Ana and TD 3 take aim at the Lesser Antilles

By: Dr. Jeff Masters , 04:17 PM GMT on Αύγουστος 15, 2009

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Tropical Storm Ana was born this morning, when the remnants of Tropical Depression Two made a comeback and organized into the first tropical storm of the 2009 Atlantic hurricane season. Ana is the latest first named storm of the season since Hurricane Andrew got its name on August 17, 1992. The two storms have some similarities, as Andrew formed in the same part of the ocean, and also struggled in its early days with high wind shear and dry air. Let's hope the similarities end there.

Ana is struggling this afternoon. After an modest burst of heavy thunderstorm activity prompted NHC to upgrade Ana to a tropical storm early this morning, Ana has run into strong upper-level winds from the west that are creating high wind shear. This shear was not forecast, and it is not clear how long it will last. The shear has acted to drive dry air into the core of Ana, destroying almost all of Ana's heavy thunderstorms. The low-level center of the storm is now exposed to view, something that often foreshadows the death of a storm. It is possible the shear will destroy Ana, and several models (the GFS and ECMWF) forecast this may be the case. However, the shear forecast calls for shear to drop into the low range, 5 - 10 knots, tonight through Tuesday. If the shear does drop as forecast, Ana should be able to moisten the atmosphere around it sufficiently to protest itself from the dry Saharan air that surrounds it (Figure 1). SSTs are 27°C today, and will increase to 28°C by Sunday. By the time Ana moves into the Bahamas, total ocean heat content rises steeply (Figure 2), and rapid intensification of Ana is possible, if the shear and dry air haven't disrupted the storm. The intensity forecast models, for the most part, predict a steady intensification of Ana to the threshold of hurricane strength five days from now. The HWRF model is on the strong side, predicting a Category 2 hurricane. The GFDL predicts a weak tropical storm five days from now, but that is because the model has Ana passing over the rugged terrain of Hispaniola, something the other models do not predict. In summary, the intensity forecast for Ana has higher than usual uncertainty, and I give equal chances that the storm will be a hurricane--or non-existent--four days from now.


Figure 1. Water vapor image from this morning showing the large area of dry, Saharan air surrounding Ana, and lying to the north of Tropical Depression Three. Image credit: NOAA/SSD

Tropical Depression Three forms, could be Bill later today
QuikSCAT data from this morning and satellite loops revealed that the tropical wave (90L) in the middle Atlantic has finally developed a well developed surface circulation and can be classified as Tropical Depression Three. Recent satellite imagery suggests that TD 3 may already be Tropical Storm Bill. Water vapor imagery (Figure 1) shows that TD 3's center consolidated a few hundred miles south of the dry air of the Saharan Air Layer (SAL). Thus, the storm should not be affected by dry air and dust as much as Ana has been. Ana may also act to moisten the atmosphere in front of TD 3, helping protect the storm from the SAL as it edges farther north over the the three days.



Figure 2. Heat content of the ocean, in kJ per square cm. Oceanic heat content steadily increases for Ana and TD 3 as they approach the Lesser Antilles Islands. Oceanic heat content levels of 90 kJ per square cm are frequently associated with rapid intensification of hurricanes. Image credit: University of Miami.

Wind shear is moderate, 15 knots, but is forecast to fall to 10 - 15 knots on days 2 - 5. Sea Surface Temperatures are about 27.5°C, and will remain in the 27.5 - 28°C range the next five days. The combination of low wind shear and sufficiently warm SSTs should allow TD 3 to intensify steadily, and I expect the storm will be at hurricane strength by Wednesday, when it will be near the northern Lesser Antilles Islands. Most of our reliable intensity models strengthen TD 3 into a hurricane by Wednesday. Oceanic heat content (Figure 2) increases sharply just before the islands, so TD 3 could be intensifying rapidly as it moves through or just north of the Lesser Antilles on Thursday. TD 3 consolidated farther south than expected, so the track models calling for a more northerly path were probably incorrect. In particular, the ECMWF model, which had TD 3 turning sharply northwestward and missing the Lesser Antilles Islands, was probably much too far to the north in this morning's 00Z run. TD 3 will probably pass very close to the northern Lesser Antilles islands on Wednesday and Thursday.

I'll have an update Sunday.

