Danielle a hurricane; TD 7 forming off coast of Africa

By: Dr. Jeff Masters , 2:18 PM GMT on August 24, 2010

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Hurricane Danielle has stopped intensifying and is now looking a bit ragged this morning, but remains a respectable Category 1 hurricane with 80 mph winds. The intensity of Danielle's heavy thunderstorms has waned in the past few hours, and the organization of the storm is less impressive. This is probably due do strong upper-level winds out of the west that are creating a moderate 10 - 20 knots of wind shear, and injecting some of the dry air from the Saharan Air Layer (SAL) that surrounds Danielle. Danielle is over warm 28°C water, but is far from any land areas.


Figure 1. Morning satellite image of Tropical Storm Danielle (left side of image) and the forming Tropical Depression Seven (right side of image.)

Forecast for Danielle
A powerful trough of low pressure over the mid-Atlantic Ocean will begin to pull Danielle more to the northwest by Wednesday, keeping Danielle well to the east of Bermuda. Most of the models predict that this trough will be strong enough to fully recurve Danielle out to sea. It is possible that Danielle could eventually threaten Newfoundland, Canada, but it currently does not appear that any other land areas will be at risk from this storm. History suggests that a storm in Danielle's current location has only a 20% chance of making landfall on the U.S. East Coast. If Danielle passes east of Bermuda, as forecast, these percentages drop to less than 5%. As far as intensity goes, it is looking unlikely that Danielle will attain major hurricane status (115+ mph winds.) There is enough dry air and wind shear affecting the storm today that it will take several days for the storm to recover its strength, making it less likely the storm can hit Category 3.

The formation of Danielle is remarkable in this it was successfully forecast by the GFS model nearly two weeks in advance. The ECMWF and NOGAPS models also did a good job of predicting Danielle's formation a week in advance. The models are getting better and better each year at forecasting genesis of tropical cyclones, though a successful 1-week forecast of genesis is still a rarity. For example, none of the models foresaw the development of 96L until just 3 - 4 days ago.


Figure 2. Plot showing historically the percent chance of a tropical cyclone in a given location impacting the U.S. East Coast. For storms in Danielle's current position (orange hurricane symbol), about 20% of them go on to hit the U.S. East Coast. For storms in 96L's current location (red circle with a "?" in it), the odds are also 20%. Image credit: Bob Hart, Florida State University.

96L (soon to be Tropical Depression Seven)
Satellite images suggests that a tropical wave (96L) that emerged off the coast of Africa yesterday morning has developed a closed circulation, low-level spiral bands, and an increasing amount of heavy thunderstorms. While this morning's ASCAT pass does not show a clear closed circulation, satellite estimates of 96L's strength support calling this a 30 mph tropical depression. It is likely that this storm will be designated Tropical Depression Seven later today. 96L is already bringing heavy rain and strong, gusty winds to the southern Cape Verde Islands. Winds were sustained at 26 mph at Mindelo in the northwest Cape Verde Islands this morning, and 24 mph at Praia, the station closest to the center of 96L. Both stations were reporting widespread dust, due to strong winds blowing Saharan dust from the coast of Africa. However, water vapor satellite images show that only a modest amount of dry air is accompanying this dust, and dry air is currently not a major detriment to 96L. Wind shear is about 10 - 20 knots, and sea surface temperatures are warm, 28°C.

Forecast for 96L/Tropical Depression Seven
Wind shear is predicted to remain low, 5 - 10 knots, for the next four days. SSTs will cool a bit to 27°C by Thursday, but this is still above the 26.5°C threshold for hurricane development. Dry air will probably be the main inhibiting factor for 96L. Most of the intensity forecast models bring 96L to hurricane strength by four days from now, and this is a reasonable forecast. 96L should become Tropical Storm Earl later today or on Wednesday, and will probably bring sustained winds of 40 mph to the southernmost Cape Verdes Islands tonight and Wednesday.

