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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Hi all, just thought i'd submit something for once instead of asking questions: Maybe someone can tell me how to post images because it doesnt seem to be working, thanks :)

00z
http://raleighwx.easternuswx.com/models/atcf/00zatcflateinvest1.gif

06z
http://raleighwx.easternuswx.com/models/atcf/06zatcflateinvest1.gif

12z
http://raleighwx.easternuswx.com/models/atcf/12zatcfearlyinvest1best.gif
Member Since: Posts: Comments:
Danielle is still moving at 20 mph. It needs to slow down before it starts to make that turn, should do so later on today, but not as quick as the models and NHC have it doing. I'm leaning on the southern side of the model consensus.
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144. 7544
d is moving west again ?
Member Since: May 6, 2007 Posts: 0 Comments: 6690
143. IKE
Does this song apply>>>>????

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It looks like the dry air to the west and east are contributing to the raggedness of Danielle. I would like someone to explain to me why so many models are expecting Danielle to start the hard right turn so soon. As I review the water vapor imagery from the Tropical Atlantic, it appears that Danielle is still under the control of the ridge to it's NW. If that's the case, what are the steering mechanisms that are going to swing it out of it's current track for at least 12 to 18 hours?

Link
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Could expect TD7 in the next update.
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Quoting all4hurricanes:
Why isn't 96L a depression it meets all the criteria



Maybe the next outlook, they mention it as a depression.
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Beware the SAPD!
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Quoting btwntx08:
118:poof not needed
omg you poofed me. what will i ever do without you?? lighten up FRANCES.
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PRE-TD7 I expect it to move SW between now and the next two day oh yeah is people think I am asking well I am NOT I am telling you guys
Member Since: June 13, 2009 Posts: 2 Comments: 11033
Why isn't 96L a depression it meets all the criteria
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so if someone mentions that it is raining in their area, is that relevant?

Come on man, lighten up
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Quoting btwntx08:
102:reported off topic image



petty....
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18 YEARS AGO TODAY..... Link
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Quoting KerryInNOLA:
A lot of "hobbyists" keep saying it will go further west than what the NHC says. Have you ever seen the inside of the Center? It is 23rd century. They are the pros with the degrees, brains and large salaries to boot. They are doing their jobs giving us cutting edge forecasts. We are allowed to discuss and debate, this is America, but remember they wear the pants.
if you read the NHC discussion they did say that the storm is currently west of the model guidance.
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Quoting btwntx08:

Admin Notice: When using Dr. Masters' blog, please refrain from posting material not relevant to the discussion of tropical weather, or the topic of the blog entry itself. Please do not engage in personal attacks or bickering. Material not conforming to these standards should be flagged with the button and ignored.


Accurately describes 50% of your posts...
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I agree that 96Ls future is unclear.





Really going out on a limb there....
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Quoting btwntx08:
102:reported off topic image


actually I thought it was a rather perfect response :0)
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1. SHOWERS AND THUNDERSTORMS CONTINUE TO BECOME BETTER ORGANIZED IN
ASSOCIATION WITH AN AREA OF LOW PRESSURE PASSING ABOUT 100 MILES
SOUTH OF THE CAPE VERDE ISLANDS...AND IT APPEARS THAT A TROPICAL
DEPRESSION COULD BE FORMING. IF THIS TREND CONTINUES... ADVISORIES
ON THIS SYSTEM COULD BE INITIATED AS EARLY AS LATER THIS MORNING.
THERE IS A HIGH CHANCE...90 PERCENT...OF THIS SYSTEM BECOMING A
TROPICAL CYCLONE DURING THE NEXT 48 HOURS AS IT MOVES
WEST-NORTHWESTWARD AT NEAR 15 MPH. LOCALLY HEAVY SHOWERS AND
STRONG GUSTY WINDS ARE POSSIBLE OVER PORTIONS OF THE CAPE VERDE
ISLANDS TODAY...AND INTERESTS IN THOSE ISLANDS SHOULD MONITOR THE
PROGRESS OF THIS SYSTEM.
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Did the NHC not declaire 96L a depression or are all the websites just slow
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114. wjdow
Quoting P451:


It's a public weather blog full of hobbyists, a handful of mets-to-be, and an even smaller handful of mets - who come here to discuss the weather.