Jeff Masters

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Im impressed.

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4013. Patrap
Member Since: Ιούλιος 3, 2005 Posts: 421 Comments: 127566
That wasn't unexpected....has the pressure lowered?
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4011. Drakoen
Quoting Stormchaser2007:
God forbid another blob forms in the Atlantic or we could be looking at another storm. lol


LOL ECMWF shows another two storms forming in the Tropical Atlantic over the next 10 days.
Member Since: Οκτώβριος 28, 2006 Posts: 57 Comments: 29888
Quoting superweatherman:
hey... weather456... soo what you think about TD4... you think it will make TS by 8PM like I said last night...


I could not find your question,

while it did not make TS status by 5 am, you still were close with TD 4.

My thoughts are with very low shear and warm ssts, only proximity to land would hinder development which is about 36-48 hrs away. This could easily become TS Claudette later today.

I will have a full update on my blog later this morning on all three systems.

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Quoting Stormchaser2007:
God forbid another blob forms in the Atlantic or we could be looking at another storm. lol


Unfortunately you'd only have to take a look at west africa and the models to know we got another one coming
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4008. jipmg
Quoting nola70119:
Hello all, been away for a few hours....looks like the Gulf blob is getting its act together.


yea its TD 4 now
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Quoting Stormchaser2007:
Tropical Depression 4


Not sure I trust the SHIPs on that. Given how fast it's spun up, and with all factors being conducive now, or at least most...

Only a 5mph increase in 12 hours? Or a 10 in 24 hours? Maybe due to land interaction, but it's not like it's near the mountains of Hispaniola.

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Quoting Drakoen:
This is crazy...


You can say that again Drak.....

I was just checking in to see before I went to bed and all I could say was "What the Heck is this....

Taco :0)
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4004. Ldog74
Quoting popartpete:
I would have to agree. Since the official forecasts are spaced every six hours, I've seen AOI's go to TS's without officially every having been a numbered TD. It must have been a TD at one point, it's a stage of genesis, but it can all happen very, very quickly. We are used to storms that take a while to develop and stay in TD stage for a while before being named. It's kind of confusing, but it is was easy, everybody would understand the tropics. I'd have to say that all of us combined are pretty smart...a think tank that is useful and amusing at times. Maybe the crow pic was a little over the top, but we could chalk it off to plain ol' innocent fun, as long as no one was hurt.


I believe youre missing my point. Forgive me if youre not. I am aware that there are cyclones which develop quickly enough so that they are never officially classified as a TD. And i understand that although the 6-hour updates never consider these systems to be TDs, they were TDs at one point. Those cyclones are not the ones I am talking about. In most cases a TD is a required aspect of cyclogenesis, but not all. In some instances, a weather system may have 40mph+ sustained winds, and not be a cyclone. If these winds do not diminish, and the LLC closes off, then the system is instantly a TS, and at no point in its development could ever have been considered to be a TD.
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Hello all, been away for a few hours....looks like the Gulf blob is getting its act together.
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God forbid another blob forms in the Atlantic or we could be looking at another storm. lol
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i projected TD4 by 8am it bet me by 5hours...It this continues it may be a cat 1 by 8pm Sunday..
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TS - Thanks for the blog update earlier - I love how you explain things using words I can understand. If memory serves, we had some fun talking baseball/football last year - nice to see you again.
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Quoting TampaSpin:
Claudette will be a hurricane before landfall .......amazing...WOW


DSHP has it going inland before?... what is DSHP?
Member Since: Αύγουστος 22, 2006 Posts: 2 Comments: 1975
Quoting Catfish57:
SC2007...Thanks for the link. Something seems amiss though..... Why was it showing intensification after going inland? Glitch maybe?


Im not sure. I havent really taken a good look at it. Im running too many radars and programs to really focus on something right now lol. Ill get to it in a bit.
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3997. Drakoen
Quoting Stormchaser2007:


How so?


