Danny disorganized, but generating strong winds

By: Dr. Jeff Masters , 1:55 PM GMT on August 27, 2009

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Tropical Storm Danny continues to look disorganized this morning. The low level circulation center is exposed to view, with the heaviest thunderstorms lying several hundred miles east of the center. The center has undergone several relocations over the past 12 hours, and may do so yet again this morning, in order to position itself nearer to the heaviest thunderstorm activity. Despite its disorganization, Danny continues to generate strong winds, with the Hurricane Hunters and QuikSCAT both reporting winds in the 55 - 60 mph range early this morning. There is plenty of dry air in Danny's vicinity interfering with development, thanks to an upper-level trough of low pressure.


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 intensity forecast for Danny
The upper-level low that has been keeping Danny disorganized has weakened and separated from the storm, leaving Danny in a region with moderate wind shear of 10 - 15 knots and a modest amount of dry air. These environmental conditions will remain roughly constant through Friday night. Slow to moderate strengthening of Danny to a Category 1 hurricane should result, and is called for by all of the reliable intensity models. By Friday night, a trough of low pressure will approach the U.S. East Coast and bring high wind shear of 20 - 35 knots through Saturday. Danny will be close enough to this trough that the trough may be able to feed energy to Danny as the trough converts Danny to an extratropical storm. As a result, Danny may not weaken as fast as one might ordinarily expect, given the high levels of wind shear expected on Saturday. A landfall in Cape Cod, eastern Maine, or Nova Scotia with 55 - 75 mph winds is a good bet.


Figure 2. Performance of the main models used to forecast Hurricane Bill. Forecasts for the time periods 24, 48, 72, 96, and 120 hours are shown, with the track errors for each models' forecasts in nautical miles (nm). The statistics are shown for the regular interpolated version of the models used by the NHC forecasters in real time to make their forecasts. The "Consensus" model is the NHC's TVCN consensus, which is the average of at least two of the other models shown here (but not including the Canadian model). The Canadian model had the best performance of any model for Bill, surpassing even the Official NHC forecast. The next best performing models were the GFDL and GFS. Last year's best performing model, the European Center model, was not available for this analysis. Image credit: Dr. Jim Goerss, Navy Research Lab, Monterey.

The track forecast for Danny
Wunderground provides a computer models plot showing the hurricane track forecasts of most of the major models used by NHC to formulate their official forecast (one notable exception: we can't show the European Center ECMWF model, since this model is not freely available). One of the most frequently asked questions I get is, "which model do you trust?" This morning we have several models like the NOGAPS and Canadian calling for Danny to pass very near Cape Hatteras, North Carolina, then over Cape Cod, Massachusetts. The rest of the models foresee Danny missing Cape Hatteras, and continuing on to an encounter with Nova Scotia instead of Cape Cod. According the 2008 NHC forecast verification report, the best performing model during the 2008 hurricane season was the European Model (ECMWF), by a wide margin. The ECMWF out-performed the official NHC forecast, and it is very rare for an individual model to do this. The next best models were the GFDL and HWRF, while the NOGAPS, UKMET, and GFDN did the worst of the major models. The Canadian model was not analyzed, but historically has been among the worst of the models for forecasting hurricanes.

So far this year, the ECMWF has also done well. Unfortunately, the European Center group does not make the output of their hurricane tracking module publicly available, so I cannot present any statistics of their model's performance. Somewhat surprisingly, the Canadian model has also done very well this year. The model received a major upgrade in its physics of the past year, and has performed extremely well in hurricane track forecasts for both the Eastern Pacific and the Atlantic so far this year. In fact, for Hurricane Bill, the Canadian model gave better track forecasts then the NHC did (Figure 2). Danny is a different storm than Bill, and it is possible that the Canadian model will do less well with a storm that is disorganized, like Danny is. Nevertheless, with the Canadian model consistently keeping a Danny's track close to Cape Hatteras and going over southeastern Massachusetts, residents of these areas need to be prepared for possible hurricane conditions from Danny. Given the recent reformation of Danny's center, and the possibility of yet another reformation later today, all of the track models must be viewed with more than the usual amount of doubt. Since the center reformations have been moving Danny's center to the north and east, it may be that the Canadian model's prediction lies too close to the U.S. coast.

