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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90L is rather classic looking
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Quoting IKE:
TWC is all over the tropics now. I was gonna say they were all over Ana, but that doesn't sound right...lol.


Hey Ike,
yeah, there goes quiet season and 2009 will not be 0-0-0 but it tried :)
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Seems like we are a few model runs away from a more accurate picture. They are not initialized fully imho.
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Morning Al and Ike
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4230. IKE
Quoting nrtiwlnvragn:


Morning Ike, keep your eyes on the area in the keys, pressure dropping.




I'm watching that too...
Member Since: June 9, 2005 Posts: 23 Comments: 37860
Good morning Weather
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Quoting IKE:
TWC is all over the tropics now. I was gonna say they were all over Ana, but that doesn't sound right...lol.


Morning Ike, keep your eyes on the area in the keys, pressure dropping.


Member Since: September 23, 2005 Posts: 15 Comments: 11343
4227. IKE
Look where the 6Z NOGAPS takes Ana...and strengthens it significantly....shutter up those windows WS!
Member Since: June 9, 2005 Posts: 23 Comments: 37860
how quickly things can change, this time last week

"nuttin"
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Morning Ike. A start to what looks like another busy day.
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Quoting IKE:
TWC is all over the tropics now. I was gonna say they were all over Ana, but that doesn't sound right...lol.

Morning Ike....please, not this early! ;)
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According to the SSD overlay for SSTs (which isn't always right, plus SST maps always have some differences), Ana should be hitting the slightly warmer waters in the next couple of hours.

But the slight increase seems to be all around 50W anyhow, from different maps and such. So, within the day.
Member Since: August 23, 2008 Posts: 7 Comments: 5300
Here's a good look at both systems...

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Sweet! I almost fell outta my bed reading TD2 survived and became a TS last night finally we have a name
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Hmmm CMC 00UTC spins up the blob south of Florida and tracks it into the Gulf. Not the most reliable model in years past, but wind shear seems not to be a hindrance and SST's are warm. Thoughts?
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4219. tkeith
Quoting hurricanehanna:

We've put Press in charge of giving him Thorazine! lol
I'm glad I didn't have a mouth full of coffee when I read that...lol

:)
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Some mid level spin with this wave S FL
Radar LOOP
Winds & PMSL
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1992 has a STS in April, which if it was today, would of been named.

So, discarding that, it is the latest start since 1984. (Also, had a STS before its first named storm but that didn't occur until August 18th.)

25 years.
Member Since: August 23, 2008 Posts: 7 Comments: 5300
4216. IKE
TWC is all over the tropics now. I was gonna say they were all over Ana, but that doesn't sound right...lol.
Member Since: June 9, 2005 Posts: 23 Comments: 37860
T.S. Ana

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Member Since: September 23, 2005 Posts: 15 Comments: 11343
Quoting aquak9:
poor weatherstudent's gonna have a complete breakdown before this is over...and he'll probably take a few of us with him...

We've put Press in charge of giving him Thorazine! lol
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Quoting tkeith:
GOM has plenty of warm water and very little shear, I wouldn't discount anything blowing there. It could get busy in a hurry around here...gonna keep my ears perked up for awhile gotten kinda complacent with June and July being so...ahem...uneventful.

Agreed. Time to check the oil in the generator. Hope some of the "sleepers" in here have their supplies ready
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4211. russh46
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We were one day away from tying the the latest date for a name storm to form since 1992, of course that is when the powerful Andrew form.
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4209. tkeith
Quoting hurricanehanna:
CMC model is still developing the GOM feature....brings ANA into the GOM too
GOM has plenty of warm water and very little shear, I wouldn't discount anything blowing there. It could get busy in a hurry around here...gonna keep my ears perked up for awhile gotten kinda complacent with June and July being so...ahem...uneventful.
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Wow I see a lot of new names this time around!
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Later bajelayman
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4205. Hhunter


hmmmmmmmmmmmm
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Ana is a comback story, just throw it in with others like Felix.