The long range fate of 96L remains unclear. The storm is being steering by the same ridge of high pressure steering Danielle, and will initially follow a track similar to Danielle. 96L may encounter the cold waters stirred up by Danielle at times this week, inhibiting development. As 96L approaches the central Atlantic five days from now, the storm will encounter the same mid-Atlantic trough that will be steering Danielle, and 96L should turn more to the northwest. It is unclear at this point whether this trough will be strong enough to fully recurve 96L out to sea, east of Bermuda. This will, in part, depend upon how strong Danielle gets. A stronger Danielle is likely to create more of a break in the ridge of high pressure steering 96L, encouraging the storm to turn north and recurve out to sea. A weaker Danielle will make 96L more likely to miss recurvature, and follow a track to the west or west-northwest towards the U.S. East Coast early next week. History suggests that a storm in 96L's current location has only a 20% chance of making landfall on the U.S. East Coast.

When will the Caribbean and Gulf of Mexico get active?
The large scale atmospheric circulation over the Caribbean and Gulf of Mexico currently features relatively dry, stable, sinking air. This is due, in part, to the Madden-Julian oscillation (MJO). The Madden-Julian oscillation is a pattern of enhanced rainfall that travels along the Equator from west to east. The pattern has a wet phase with large-scale rising air and enhanced thunderstorm activity, followed by a dry phase with large-scale sinking air and suppressed thunderstorm activity. Each cycle lasts approximately 30 - 60 days. When the Madden-Julian oscillation is in its wet phase over a hurricane-prone region, the chances for tropical storm activity are greatly increased. The latest MJO forecast from the GFS model calls for the wet phase of the MJO to move into the Caribbean during the first week of September. However, keep in mind that forecasts of MJO activity 1 - 2 weeks in advance are not very skillful. The GFS model forecast of MJO activity made two weeks ago did fairly well for the first week, but poorly for the second week of the forecast.

Tropical Storm Frank spares Mexico
Over in the Eastern Pacific, Tropical Storm Frank has moved away the coast far enough from the Mexican coast to no longer pose a heavy rainfall threat, and all tropical storm warnings have been dropped.

"Hurricane Haven" airing again this afternoon
Tune into another airing of my live Internet radio show, "Hurricane Haven", at 4pm EDT today. Listeners will be able to call in and ask questions. The call in number is 415-983-2634, or you can post a question in the comments area on my blog during the show. You can also email the questions to me today before the show: jmasters@wunderground.com. Be sure to include "Hurricane Haven question" in the subject line. I'll focus on Danielle, Earl, and Frank, and discuss the possibilities of a hyperactive Atlantic hurricane period coming during the first week of September.

Today's show will be 30 - 45 minutes, and you can tune in at http://www.wunderground.com/wxradio/wubroadcast.h tml. The show will be recorded and stored as a podcast.

Jeff Masters

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If TS Earl forms today--as appears somewhat likely--that means we're not so far behind 2008, which was "only" on the 'F' storm on this date. (Of course, Gustav formed on the 25th, but still, we're not way behind...)
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Just as i said, wind shear & dry air.. then i get people quoting me and poofing me, It's like you guys hate hearing the truth when it comes to storms weakening, just suck it up, not every storm can be a major hurricane.
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Quoting Rockportshrimper:
If your a legit Met or even a hobby Met, why would a fish storm be less interesting than a storm that threatens people, places and things? Why does a TS have to be a "killer" before it becomes interesting to many in this group? Wind shear, dry air, steering currents -all the same science applies.

If it bleeds it leads? Sad


Agreed
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wow on the RBG floater Danielle looks like a V with an eye in the middle
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If your a legit Met or even a hobby Met, why would a fish storm be less interesting than a storm that threatens people, places and things? Why does a TS have to be a "killer" before it becomes interesting to many in this group? Wind shear, dry air, steering currents -all the same science applies.

If it bleeds it leads? Sad
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StormW, is your synopsis up yet?
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How about that LP system in Canada. Thats the big player.