For those of you wondering about specific probabilities of getting tropical storm force or hurricane force winds, consult the NHC Wind Probability Product. The 11 am EDT NHC forecast gave Cape Hatteras a 4% chance of seeing hurricane force winds from Danny, and Nantucket, MA, a 7% chance.

For more information on computer models used by NHC
Basics of hurricane forecast models (Dr. Jeff Masters, wunderground.com, updated 2007)
Description of computer models used for hurricane forecasts (NHC, updated 2009)
Description of computer models used for hurricane forecasts (NOAA/AOML)


Figure 3. Tropical wave 94L off the coast of Africa.

Invest 94L off the coast of Africa
A well-organized tropical wave lies a few hundred miles southwest of the Cape Verdes Islands, near the coast of Africa. This wave was designated 94L by NHC this morning. Shear is low, about 10 knots, and waters are warm enough to support development. The dry Saharan Air Layer is relatively limited in extent and intensity, so dry air may have only a small inhibiting effect on the wave. Expect some slow development of this wave as it moves westward over the next few days. NHC is giving this system a low (less than 30% chance) of developing into a tropical depression by Saturday. This system is moving rather slowly, 10 - 15 mph, and it will be at least a week before it approaches the Lesser Antilles Islands. The GFS model develops 94L into a tropical depression early next week.

Special note on using the Canadian model
While the Canadian model has been doing well with hurricane track forecasts this year, the model still does a poor job forecasting the genesis of new tropical cyclones. The Canadian model has a false alarm rate perhaps three times higher than any other model, so one should not believe the Canadian model's regular predictions of new tropical cyclones springing up. You can access output from the Canadian model at Environment Canada or at Florida State University or Penn State.

I'll have an update later today.

Jeff Masters

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Quoting KEHCharleston:
542. DoubleBranchGuy
; ) Bless your heart.
If I may add. You are either from Charleston or you are from 'off'. Doesn't matter whether it is Colombia, South American or Columbia, SC.


yup KEH...DoubleBranch gets it...looks like bad lookin weather comin to us goin over the Stono Bridge onto Johns Island...
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562. IKE
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
200 PM EDT THU AUG 27 2009

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON TROPICAL
STORM DANNY...LOCATED ABOUT 550 MILES SOUTH-SOUTHEAST OF CAPE
HATTERAS NORTH CAROLINA.

A TROPICAL WAVE IS LOCATED OVER THE FAR EASTERN ATLANTIC OCEAN ABOUT
350 MILES SOUTH-SOUTHWEST OF THE CAPE VERDE ISLANDS. THE ASSOCIATED
SHOWER ACTIVITY CONTINUES TO SHOW SIGNS OF ORGANIZATION
...AND SLOW
DEVELOPMENT OF THIS SYSTEM IS POSSIBLE OVER THE NEXT COUPLE OF DAYS
AS IT MOVES WESTWARD AT 10 TO 15 MPH. THERE IS A MEDIUM CHANCE...
30 TO 50 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE
DURING THE NEXT 48 HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
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come on 94L
you look like a good fishy fishy fishy...
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Shouldn't really read too much in to the models for 94L - it hasn't even deserved an orange circle from NHC yet... LOL!

All I can tell is that it's moving WEST for now...
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Quoting coffeecrusader:
According to the gfs and hwrf, 94l will become a fish storm. 2009 is the year of the fish storm. Too mant troughs. Also high shear in the GOM this season. Looks like Florida and points west are in the clear this year.


thats a really bold statement
Member Since: June 28, 2006 Posts: 25 Comments: 8326
12Z HWRF turns 94L northward in the CATL, but it is currently located around 10N and this may be too far south for such a northerly component.
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According to the gfs and hwrf, 94l will become a fish storm. 2009 is the year of the fish storm. Too mant troughs. Also high shear in the GOM this season. Looks like Florida and points west are in the clear this year.
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Good afternoon, all! Wow, I'm really confusing in tropical storm form...two apparent centers moving in two different directions; not expected to strengthen to hurricane strength until I'm extra-tropical...sorry about all that. :(
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Member Since: September 14, 2007 Posts: 3 Comments: 3963
Quoting F5Tornado:
Looks like Danny is dissapating.. the exposed Center, shear, and also, dry air look like they are all going to stop Danny from becoming A Hurricane. Like I said in the last JeffMasters blog, I think that we could be dealing with a depression by tonight. Sorry, I said tomorrow night last night! IT was 4:00 a.m. in the morning, and my brain was BBQed enough to make ShishKebab (yuck) and I kind of was drowsy. I meant Tonight.

