Severe Weather in general, I also have heavy interest in Tornadoes and Severe Thunderstorms. Definitely Tropical Weather as well, though!


OMG Me too! :) I would love to do that...Im a fourth year student UC Davis! :)
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Quoting WeafhermanNimmy:


Way to go your speciality will most likely be Tropical Weather right?

Probably just Severe Weather in general, I also have heavy interest in Tornadoes and Severe Thunderstorms. Definitely Tropical Weather as well, though!
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I'm hoping no GOM either check out the SST for the GOM
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Very interesting....I totally agree with the discussion b/c the DVORAK reading jumped from 1.5 to 2.5 this morning. I just dont really get why last Wed they didnt upgrade it to TS Ana.
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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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