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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4784. jipmg
GFS was turning that wave into a storm and hurricane rapidly and right behind TD 3
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Well, if I had to guess, I would say TD3 would roughly follow the same track as Ana.
Member Since: April 26, 2009 Posts: 3 Comments: 3667
4781. jipmg
Quoting kmanislander:
The center of Ana is now almost totally exposed allowing dry air into the core from the N and NW.

I will be back a little later to see how this plays out.



I dont think its going to look too good until the sun sets
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Wow i see a tropical wave emerging of Africa, might be Cladette? lol.
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LOL where all most up too 100 pages
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Quoting Weather456:
do you guys realise the models are going to shift now Td 3 has form right?

the 12Z runs will be more than interesting.

and stop looking at the 00Z runs over 12 hrs old, the 12Z is coming up.
thank you...people need to sto pinpointing on models 7-10+ days out (as you said, especially on models that were initialized before classification).
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The center of Ana is now almost totally exposed allowing dry air into the core from the N and NW.

I will be back a little later to see how this plays out.

Member Since: August 19, 2006 Posts: 0 Comments: 15816
Quoting P451:
MODIS caught the new Africa wave - which the GFS wants to develop into a hurricane that follows TD3(soon to be TS and Hurricane itself).



nice pic. indeed models have and are showing this to be a possible storm
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Quoting Ameister12:
There's a new wave coming off of Africa that looks menacing.




OMG. look at the size of it compared to Ana and TD3
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Quoting extreme236:


Ensemble models for a storm that is just now being declared a TD? A bit too early for that.


GFS ensemble models mean change each run...
Member Since: July 19, 2008 Posts: 43 Comments: 4051
Quoting AussieStorm:


What's that developing in the GOM?


Look at key west radar you'll see what I think may be humberto's cousin as someone put it
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So i see we have T.S Ana, wow!, which might be a threat to SFLA. and 03L is there still the possibility of a SFLA hit?
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Quoting IKE:


I clicked it....same results....I'll delete the link.....


Hey, I got it to work. Had to install 32bit and 64bit java....I got to track down all my explorer shortcuts and just use 64bit.
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There's a new wave coming off of Africa that looks menacing.



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Quoting CaneWarning:


Look at the ensemble models! They say fish.


Ensemble models for a storm that is just now being declared a TD? A bit too early for that.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
4766. jipmg
Quoting CaneWarning:
What a relief!


I wouldn't call it a relief.. the models can easily change
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Quoting CaneWarning:


Look at the ensemble models! They say fish.



so what that dos not mean any thing right now
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Good Morning (sort of)

That F5 event here on the blog last night certainly slowed me down this am.

CRS
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Quoting Weather456:
do you guys know the models are going to shift now Td 3 has form right?

the 12Z runs will be more than interesting.


Well never mind what I just said then!
Member Since: April 26, 2009 Posts: 3 Comments: 3667
4762. KBH
this weekend seems like the thriller weekend, all the bad weather is waking up... TD 1, 2, 3, plus there is a little blob that's gonna bring some TS to the southern caribbean B'dos and TnT
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06Z UKMET
Member Since: July 19, 2008 Posts: 43 Comments: 4051
Quoting nrtiwlnvragn:
Might see NHC shift a little south towards TVCN at 11 AM




Quite possible. They like to follow the LGEM and TCVN.
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Quoting SwirlOfDoom:
Lurk Mode OFF

How does the NHC come up with the various codes for Invests? Like what does 99L mean? Thanks for answering!

Lurk Mode ON


i wont answer you.

kidding hehe... they go thru 90-99, 99L just means they've gone thru 90-98 and are up to 99. i guess the L means low but that's just me talking.


'L' North Atlantic
'E' Northeast Pacific
'C' North Central Pacific
'W' Northwest Pacific
'P' South Pacific
'S' Southern Indian Ocean
'N' Northern Indian Ocean (Antiquated)
'A' Arabian Sea
'B' Bay of Bengal
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do you guys realise the models are going to shift now Td 3 has form right?

the 12Z runs will be more than interesting.

and stop looking at the 00Z runs over 12 hrs old, the 12Z is coming up.
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Quoting jasoniscoolman10:


90L IS NOT A FISH STORM YET..u are away of on this storm


Look at the ensemble models! They say fish.
Member Since: April 26, 2009 Posts: 3 Comments: 3667
4755. Bayside
Quoting P451:


90L is being renamed to 03L.

They'll make it official at 11AM I don't think they'll issue a special advisory with just 90 minutes to go. Maybe they will. Seems trivial.

We have TD3. Will probably be Bill by 5PM though the way this thing is getting it's act together.
Quoting P451:


90L is being renamed to 03L.

They'll make it official at 11AM I don't think they'll issue a special advisory with just 90 minutes to go. Maybe they will. Seems trivial.

We have TD3. Will probably be Bill by 5PM though the way this thing is getting it's act together.


Thanks!
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I rather see Florida in the 5 day cone now because like last year with Ike, it totally missed us. Any trending to the north can mean trouble for the Carolinas. A recurvature of TD3 will mean big trouble for the east coast possibly. I see that a Floyd recurvature is possible with the Florida east coast being spared.
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Quoting P451:


CMC does.



What's that developing in the GOM?
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Also, don't forget, there was a plane in Ana yesterday. The current models and NHC track guidance have real time upper air data in them.
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Might see NHC shift a little south towards TVCN at 11 AM


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Quoting FSUstormnut:


key west radar,.. you are 100% correct, this will form and hit the upper gulf. hopefully nothing too big


New Orleans/ Mississippi area Monday?
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I suppose one could say that yesterday, lots of folks were concentrating so much about the cat (90L, Bill-to-be) that they forgot about the mouse (Ana) when the "mouse" was just a remnant low.

I suppose folks in the Leewards and Puerto Rico area will be busy these next few days, awaiting the "mouse" and then the "cat".
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Quoting Weather456:
90L is a beast, now I see what the models were saying
Please explain?
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Quoting Brallan:
Is Ana going back to TD status?


Yup.
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What a relief!
Member Since: April 26, 2009 Posts: 3 Comments: 3667
Morning all. Looks like Ana will go south of Florida. TD3 seems like it'll head north of PR and still be a threat though.
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It says Invest 03L because the NHC hasn't officially put "TD" in the file.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Are there any models forming something in the GOM this weekend or early next week? Local mets seem to be down playing to just alot of rain. It sounds different on this blog. Thank you.
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Triplets, lol

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Quoting Weather456:
TS Ana sure is low



if it brings it thru south of PR, then we're off to a pretty interesting couple of days
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Quoting Brallan:
Is Ana going back to TD status?


No.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
4736. JRRP
Link
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Quoting FSUstormnut:


where are you seeing this?


AL, 03, 2009081512, , BEST, 0, 115N, 333W, 30, 1006, DB, 34, NEQ, 0, 0, 0, 0, 1011, 200, 45, 0, 0, L, 0, , 0, 0, INVEST, M,

invest_RENUMBER_al902009_al032009.ren
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4734. jipmg
the ensemble models all take TD 3 out to sea
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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.