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Quoting Cotillion:
THE PERIOD OF RAPID INTENSIFICATION HAS ENDED WITH A THUD. THE
LOW-LEVEL CENTER OF DANIELLE HAS BECOME EXPOSED BETWEEN A RAGGED
CENTRAL DENSE OVERCAST TO ITS EAST...AND A BROKEN CONVECTIVE BAND
TO ITS WEST. ALL ALONG...MICROWAVE IMAGERY SINCE ABOUT 0300 UTC
SHOWED A DRY SLOT WRAPPING AROUND THE WESTERN AND SOUTHERN SIDE OF
THE CIRCULATION...AND AS A RESULT THE EYEWALL BECAME ERODED. DATA
T-NUMBERS HAVE FALLEN QUICKLY AND ARE NOW AS LOW AS T3.9 FROM THE
HURRICANE INTENSITY ESTIMATE...AN EXPERIMENTAL FORM OF THE UW-CIMSS
ADT. THE INITIAL INTENSITY IS LOWERED TO 70 KT AT THIS TIME...
WHICH COULD STILL BE GENEROUS.

Score one for the downcasters on here this am..lol
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Quoting nola70119:


They forecast a Cape Verde storm would develop around August 23rd.....I could have forecast something like that a year ago.


LOL ....and if you had forecast it would mis the US coast U would have had an 80% chance of being right........
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Quoting WarEagle8:

Yes, we have had 4+ inches in Dunedin, FL since Saturday. Sat = rain off and on all day, Sun = several strong bands, Mon = heavy after 5P and non-stop since then... radar looks interesting. Anything developing to our west in the GOM?
You guys are on the "wet"
side of frontal boundary..we have dry air advecting in behind this boundary in north gulf coast..Noth winds and much drier air..nice!
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'The Most Interesting Man in the World' must've got on a boat and breathed on TC Danielle.

What other explanation could there be...
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Anybody: Why no Weather 456 input lately? Personally, I miss reading his blog.
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HURRICANE DANIELLE DISCUSSION NUMBER 12
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL062010
1100 AM AST TUE AUG 24 2010

THE PERIOD OF RAPID INTENSIFICATION HAS ENDED WITH A THUD. THE
LOW-LEVEL CENTER OF DANIELLE HAS BECOME EXPOSED BETWEEN A RAGGED
CENTRAL DENSE OVERCAST TO ITS EAST...AND A BROKEN CONVECTIVE BAND
TO ITS WEST. ALL ALONG...MICROWAVE IMAGERY SINCE ABOUT 0300 UTC
SHOWED A DRY SLOT WRAPPING AROUND THE WESTERN AND SOUTHERN SIDE OF
THE CIRCULATION...AND AS A RESULT THE EYEWALL BECAME ERODED. DATA
T-NUMBERS HAVE FALLEN QUICKLY AND ARE NOW AS LOW AS T3.9 FROM THE
HURRICANE INTENSITY ESTIMATE...AN EXPERIMENTAL FORM OF THE UW-CIMSS
ADT. THE INITIAL INTENSITY IS LOWERED TO 70 KT AT THIS TIME...
WHICH COULD STILL BE GENEROUS. SHIPS GUIDANCE SHOWS WESTERLY TO
SOUTHWESTERLY SHEAR INCREASING TO BETWEEN 15 AND 20 KT OVER THE
NEXT 24 HOURS OR SO...AND IT IS UNCLEAR HOW WELL DANIELLE WILL BE
ABLE TO MIX OUT THE DRY AIR. ONLY SLOW STRENGTHENING IS INDICATED
IN THE OFFICIAL FORECAST...AND THE INTENSITY AT DAYS 4 AND 5 IS
HELD JUST BELOW MAJOR HURRICANE STRENGTH TO MAINTAIN SOME SORT OF
CONTINUITY...BUT THIS IS NOW ABOVE MANY OF THE INTENSITY MODELS.