This thing formed so fast. We have 3 systems in the Atlantic lol
Member Since: Οκτώβριος 28, 2006 Posts: 57 Comments: 29888
3996. Patrap
TD-4 JSL Image





Rainbow




BD DvoraK







Member Since: Ιούλιος 3, 2005 Posts: 421 Comments: 127566
Quoting HurricaneFCast:

How fast can the mid-level circulation reach the surface? Quickly, in the right conditions. Sometimes it only takes a matter of 6-12 hours, but that's one part of meteorology that is not easily predicted. Given the SST's, 10 knot wind shear, and moderate Ocean Heat Content within its forecast path, It should be a Tropical Storm within 24 hours as long as the environment remains favorable. The NHC will probably be a bit more proactive in naming this a Storm, too, given its proximity to land.


Not to burst your bubble, but it has a LLC and it's a tropical depression already.
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I see the SHIP has td4 it if its still out at sea at 62knots... by 120hrs
Member Since: Αύγουστος 22, 2006 Posts: 2 Comments: 1975
3993. jipmg
3 named storms in a matter of 3 days... wow
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Quoting Drakoen:
This is crazy...


what is drak???
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Quoting Drakoen:
This is crazy...


How so?
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Claudette will be a hurricane before landfall .......amazing...WOW
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HurricaneFCast yes that was it. thanks
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3988. IKE
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SC2007...Thanks for the link. Something seems amiss though..... Why was it showing intensification after going inland? Glitch maybe?
Member Since: Ιούλιος 29, 2009 Posts: 0 Comments: 72
Quoting btwntx08:

claudette at 11 am likely


Well, as it's so close to land at 35mph, it could be at any intermediate times.

They may issue TS watches for the immediate area.
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Very interesting.

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3983. Drakoen
This is crazy...
Member Since: Οκτώβριος 28, 2006 Posts: 57 Comments: 29888
Quoting Stormchaser2007:
Tropical Depression 4


wow. thank you storm
Member Since: Αύγουστος 22, 2006 Posts: 2 Comments: 1975
The winds fairly high in comparison to a fairly high pressure due to the high around Bermuda per the satellite analysis, I guess. Around 1016-18. Pressure gradients and such.
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3980. cjnew
Im in Panama City and I wont be sleeping either. thanks for the updates.
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CyberStorm, you've got mail
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3978. jipmg
its hitting DMAX in the Gulf of mexico
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Quoting stormsurge39:
HurricaneFCast how fast can that change?

How fast can the mid-level circulation reach the surface? Quickly, in the right conditions. Sometimes it only takes a matter of 6-12 hours, but that's one part of meteorology that is not easily predicted. Given the SST's, 10 knot wind shear, and moderate Ocean Heat Content within its forecast path, It should be a Tropical Storm within 24 hours as long as the environment remains favorable. The NHC will probably be a bit more proactive in naming this a Storm, too, given its proximity to land.
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hey... weather456... soo what you think about TD4... you think it will make TS by 8PM like I said last night...
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3975. Michfan
It takes a few for them to remove the invest.
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Does any one know how far it is to the closest point it could hit??? Please
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Crap... Cloud tops are 45,000 to 50,000 ft..

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Quoting DanielPC:
Link to Navy/NRL's report on TD4: Link


sorry i was behind the board, uh it also still has 91L on it :/
Member Since: Αύγουστος 22, 2006 Posts: 2 Comments: 1975
3971. Michfan
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Tropical Depression 4
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42013 - MARITIME-buoy
Sunday Aug. 16 - 4:40 UTC
Wind: SE at 29 mph
gusting to 31
Pressure: 1015.2 mb
Sea Surface Temp: 86.2°F
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Wow....We have had more action in the past 24 hours than we have had in the past 2 1/2 months combined. Hurricane season sure woke up on August 15, 2009.
Member Since: Ιούλιος 29, 2009 Posts: 0 Comments: 72
3967. IKE
Quoting Drakoen:


I don't blame you. This thing is really close and could really ramp up.


Think I'll go make a pot of java....
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no surprise check out Post 3955 for reference...
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3965. KEEPEROFTHEGATE (Mod)
2009 Storms
All Active Year


Atlantic
04L.FOUR
03L.BILL
02L.ANA

East Pacific
10E.GUILLERMO

Central Pacific

West Pacific
95W.INVEST
94W.INVEST
01C.MAKA

Indian Ocean

Southern Hemisphere
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3964. Drakoen
Quoting IKE:



Not sure I can go back to sleep.


I don't blame you. This thing is really close and could really ramp up.
Member Since: Οκτώβριος 28, 2006 Posts: 57 Comments: 29888

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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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