This isn't a site to worship the NHC in all it's glory and defend them to the end. It's not the NHC or the NWS or any forecasting body to be used as a governing body in a life threatening situation.

It's a public discussion site.

Not so sure what the issue is that you're driving at.


I don't like the government any more than the next guy, but there's a kneejerk impulse by some on this blog to try to find cracks in NHC's logic and predicitions, and not much credit to NHC when they do well. The impulse sometimes extends to Dr. M. Can someone name a bad call by NHC this year or last?
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Quoting DarIvy959810:
Is it a TD yet or not in the coast of Africa
Not yet, but, the Navy issued a TCFA though and the NHC upped the probability to 90%.
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Quoting StormW:
000
WTNT31 KNHC 241442
TCPAT1
BULLETIN
HURRICANE DANIELLE ADVISORY NUMBER 12
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL062010
1100 AM AST TUE AUG 24 2010

...DANIELLE UNEXPECTEDLY WEAKENS...BUT FORECAST TO REGAIN
STRENGTH...


SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...16.6N 46.5W
ABOUT 985 MI...1585 KM E OF THE LESSER ANTILLES
MAXIMUM SUSTAINED WINDS...80 MPH...130 KM/HR
PRESENT MOVEMENT...WNW OR 290 DEGREES AT 20 MPH...32 KM/HR
MINIMUM CENTRAL PRESSURE...985 MB...29.09 INCHES


WATCHES AND WARNINGS
--------------------
THERE ARE NO COASTAL WATCHES OR WARNINGS IN EFFECT.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 1100 AM AST...1500 UTC...THE CENTER OF HURRICANE DANIELLE WAS
LOCATED NEAR LATITUDE 16.6 NORTH...LONGITUDE 46.5 WEST. DANIELLE IS
MOVING TOWARD THE WEST-NORTHWEST NEAR 20 MPH...32 KM/HR. A TURN
TOWARD THE NORTHWEST WITH A DECREASE IN FORWARD SPEED IS EXPECTED
DURING THE NEXT 48 HOURS.

MAXIMUM SUSTAINED WINDS HAVE DECREASED TO NEAR 80 MPH...130
KM/HR...WITH HIGHER GUSTS. DANIELLE IS NOW A CATEGORY ONE
HURRICANE ON THE SAFFIR-SIMPSON HURRICANE WIND SCALE. ALTHOUGH
DANIELLE HAS WEAKENED...RE-STRENGTHENING IS POSSIBLE DURING THE
NEXT 48 HOURS.

HURRICANE FORCE WINDS EXTEND OUTWARD UP TO 30 MILES...45 KM...FROM
THE CENTER...AND TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 140
MILES...220 KM.

ESTIMATED MINIMUM CENTRAL PRESSURE IS 985 MB...29.09 INCHES.


HAZARDS AFFECTING LAND
----------------------
NONE.


NEXT ADVISORY
-------------
NEXT COMPLETE ADVISORY...500 PM AST.

$$
FORECASTER BERG



StormW, Good Morning, I know your busy with a lot of questions but I am trying to understand this a little. Here's my ? if Danielle stays low in strength does that mean she could go more west and miss the trough, I mean the trough wouldn't influence her if she was little. Is that right? Then pre Earl could miss the trough to if he stays low in strength. You know I'm not a wishcaster or nothing like that just trying to wrap my head around it and understand.
Thanks for all you do,
sheri
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Is it a TD yet or not in the coast of Africa
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Pre TD-7.
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102. LOL!!!!
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12Z
Member Since: June 13, 2009 Posts: 2 Comments: 11033
Quoting teammc:
StormW, is your synopsis up yet?


yeah, I wanna know what Storm thinks is gonna happen to Dannielle!
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Quoting P451:


It's a public weather blog full of hobbyists, a handful of mets-to-be, and an even smaller handful of mets - who come here to discuss the weather....Not so sure what the issue is that you're driving at.


80-90% of the posts add nothing to the discussion.
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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...)
Member Since: November 8, 2009 Posts: 4 Comments: 13459

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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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