MICROWAVE FIXES INDICATE THAT DANIELLE HAS BEEN MOVING QUICKLY WITH
AND A AN INITIAL MOTION ESTIMATE OF 290/17. THIS MOTION IS A
LITTLE TO THE LEFT OF THE FORECAST TRACK. LITTLE CHANGE IS
REQUIRED IN THE FORECAST...AND DANIELLE IS STILL EXPECTED TO TURN
TOWARD THE NORTHWEST THROUGH A WEAKNESS IN THE SUBTROPICAL RIDGE.
THE MODEL GUIDANCE REMAINS IN VERY GOOD AGREEMENT ON THIS SCENARIO.
THE OFFICIAL FORECAST TRACK LIES A LITTLE WEST OF THE PREVIOUS
FORECAST DURING THE NEXT 48 HOURS TO ACCOUNT FOR THE INITIAL MOTION
BUT THEN REMAINS CONSISTENT WITH THE EARLIER FORECASTS FOR DAYS 3
THROUGH 5. THIS SOLUTION IS VERY CLOSE TO THE MULTI-MODEL
CONSENSUS TVCN AND STILL A LITTLE LEFT OF THE GFS...GFDL...AND
HWRF...WHICH SEAMS REASONABLE GIVEN THE CONTINUED LEFT-OF-TRACK
MOTION.
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THE PERIOD OF RAPID INTENSIFICATION HAS ENDED WITH A THUD. THE
LOW-LEVEL CENTER OF DANIELLE HAS BECOME EXPOSED BETWEEN A RAGGED
CENTRAL DENSE OVERCAST TO ITS EAST...AND A BROKEN CONVECTIVE BAND
TO ITS WEST. ALL ALONG...MICROWAVE IMAGERY SINCE ABOUT 0300 UTC
SHOWED A DRY SLOT WRAPPING AROUND THE WESTERN AND SOUTHERN SIDE OF
THE CIRCULATION...AND AS A RESULT THE EYEWALL BECAME ERODED. DATA
T-NUMBERS HAVE FALLEN QUICKLY AND ARE NOW AS LOW AS T3.9 FROM THE
HURRICANE INTENSITY ESTIMATE...AN EXPERIMENTAL FORM OF THE UW-CIMSS
ADT. THE INITIAL INTENSITY IS LOWERED TO 70 KT AT THIS TIME...
WHICH COULD STILL BE GENEROUS.
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I say that danielle weakens move w-wnw then nw but not recurving yet

but I have a strong feeling that pre-TD7 will not follow the same fate and TD7 will remain weak untill it reaches 40-45W and will not have much of a northely componets till 45-55W but then back west all in all I don't expect this to make it north of 20N and east of 40-50W
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Quoting barotropic:
Per Dr. Masters post

"History suggests that a storm in Danielle's current location has only a 20% chance of making landfall on the U.S. East Coast. If Danielle passes east of Bermuda, as forecast, these percentages drop to less than 5%.

The formation of Danielle is remarkable in this it was successfully forecast by the GFS model nearly two weeks in advance. The ECMWF and NOGAPS models also did a good job of predicting Danielle's formation a week in advance. The models are getting better and better each year at forecasting genesis of tropical cyclones, though a successful 1-week forecast of genesis is still a rarity"

"A powerful trough of low pressure over the mid-Atlantic Ocean will begin to pull Danielle more to the northwest by Wednesday, keeping Danielle well to the east of Bermuda. Most of the models predict that this trough will be strong enough to fully recurve Danielle out to sea. It is possible that Danielle could eventually threaten Newfoundland, Canada, but it currently does not appear that any other land areas will be at risk from this storm".


Uh Oh Dr. Masters is downcasting!! LOL. His comments echo what I have said and Ike has been saying and some other on here. The GFS, and even more so the GFDL and HWRF have been very close in an accurate track for danielle since the 8/22 06z runs. The earlier runs were depicting a storm that had had not really even developed yet and had it moving in a NW motion quite early over and over again. I believe for a mid oceanic storm the models have been fantastic and have up to this point done their job quite well, looks like Dr. Masters agrees.


