Danny weakens further; 94L worth watching

By: Dr. Jeff Masters , 1:54 PM GMT on August 28, 2009

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Tropical Storm Danny continues to weaken, and may merely be a tropical depression. Data from the Hurricane Hunters early this morning showed top winds of just 40 mph at the surface, and satellite intensity estimates of Danny's strength are now rating the storm a tropical depression. Danny looks very disorganized on satellite imagery (Figure 1), with the low-level circulation center exposed to view. There is no heavy thunderstorm activity near Danny's center, and only a small area of heavy thunderstorms lying several hundred miles east of the center.


Figure 1. Morning satellite image of Danny, showing the exposed swirl of clouds where Danny's center is, well displaced from the heaviest thunderstorm activity to the east.

The forecast for Danny
With wind shear at 15 knots this morning, and forecast to increase to 20 knots tonight and 30 knots Saturday morning, is is unlikely Danny will be able to strengthen to more than a 50 mph tropical storm. Dry air from the upper-level low that has been keeping Danny disorganized continues to be a problem for the storm, as well. The GFDL and HWRF models continue to insist Danny will strengthen to a strong tropical storm or weak Category 1 hurricane, but this seems very unrealistic given Danny's current struggles. With Danny's heavy thunderstorms all on the east side of the storm, it is unlikely that New England will feel tropical storm force winds from Danny when it scoots past on Saturday. Large swells from Danny creating high surf along the beaches of New England will be the primary hazard from the storm.

Massachusetts hurricane history
Two tropical storms have affected Massachusetts in the past decade, though neither of these storms brought sustained winds of tropical storm force (39 mph) to the state. Tropical Storm Beryl of 2006 just missed Cape Cod as a weak tropical storm with 45 mph winds. Beryl brought wind gusts to tropical storm force to Nantucket Island, and a 1 foot storm surge. Tropical Storm Hermine hit southeast Massachusetts on August 31, 2004, as a minimum-strength tropical storm with 40 mph winds. No land stations in Massachusetts reported tropical storm force winds during Beryl. The last time Massachusetts measured tropical storm force winds was in 1991 during Hurricane Bob, which hit Rhode Island as a Category 2 hurricane. Provincetown, Massachusetts measured sustained winds of 98 mph, gusting to 115 mph, and Buzzard's Bay received a 15 foot storm surge.


Figure 2. Tropical wave 94L, a few hundred miles west of the Cape Verdes Islands.

Invest 94L
A well-organized tropical wave (94L) lies a few hundred miles west-southwest of the Cape Verdes Islands. This disturbance has shown little change this morning. This morning's QuikSCAT pass shows a complete circulation, elongated in the east-west direction, with top winds of 30 mph. Satellite imagery shows only a small amount of heavy thunderstorm activity near the circulation center, but considerable thunderstorm activity south of the center. Shear is low, about 10 knots, and is expected to remain low to moderate, 5 - 15 knots, over the next five days. The waters are warm enough to support development, 28°C, and are expected to remain in the 27 - 28°C range over the next five days. The dry Saharan Air Layer (SAL) lies about 200 miles to the north and west of 94L, and it appears from water vapor satellite imagery that a modest amount of dry air from the SAL is now being ingested into the storm, slowing development. Dry air will continue to slow development until 94L's heavy thunderstorm activity can moisten the atmosphere enough to shield the storm from the Saharan Air Layer. NHC is giving 94L a medium (30 - 50% chance) of developing into a tropical depression by Sunday. The GFDL and SHIPS models both predict 94L will be a Category 1 hurricane five days from now. However, the HWRF model does not develop 94L. Most of the models predict 94L will take a significant northward jog 3 - 5 days from now, in response to a strong trough of low pressure passing to the north (this is the same trough of low pressure that will be recurving Danny out to sea). It is then probable that 94L will be forced to the west again as the high pressure ridge steering the storm builds back in, and 94L will likely be a few hundred miles northeast of the Northern Lesser Antilles Islands seven days from now.

I'll have an update this afternoon.

Jeff Masters

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ref-357) The outerbanks and residence can weather 50 knots ir the tourists can be evacuated. Depending upon the tides there may be some overwash but that is a hardy group on that sand.
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372. AndyN
Quoting Funkadelic:


Actually that wave could be a future problem, it is far south and models are picking up on it. The reason why I call this wave a problem is due to the fact that by the time this feautre gets close to the islands; the high will be back in place and steering it mainly west/wnw. So by Monday morning we will see tropical depression and 95L.


Are you referring to storm currently over Africa?
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Quoting yonzabam:


Just googled it. Tropical storm Christine was a depression with winds of 35 mph before it left Africa in 1973, making it the easternmost tropical depression on record, so just short of being a named storm.