Take a look at the wind shear!
http://cimss.ssec.wisc.edu/tropic2/real-time/atlantic/winds/wg8sht.GIF
http://cimss.ssec.wisc.edu/tropic2/real-time/atlantic/winds/wg8shr.GIF

Looks strong enough to hurt Danny a little more, especialy if you imply dry air!

Whats your opinion guys?


i think it is reforming farther east, but jmo. doesnt get listened to very often either :P
Member Since: June 28, 2006 Posts: 25 Comments: 8326
Quoting IKE:
12Z HWRF on 94L....

Is the HWRF showing 94L as a fish storm?
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542. DoubleBranchGuy
; ) Bless your heart.
If I may add. You are either from Charleston or you are from 'off'. Doesn't matter whether it is Colombia, South American or Columbia, SC.
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commenting on bill........i was on daytona beach all last week for vacation and i've, never in my life, felt such powerful waves/undertow. you could literally be standing in knee deep water, plop down on your stomach and the water would just carry you for yards from south to north along the beach. then a wave would come along and slap you right back on your feet. amazing....
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Looks like Danny is dissapating.. the exposed Center, shear, and also, dry air look like they are all going to stop Danny from becoming A Hurricane. Like I said in the last JeffMasters blog, I think that we could be dealing with a depression by tonight. Sorry, I said tomorrow night last night! IT was 4:00 a.m. in the morning, and my brain was BBQed enough to make ShishKebab (yuck) and I kind of was drowsy. I meant Tonight.

Take a look at the wind shear!
http://cimss.ssec.wisc.edu/tropic2/real-time/atlantic/winds/wg8sht.GIF
http://cimss.ssec.wisc.edu/tropic2/real-time/atlantic/winds/wg8shr.GIF

Looks strong enough to hurt Danny a little more, especialy if you imply dry air!

Whats your opinion guys?
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Quoting presslord:


feel free to ignore...in fact, I'd be honored if you did...

Sweet. :) No local pride (and I'm six miles from the border).
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Looks like Danny's making a run to restructure himself.
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544. IKE
Quoting Dakster:
IKE - I just love that HWRF track for 94L.. Chances of it going that way?



Shows a weakness out in the EATL. I guess it's possible. Then shows high pressure building back in forcing it back more to the west. Seems to have some model support. See what happens.
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Member Since: September 14, 2007 Posts: 3 Comments: 3963
As a 7th generaton North Carolinian, I understand where this is coming from...especially those from South Carolina, who have a sometimes secret/sometimes not so secret loathing of North Carolina. However, as a BBQ man, our "Carolina" culture is quite clearly broken into three completely different sections...Western North Carolina...Eastern North Carolina...and South Carolina...None of them like each other much, and if you include football, then you break it into 4 cultures and divide South Carolina up into Clemson vs. South Carolina. Those people are SERIOUS about distinctions. It's a wonderful place to live, but you got to know who is what, and what means what...lol...Me? Having my long time home in North Carolina, and my long time beach home in South Carolina, I'm a fence straddler. I love ALL of it, especially the BBQ, which is incredible from all sections...and if you've never had South Carolina mustard-based BBQ, you are missing out on one of life's great treats. BUT, when "Pressed", I will lay it out as Go Panthers, Go Wolfpack, Go Gamecocks and Go Lexington Style BBQ. The "Carolina's" are a complicated piece of work...lol...but one extra point, I'm pretty sure those that do not know all these things use that phrase the same way you guys use "Conus", "GOM" etc. It's just a shortening of words. If you condensed THEIR state though, such as "Alabama...Auburn...what's the difference?"...you would for SURE hear about...lol...ok...back to lurking and learning...
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Quoting KEHCharleston:

????
Ok... 'Buy Local' is my bandwagon! Saves energy, promotes the local economy etc.
On my blog, I have listed products made in the Americas - plural. It is not about USA goods vs. Canadian goods vs Trinidad & Tobago goods. It is about buying local, and if you can't buy local buy from your friends.