But 90L is looking amazing this morning

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4203. aquak9
poor weatherstudent's gonna have a complete breakdown before this is over...and he'll probably take a few of us with him...
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Quoting tkeith:
Looks like Ana's got a long row to hoe, but her and 90L seem to have their eye on me and you...

Good to see ya again ,I knew these storms would bring you out of hibernation...lol.


Yeah, I've been "lurking"for a while then posting the past few days when the activity picked up. A lot of the Gulf Coast bloggers have been posting....not liking what the models are showing...yikes!
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Good Morning.

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CMC model is still developing the GOM feature....brings ANA into the GOM too
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4199. tkeith
Quoting hurricanehanna:

Hey Tkeith! How are ya?
Woke up this AM to find Ana - thought for sure 90L would have been named first.
Looks like Ana's got a long row to hoe, but her and 90L seem to have their eye on me and you...

Good to see ya again ,I knew these storms would bring you out of hibernation...lol.

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I'm gone, see y'all later. Have a good day and get your supplies up to speed.
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The are no substantial signs of dry air intrusion occurring in Ana. Convection sporadically decrease and increase hither and thither in tropical cyclones. This system seem to be gaining magnitude, as the southern axis continues to expand. There is no major gap in the moisture field, indicating that the dry air has not penetrated it. Its outer moisture field should help remove the SAL dust ahead; Ana had dry air ahead throughout its life cycle.
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Quoting stormdude77:
Anyone notice the GFS forms another system behind 90L and it moves towards the Lesser Antilles again?

Damn....


We have a hairy few weeks, then months, ahead.
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So, where are my 0-0-0 friends this AM? lol
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Quoting bajelayman2:


You a 'chaser' or just happened to be in the hurricanes, where you were?


Yeah I started chasing hurricanes back in 2004, I has quite a surprise then, well thats when Central Florida saw 3 direct hits. Since then I have been going around.
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One fortunate thing as well, is the further west they go, the more unfavourable the MJO goes. The GFS/EWP diverge in forecasts after like today, but agree on the current conditions.
Member Since: August 23, 2008 Posts: 7 Comments: 5300
4192. WAHA

I have been tracking it's remnants. A STORM IS A STORM UNTIL IT IS ENTIRELY GONE, PEOPLE!!!
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Quoting tkeith:
4171. tornadofan 5:34 AM CDT on August 15, 2009

That's gonna keep me wet Sunday TFan...

Hey Tkeith! How are ya?
Woke up this AM to find Ana - thought for sure 90L would have been named first.
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Double Trouble: Ana forms; TD 3 developing
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Anyone notice the GFS forms another system behind 90L and it moves towards the Lesser Antilles again?

Damn....
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Quoting bajelayman2:


More dry air would be welcome at this time.


Definitely.

It's struggling at the moment, and it may not do much until 50W where the waters increase in temperature which can be problematic.

There's only really one bit of SAL left in the Atlantic. Fortunately, that's dead ahead of Ana which it'll have to battle through. May end up keeping a lid on it for the time being. However, it could be just doing dustsweeper duties for the storm(s) behind it.
Member Since: August 23, 2008 Posts: 7 Comments: 5300
Morning Stormdude77.

I am off shortly, breakfast and head out.
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Quoting tkeith:
Futuremet, what do you see that would turn these systems East as they near the Bahamas and Florida?

Some front coming down out of Canada?


A longwave trough migh curve it out to sea. However the models have been trending west over the past few days. A valid conclusion can be made from the GFS when all the ensembles are in consensus.
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Quoting weatherwiz:
Yeah, that is kinda dangerous to be close to the water in the height of the storm. I have been in many hurricanes, well not near the water but a few miles or so from the beach.


You a 'chaser' or just happened to be in the hurricanes, where you were?
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4184. tkeith
Futuremet, what do you see that would turn these systems East as they near the Bahamas and Florida?

Some front coming down out of Canada?
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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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