I stand corrected; 11N14W winds at 35mph...definitely on the African continent (but only just)
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ORCA,

I think I see my house!
Member Since: August 22, 2006 Posts: 0 Comments: 1449
I "got a feelin" 94L is gonna be an east coast surfer too
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CAF wave view updates every 15 minutes.
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366. bwat
Tropical Storm Christine(1973), formed at around 14w as a depression.
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365. 7544
if he stays staionary wouldnt the high build in and push him further west and maybe abit south west could he be tying to pull a jean
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Quoting Seastep:
Will remain TS Danny, unless that's the only wind they find.

29.117N 74.617W

37 knots
(~ 42.5 mph)


Yeah. The winds are still TS strength it appears away from the center. Just funny though...that within 50-100 miles of the center there is barely any wind.
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Quoting surfsidesindy:
So in order for it to be a TD when it exits Africa it would have to have a LLC and 38mph winds? I was watching this yesterday and decided to wait until today to comment on it, just to see if it held together. It looks just about the same, if not larger and more symmetrical than yesterday.


Well it would need to persist over water for about 24 hours and have a LLC with winds of 30mph. But I doubt it'll develop that quickly once it exits.
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Quoting nolacane2009:
Boy this site is really slow today. I remember yesterday it was hard to keep up with the entries.
Maybe some people are in school.
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360. AndyN
Good view of large storm over Central Africa coming into frame:



Link
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Quoting cdnbananabelt:


Stormchaser, is it far south enough to not be intruded by SAL? What's your take on it?


I haven't put much time into looking at the future conditions, but I would imagine that SAL wouldnt increase all that much between now and the period when it exits. Looking at some loops of the wave broad cyclonic turning is already noticeable. I havent seen a wave this good since last year. I imagine if it can keep its presentation it should become an invest once it hits the water.
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Quoting Parakeyt:
to cdnabananabelt: That's a great link,very helpful to me as a newbie and learning


I'm a bit of a newbie myself - but this is a great place for learning. I've followed a lot of links too - for the most part, they're awesome tools. :)
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Using Google Earth.. this area looks like it has a ton of people living on it.. how well can it handle a 50 kt wind and surge?



Even if Danny keeps goes straight North, and quits this west stuff... they are going to get smacked.

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Boy this site is really slow today. I remember yesterday it was hard to keep up with the entries.
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Quoting Floodman:


I've seen them become invests as soon as they hit the water...there are things said in here sometimes that are, well, to be mild, inaccurate...


Just googled it. Tropical storm Christine was a depression with winds of 35 mph before it left Africa in 1973, making it the easternmost tropical depression on record, so just short of being a named storm.
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So in order for it to be a TD when it exits Africa it would have to have a LLC and 38mph winds? I was watching this yesterday and decided to wait until today to comment on it, just to see if it held together. It looks just about the same, if not larger and more symmetrical than yesterday.
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Will remain TS Danny, unless that's the only wind they find.

29.117N 74.617W

37 knots
(~ 42.5 mph)
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Was it expected for Danny to stall again? I am wondering why it is stalling? Is it going to make that northerly turn that has been anticipated for so long or go west?
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Quoting Stormchaser2007:
This central African wave is a beast. It already shows signs of a MLC. Should be interesting to see what happens when it exits this weekend.



Stormchaser, is it far south enough to not be intruded by SAL? What's your take on it?
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Quoting Orcasystems:
I personally think they have NFI where the centre of Danny is.. or if it even has one?



With decent circulation, the HH flags point directly to the center of circulation. Just take a line that's perpendicular to the flags. Where the lines from multiple flags intersect is the center of circulation.

When the circulation is well defined, such an intersection will be the same no matter which flags you choose. Doing that for the current flight, I get a position of 30° 4'52.58"N, 75°41'6.11"W, which is west of where the red path cone is, but pretty close to the dropsonde.
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TD Danny.
Member Since: August 22, 2006 Posts: 0 Comments: 1449
348. Asta
Hey All-

I think that Danny will sit and sit and spin and then go west... It's going to folow the SST lines.. sounds crazy I know- but its blocked by the Temps..
wants to go west.. just watch- it may dip south west first before going west if I am correct..
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Found 39mph not too far S of the center, though at 29.600N 75.133W. If I'm remembering, they were only finding higher winds to the N and E before, and far removed from the center. Please correct me if that is inaccurate.

Modified to add "and far removed from the center"
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to cdnabananabelt: That's a great link,very helpful to me as a newbie and learning
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Quoting yonzabam:


I believe one has been named before it emerged from Africa.


that rings a bell with me, too...
Member Since: August 13, 2007 Posts: 0 Comments: 10458
danny reminds me of one of my kids, never wants to stay in one place..
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Vortex Message from Hurricane Hunters from 1:50PM EDT appears below.