Don't do drugs - do not eat imported shrimp


Too late :-)
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Question?

I saw on the blog this morning that someone said the NHC updates were hours in the making, so will the 2:00 update reflect what the HH find?
Member Since: August 19, 2006 Posts: 13 Comments: 15282
Quoting OSUWXGUY:
Back from lunch and boy do I have a lot to say...


First off, in regards to the question of lightning and hurricanes:


Within a typical thunderstorm over land, area of strong updrafts and strong downdrafts are small and are in close proximity. Ice particles within the storm bumb into each other, leading to charge separation and the upper portions of a storm becomes a different polarity than the lower portions of the cloud. Lightning then occurs either within the cloud or between the cloud and the ground based on the charges built up.


Within a hurricane, regions of strong updrafts and strong downdraft are much larger in size. Alternating large regions of the storm (eyewall for instance) head upward and downward.

The fact that these regions ARE so broad is what allow hurricane hunters to fly into intense hurricane. Airplanes cannot safely fly into the core of intense thunderstorms and try to avoid this whenever possible...

The broader areas of updrafts and downdrafts leads to less ice particle collision and preferential separation within a hurricane. No charge separation = no lightning.

Now in the rain bands in the periphery of the hurricane, individual storms have the charateristics that allow lightning to form - and is why folks have reported seeing lightning with rainbands but not usually with the hurricane itself.


One final note to complicate things... Sometime within the hurricane, small areas of very strong rotation (mesocyclones) can form causing supercell like structures to rotate around the eye or inner structure of the storm. These areas cause localized (small) areas of intense vertical motion - more like a normal thundestorm over land - and can cause lightning!
Cross Section of a Hurricane


Thx OSU...
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Quoting TampaSpin:


You don't have that type of sence of humor......LOL....sorta like buying American and not Canadaian!.....ROFLMAO

????
Ok... Now you are stepping on my soap box.
'Buy Local' saves energy, promotes the local economy etc.
On my blog, I have listed products made in the Americas - plural. Not just USA goods, It is not USA vs. Canada vs Trinidad & Tobago. It is about buying local, supporting your local economy - and if you can't buy local, then buy from your friends.

Don't do drugs - do not eat imported shrimp
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what is with the white tube like clouds surrounding the convection? link
Member Since: June 28, 2006 Posts: 25 Comments: 8326
Quoting IKE:
12Z HWRF on 94L....


That turn to the north would be nice.
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1 COC @71deg 1 COC@73.3 both @27.5N

sound right?
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IKE - I just love that HWRF track for 94L.. Chances of it going that way?

Member Since: March 10, 2006 Posts: 0 Comments: 10264
Not sure which they want to plot from, but this storm is tilted way to the right. The center still is not stacking up to any degree. In fact the LLC is actually moving W with some southern movement. However, the ULC or what appears to be it, looks to have stalled or moved a bit north. So I'm starting to wonder if the LLC has been ejected and there is a new LLC forming under the deepest storms. If you look at some of the last frames of the visible sat there's a change in direction of the lower clouds instead of the steady march towards the LLC they seem to have stopped and started moving north under the bigger storms.
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530. IKE
12Z HWRF on 94L....
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Quoting presslord:
anyone who doesn't get that I'm pokin' fun at MYSELF hasn't been payin' attention...


dont sweat it Press
we know ya love the carolinas LOL
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Quoting TheCaneWhisperer:
One other thing to chomp on. Highest winds (Stronger Circulation) were in the lower levels. Could it be that as conditions improve your looking at a better defined MLC of an unstacked system. What level were the HH flying when they caught the new wind shift?