They forecast a Cape Verde storm would develop around August 23rd.....I could have forecast something like that a year ago.
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SUBJECT: "FRANK" Strengthens As It Moves Away From Mexico

At 15:00 PM UTC, Tropical Storm Frank (994 hPa) located at 15.3N 100.9W or 200 NM southwest of Acapulco, Mexico has sustained winds of 55 knots with gusts of 65 knots. The cyclone is reported as moving west northwest at 6 knots.

Storm Force Winds
================
95 NM from the center

Forecast and Intensity
=========================
24 HRS: 16.5N 104.4W - 65 knots (SVR Tropical Cyclone SSHS-1)
48 HRS: 17.9N 107.6W - 70 knots (SVR Tropical Cyclone SSHS-1)
72 HRS: 19.1N 110.5W - 70 knots (SVR Tropical Cyclone SSHS-1)
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Quoting PensacolaDoug:



Yes he did but in yesterdays post he admitted to not paying much attention to it as the forecast has it not affecting many people.
I submit that he still isn't giving it much thought and is just playing the percentages.


It sounds like he is just reiterating what the NHC is saying....which may in the end be correct, or not.

I am interested to see what Storm says today. I keep thinking it weakened just in time to go further West.

We will see.
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Storm - help me wrap my head around what your are saying vs. the others on here regarding Daniele.....and I by no means am knocking the NHC or other qualified Mets.....you feel the curve will come later in the game vs. what the NHC forescast is showing? Is the US still out of the picture? Thanks Chief.
Member Since: September 5, 2007 Posts: 0 Comments: 3481
Quoting clwstmchasr:
Dry stable air over the GOM???? It has been raining for over 24 hours on the West Coast of Florida!


Yes, we have had 4+ inches in Dunedin, FL since Saturday. Sat = rain off and on all day, Sun = several strong bands, Mon = heavy after 5P and non-stop since then... radar looks interesting. Anything developing to our west in the GOM?
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Per Dr. Masters post

"History suggests that a storm in Danielle's current location has only a 20% chance of making landfall on the U.S. East Coast. If Danielle passes east of Bermuda, as forecast, these percentages drop to less than 5%.

The formation of Danielle is remarkable in this it was successfully forecast by the GFS model nearly two weeks in advance. The ECMWF and NOGAPS models also did a good job of predicting Danielle's formation a week in advance. The models are getting better and better each year at forecasting genesis of tropical cyclones, though a successful 1-week forecast of genesis is still a rarity"

"A powerful trough of low pressure over the mid-Atlantic Ocean will begin to pull Danielle more to the northwest by Wednesday, keeping Danielle well to the east of Bermuda. Most of the models predict that this trough will be strong enough to fully recurve Danielle out to sea. It is possible that Danielle could eventually threaten Newfoundland, Canada, but it currently does not appear that any other land areas will be at risk from this storm".


Uh Oh Dr. Masters is downcasting!! LOL. His comments echo what I have said and Ike has been saying and some other on here. The GFS, and even more so the GFDL and HWRF have been very close in an accurate track for danielle since the 8/22 06z runs. The earlier runs were depicting a storm that had had not really even developed yet and had it moving in a NW motion quite early over and over again. I believe for a mid oceanic storm the models have been fantastic and have up to this point done their job quite well, looks like Dr. Masters agrees.
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Quoting jrweatherman:


So you are saying to Dr M. is wrong and that we all should ignore his post?
seems that we have pretty good consensus among the experts that the system will curve out to sea somewhere between 50-55w. he justs likes to go against the grain but does not provide us with much science as to why. the weakness is pretty easy to see on wv and should do the job even if it moves a little more west that was earlier predicted.
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Member Since: July 31, 2006 Posts: 19 Comments: 1563
Quoting katrinakat5:
btwntx is been eating crow since this season began lol..



Tastes like chicken!
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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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