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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Quoting StSimonsIslandGAGuy:
Does anyone have a link showing the low level BAM track for Danny?


You can select just the BAMS here
Member Since: September 23, 2005 Posts: 14 Comments: 10876
man this season so far is something else..Florida seems to have a purchased a deflector shield program.. everytime a system looks like it may or could develop. A east coast trof shows up. or if it lifts .it splits and leaves an upper low..same with 94L as it starts to develop an upper low looks to develop in the face of the ridge lifting more it N.. even if this does't happen another STRONG east coast trof tries to show up in 10 days or so..
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And 18 Z, but much harder to pick out individual BAM flavors:


(Click for full size)
Member Since: August 16, 2007 Posts: 6 Comments: 12461
I am sure glad I am not a MET... I would be looking at where I think Danny is going... and I would look at where I thought he had been...and where he has actually been...and assume I was making a big mistake somehow. I wonder if the GIGO principle is seriously being over looked?


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Guys we really don't know what the actual pattern will be in September. People need to stop being overly confident. I understand you want no storms, I don't either, but we can't just call the season a 2006 season just yet. Who knows, maybe a Hurricane will come knocking on your door.
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Quoting Drakoen:
94L is slowly becoming better organized. The system has a broad low level circulation within the ITCZ. The 200mb observations indicate an upper level anticyclone over head which should aid in development. The system's environment is steadily becoming more moist.
Would you put it at 11N?
Member Since: August 10, 2007 Posts: 0 Comments: 3224
Quoting Patrap:

Looks stationary and naked!
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Quoting btwntx08:

what western shear the model overreacting outlier throw is model away from now


An elongated trough is expected to increase upper level winds to its northwest. The GFS expects the retrograde far enough for it not be impacted by the shear, but the ECMWF expects this upper trough to linger.
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Quoting NEwxguy:
a lot of people must have taken friday off,the people in this blog today are actually polite to each other,I like this


With a couple of notable exceptions, but yes, this is more like it once was...or am I looking at the past through rose-coloured glasses?
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Quoting StSimonsIslandGAGuy:
Does anyone have a link showing the low level BAM track for Danny?

Not BAMS by itself, the red is easy to pick out here (is from 12 Z):


(Click for full size)
Member Since: August 16, 2007 Posts: 6 Comments: 12461
Quoting Drakoen:
94L is slowly becoming better organized. The system has a broad low level circulation within the ITCZ. The 200mb observations indicate an upper level anticyclone over head which should aid in development. The system's environment is steadily becoming more moist.


Drak did you see JAWS on the 12z ECMWF? Nothing will get past the huge trof.
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94L is slowly becoming better organized. The system has a broad low level circulation within the ITCZ. The 200mb observations indicate an upper level anticyclone over head which should aid in development. The system's environment is steadily becoming more moist.
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OSUWXGUY

You were right, no other LLC. Recon just went through the area I thought they might find one, no wind shifts.
Member Since: September 23, 2005 Posts: 14 Comments: 10876
Quoting nrtiwlnvragn:


I'm doing good, thanks for asking.


Outstanding!
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Quoting Patrap:


Looks like it's finally starting to move in response to the approaching system.
Member Since: May 27, 2008 Posts: 0 Comments: 419
Quoting btwntx08:

what western shear the model overreacting outlier throw is model away from now


Huh?
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Is Danny moving or still stationary????
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Quoting hurricane23:


Pattern change? Thats one massive trof of low pressure of the eastcoast on this 12z ecmwf.Nothing will break through that.


There are some variations here and there, but there will likely be troughing over the east coast. Notice the troughing pattern setting up over the west coast Adrian. The 500mb ensemble mean are still expecting the pattern to change.

I still think it will change by september 10th.

let's just wait and see bud :)
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Quoting katroy:
The 2:00 NHC advisory indicates the next Danny advisory will be posted at 5:00, but that Hurricane Hunter aircraft is currently investigating the storm. Are they likely to post an interim advisory before 5:00 if the data indicates he has weakened to a depression? I need to do an internal update (preferably before 5:00 EDT) and would really like to be able say it's been downgraded. Thanks!


No, only special advisories are issued to upgrade systems (ex. from a TS to a hurricane, or like a cat 1 hurricane to a cat 4
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497. hamla
way back on blog entry 171
i said wat if danny boy stops and i come back now and at 2pm nhc update it said it has been stationary and will remain so for a few hours
if the blob on the east side catches up all bets off
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Quoting katroy:
The 2:00 NHC advisory indicates the next Danny advisory will be posted at 5:00, but that Hurricane Hunter aircraft is currently investigating the storm. Are they likely to post an interim advisory before 5:00 if the data indicates he has weakened to a depression? I need to do an internal update (preferably before 5:00 EDT) and would really like to be able say it's been downgraded. Thanks!


They will wait until 5pm. But, sometimes the 5pm comes out earlier than 5pm.

Watch this blog...I subscribe to a program for getting the updates quickly, and I can't beat these guys when it comes to posting it here.
Member Since: May 27, 2008 Posts: 0 Comments: 419



GFDL and HWRF were not run on 94L at 12Z.
Member Since: September 23, 2005 Posts: 14 Comments: 10876
danny looks really sheared...about gone to me.
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Quoting Floodman:


Oh, you mean JFVWS?
oh no its 3:00 schools out and that means comedy hour is about to start!!
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Quoting futuremet:
12Z ECMWF dissipates 94L due to westerly shear.


Pattern change? Thats one massive trof of low pressure of the eastcoast on this 12z ecmwf.Nothing will break through that.
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a lot of people must have taken friday off,the people in this blog today are actually polite to each other,I like this
Member Since: September 6, 2007 Posts: 874 Comments: 15595
Quoting MBwxwatcher:
Well local mets said absolutly no rain from danny and here in myrtle beach we have gotten almost an inch just in the afternoon all coming off the ocean


They are probably correct. It looks liek the rain you are getting is actually part of a frontal boundry moving through your area from the west and not directly from Danny.
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Quoting Snakemaster:
Whatever happened to hurricaine Erkel?


Oh, you mean JFVWS?
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Quoting Floodman:


Thanks! How have you been by the way? Haven't been in very much and it's good to see the same faces in here...


I'm doing good, thanks for asking.
Member Since: September 23, 2005 Posts: 14 Comments: 10876
12z ECMWF -

ECMWF
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The 2:00 NHC advisory indicates the next Danny advisory will be posted at 5:00, but that Hurricane Hunter aircraft is currently investigating the storm. Are they likely to post an interim advisory before 5:00 if the data indicates he has weakened to a depression? I need to do an internal update (preferably before 5:00 EDT) and would really like to be able say it's been downgraded. Thanks!
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don't see any kind of circulation at 11N..some of the modeling with 94L is really odd...
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Quoting nrtiwlnvragn:


EUMETSAT


Thanks! How have you been by the way? Haven't been in very much and it's good to see the same faces in here...
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The clash of two systems.

Link

Member Since: May 27, 2008 Posts: 0 Comments: 419
Is 94L really at 11N?
Member Since: August 10, 2007 Posts: 0 Comments: 3224
one of my favorite animations of the atlantic basin, if im not mistaken got this from tampaspin site..btw you can see the LLC on 94L clearly.

Link
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Surely someone from chicago
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Quoting tornadodude:


or you can continue to ask people on here, the majority of us don't mind answering questions, we are usually glad to help


Sweet,
Hey do you know what time it is?
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Sorry for the delay in response. My computer or the blog or both is SLOW. Hello, Presslord. I've got the history channel 1938 storm program on in the background now. It's excellent. Hope you are well.
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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.