Center is in the naked CoC. Definitely a warm core storm - finally a slight rise in temp near the center. Winds are extremely weak though near the center - Max out at 17 knots.




Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 28th day of the month at 17:50Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 302)
Storm Number & Year: 05L in 2009
Storm Name: Danny (flight originating in the North Atlantic basin)
Mission Number: 8
Observation Number: 05
A. Time of Center Fix: 28th day of the month at 17:31:40Z
B. Center Fix Coordinates: 30°04'N 75°42'W (30.0667N 75.7W)
B. Center Fix Location: 313 miles (504 km) to the SE (143°) from Myrtle Beach, SC, USA.
C. Minimum Height at Standard Level: Not Available
D. Estimated (by SFMR or visually) Maximum Surface Wind: 26kts (~ 29.9mph)
E. Location of the Estimated Maximum Surface Wind: 63 nautical miles (72 statute miles) to the NW (311°) of center fix
F. Maximum Flight Level Wind Inbound: From 47° at 17kts (From the NE at ~ 19.6mph)
G. Location of Maximum Flight Level Wind Inbound: 26 nautical miles (30 statute miles) to the NW (312°) of center fix
H. Minimum Sea Level Pressure: 1007mb (29.74 inHg) - Extrapolated
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 23°C (73°F) at a pressure alt. of 457m (1,499ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 25°C (77°F) at a pressure alt. of 455m (1,493ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 22°C (72°F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Not Available
M. Eye Shape: Not Available
N. Fix Determined By: Penetration, Radar, Wind, Pressure and Temperature
N. Fix Levels (sfc and flt lvl centers are within 5nm of each other): Surface and 1,500 feet
O. Navigation Fix Accuracy: 0.02 nautical miles
O. Meteorological Accuracy: 1 nautical mile
Remarks Section - Remarks That Were Decoded...
Maximum Flight Level Wind: 17kts (~ 19.6mph) in the northwest quadrant at 17:23:00Z
Remarks Section - Additional Remarks...
SLP EXTRAP FROM BELOW 1500 FT
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This central African wave is a beast. It already shows signs of a MLC. Should be interesting to see what happens when it exits this weekend.

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Its even further west then they thought.

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Wow, Danny has been the most unpredictable storm of the last few years. Reminds of Hannah.
Member Since: August 22, 2006 Posts: 0 Comments: 1449
95C is looking better than it ever did
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Quoting yonzabam:


Well, I read it on here a few days back. Could be wrong, though.


I've seen them become invests as soon as they hit the water...there are things said in here sometimes that are, well, to be mild, inaccurate...
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Danny seems to be doing what he wants to do.He's stationary when he is not suppose to be(as of the 2pm advisory)he's in a whole world onto himself LOL.No I'll go west,no I'll go north,maybe stand still.He'll really throw the guidance off if he is still barely moving at the 8pm advisory.
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Quoting Floodman:


To the best of my knowledge, that is incorrect...Thunderstorm Felix?


Well, I read it on here a few days back. Could be wrong, though.
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Quoting jaxbeachbum:
Should have worded that question different. At what point will Danny get into the jet stream? I think you may be a lil confused the jet stream is upper level wind. The gulf stream is water
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Looking at the Washington Edu WV loop it appears the low south of the big cigar is trying to pull from all sides and create the storm of the century.By the way does anyone know the actual time or delay on the washington WV loop?
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330. JLPR
that TW inland in Africa is sure looking Good right now

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Quoting bwat:
I'm no expert but I don't think the jet stream is going to have an effect of the steering of Danny. I believe he is being steered by an approching trough to the west and high pressure in the east. If I am telling you wrong I'm sure someone will correct me.


You are correct...typically the jet stream has little or nothing to with tropical systems over water other it's effect on features that would potentially effect the tropical system, if that makes sense
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328. bwat
Quoting jaxbeachbum:
Should have worded that question different. At what point will Danny get into the jet stream?

I'm no expert but I don't think the jet stream is going to have an effect of the steering of Danny. I believe he is being steered by an approching trough to the west and high pressure in the east. If I am telling you wrong I'm sure someone will correct me.
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327. JRRP
i think GFDL and HWRF will show 94L toward the carib
Member Since: August 16, 2007 Posts: 0 Comments: 5085
Slight strengthening from last advisory and now stationary.

...SUMMARY OF 200 PM EDT INFORMATION...
LOCATION...30.1N 75.7W
MAXIMUM SUSTAINED WINDS...40 MPH
PRESENT MOVEMENT...STATIONARY
MINIMUM CENTRAL PRESSURE...1007 MB
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Quoting yonzabam:


I believe one has been named before it emerged from Africa.


To the best of my knowledge, that is incorrect...Thunderstorm Felix?
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Link
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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.