about 25,000ft
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Quoting groundswell:
SYNOPSIS FOR FLAGLER BEACH TO JUPITER INLET OUT 60 NM-
1029 AM EDT THU AUG 27 2009

SYNOPSIS
TROPICAL STORM DANNY WILL REMAIN WELL EAST OF THE FLORIDA
COASTAL WATERS AS IT RECURVES AND MOVES UP THE EASTERN SEABOARD.
SWELLS GENERATED BY DANNY WILL IMPACT THE LOCAL WATERS THROUGH
FRIDAY. REFER TO THE LATEST ADVISORIES FROM THE NATIONAL HURRICANE
CENTER CONCERNING DANNY. A LIGHT SOUTH TO SOUTHWEST WIND FLOW WILL
DEVELOP BY THE WEEKEND AS THE ATLANTIC HIGH PRESSURE RIDGE AXIS
SHIFTS SOUTH OF THE AREA.

Actually, swells will be present through Sunday, the more west it goes, the bigger and longer it will be. And if it intensifies, could be another major swell event. But Danny is no Bill, Bill was a once in ten year event for Florida.


I don't know about that...what about Bertha last year?? Her swells and waves were bigger here in Central FL than Bills were.
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Quoting presslord:
anyone who doesn't get that I'm pokin' fun at MYSELF hasn't been payin' attention...


I got it... Back to the no one gets sarcasm anymore...

NHC says Danny is moving NW because that is way the see it. They stated it was going due west at 310 degrees, which is NOT DUE WEST.

Anyways, I have faith that they will change the cone of death and destruction when and IF warranted.
Member Since: March 10, 2006 Posts: 0 Comments: 10264
good afternoon all,

looks danny is in a tired of the beating from the sheer, not moving yet..
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Quoting btwntx08:
94L still looking good


Yes it does, and as soon as we get rid of ole Danny Boy, I will turn my attention to that west-tracker. Hope there are more troughs in the east coasts' near future.
Member Since: June 29, 2007 Posts: 0 Comments: 1136
hey press i'm in myrtle beach,are we safe
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1 COC @71deg 1 COC@73.3 both @27.5N
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Quoting presslord:
anyone who doesn't get that I'm pokin' fun at MYSELF hasn't been payin' attention...


You don't have that type of sence of humor......LOL....sorta like buying American and not Canadaian!.....ROFLMAO
Member Since: September 2, 2007 Posts: 178 Comments: 20439
Looks like the old COC is weakening and being replaced by one due east...
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That could also be causing the stall as Danny try's to pull himself together.
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There is no New LLC to the east... its just Thunderstorms building south along feeder bands with shearing cloud tops blowing to the east..

Danny is stuck between ridges and upper lows.....eventually the upper low to its west will start to pull Danny NNW later this evening... then north on Friday nearing the outerbanks by later in the day!

There still is cold air in this system..and it wont be totally tropical all the way to N.E... more of a Nor-easter.. still Hurricane watches will probably go up for the caronlinas this evening or tonight @ 11pm and for N.E. on Friday!
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SYNOPSIS FOR FLAGLER BEACH TO JUPITER INLET OUT 60 NM-
1029 AM EDT THU AUG 27 2009

SYNOPSIS
TROPICAL STORM DANNY WILL REMAIN WELL EAST OF THE FLORIDA
COASTAL WATERS AS IT RECURVES AND MOVES UP THE EASTERN SEABOARD.
SWELLS GENERATED BY DANNY WILL IMPACT THE LOCAL WATERS THROUGH
FRIDAY. REFER TO THE LATEST ADVISORIES FROM THE NATIONAL HURRICANE
CENTER CONCERNING DANNY. A LIGHT SOUTH TO SOUTHWEST WIND FLOW WILL
DEVELOP BY THE WEEKEND AS THE ATLANTIC HIGH PRESSURE RIDGE AXIS
SHIFTS SOUTH OF THE AREA.

Actually, swells will be present through Sunday, the more west it goes, the bigger and longer it will be. And if it intensifies, could be another major swell event. But Danny is no Bill, Bill was a once in ten year event for Florida.
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Were having some squally weather here in Mobile AL.
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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.