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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Quoting PensacolaDoug:
Not sure what's up in the world but here in central NJ just had three straight occurrences of pairs of F16s go screaming overhead - heading southward in a big big hurry - just in the past five minutes.


Six F/A18's (aka The Blue Angels) just finished their Tuesday morning practice. They roared low overhead at least 10 times in the last hour. That never gets old!

Amen!
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Quoting btwntx08:

looks like it wont lol


So you are saying to Dr M. is wrong and that we all should ignore his post?
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Quoting jrweatherman:
Okay, Dr. Masters says the strong trough will pick up Danielle and carry her out to sea.

Thanks for straightening us out Dr.



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.
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Hurricane season hasn't quite revved yet, this is just a throttle blip. I'd say next 7-10 days should be interesting though...
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I guess like many things, model performance is in the eye of the beholder. One measure that could be used is the NHC cone of error, a set of circles which "is set so that two-thirds of historical official forecast errors over the most-recent 5-year sample fall within the circle". For 2010 the radii for the 120 hour forecast is set at 285 nautical miles. To look back at model forecasts one can use the NCEP/EMC Cyclogenesis Tracking Page .
The most recent position fix for Hurricane Danielle is 16.1N, 45.8W at 12Z. Using the NCEP page and selecting the "Text" box to look at model positions:
GFS 5 day (120 hour) forecast from 2010081912 17.0N, 46.0W. Entering the current and forecast positions in this Distance Calculator shows 102.3 kilometers, or 55.24 nautical miles. Doing the same for
GFS 6 day (144 hour) forecast from 2010081812 15.6N, 48.2W, 141.85 nautical miles
GFS 7 day (168 hour) forecast from 2010081712 17.0N, 57.2W, 658.21 nautical miles
So only after the 6 day forecast did the GFS exceed the NHC 5 day historical error.
Image plots for these model cycles
2010081912
2010081812
2010081712
Member Since: September 23, 2005 Posts: 15 Comments: 11343
Danielle will have a big impact on where 96L will go. Cooler waters churned up by Danielle will keep 96L week IMO and move west. Not a good scenario for the east coast. Just my honest opinion
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Quoting P451:
Not sure what's up in the world but here in central NJ just had three straight occurrences of pairs of F16s go screaming overhead - heading southward in a big big hurry - just in the past five minutes.

_________

As to Danielle, she looks pretty ragged at the moment.




I'm in Essex County and I didn't hear anything, must have come from McGuire Air Force Base.
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Quoting katrinakat5:
lol storm w vs bob and the NHC


LOL. Oh I think the NHC has done well with this one. Its easy when all the models agree!..LOL Intensity forecasts are another story, still very hard to judge.
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thanks for update doc
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The Weaker Hurricane Danielle is the LESS likely to recurve. It seems to be falling apart like every other storm this year. I would not be surprised if it gets downgraded to a strong toprical storm in 12-24 hours and takes a more southerly route
Member Since: August 21, 2008 Posts: 0 Comments: 143
Quoting StormW:


Sorry this time Bob..gotta disagree.


No problem, even Dr. Jeff says the models have done well. But the possibility is still there that this comes closer to Bermuda, I wont disagree with that. Glad we wont have to worry about this one here in the U.S..
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Quoting P451:


Just had two more pairs scream by. Not sure what they're up to. I'll get a pair going by about once a month running exercises but never seen what we just had.

Seems amiss.



MrWONDNewsman Gearing up for the Atlantic City Airshow Thunder Over The Boardwalk. Begins at 10am on Newstalk 1400 WOND!!
about 1 hour ago via Twitter
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Okay, Dr. Masters says the strong trough will pick up Danielle and carry her out to sea.

Thanks for straightening us out Dr.
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Quoting StormW:


Sorry this time Bob..gotta disagree.


StormW versus Bob
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Quoting PensacolaDoug:
Not sure what's up in the world but here in central NJ just had three straight occurrences of pairs of F16s go screaming overhead - heading southward in a big big hurry - just in the past five minutes.


Six F/A18's (aka The Blue Angels) just finished their Tuesday morning practice. They roared low overhead at least 10 times in the last hour. That never gets old!


Was in Va Beach 3 weeks ago when the USS Eisenhower returned from deployment and had 5 squadrons of F-18's come in over the beach on their way to Oceana Naval Airstation over a 2-3 hour period-AWESOME
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Quoting weatherguy03:
Thanks Doc.

From the previous blog I wrote..LOL:

As far as model verification so far, and the NHC track, since Danielle developed, everything looks pretty good. Some slight deviations, but nothing drastic which is nice when it comes to forecasting. The last 24 hours we have seen the models very slightly move West, as far as whether this affect Bermuda or not. I believe there will be two main forecasting caveats with this system, does it come close enough to Bermuda to affect them with TS or Hurricane force winds, and will this Westerly shear continue today(seems like its coming in alittle sooner then forecasted), thus weaken Danielle and she wont become a Major. Other then that its a pretty simple forecast.

Got lost in the shift!


A sensible forecast - sensible because it comes from an experienced met. Agree with you 100%. Nice videos too, I'm hoping to get a link set up from our station onto here.
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Let us not forget the significance of this date. Here in Miami we are observing the 18th anniversary of Hurricane Andrew, which changed the lives of so many people here.

A lot of us still divide our history in terms of pre or post Andrew.
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NHC isn't going to start advisories on 96L this morning. They said because the ASCAT pass didn't show a clear closed center, basically what Dr. Master's just said. They will probably start advisories in the afternoon, and obviously Danielle has weakened and more so than what they will set the intensity to.
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Looks like Hurricane season is here and revved up
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Excellent and well put together as usual Doc. Thanks again
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Quoting PensacolaDoug:
Not sure what's up in the world but here in central NJ just had three straight occurrences of pairs of F16s go screaming overhead - heading southward in a big big hurry - just in the past five minutes.


Six F/A18's (aka The Blue Angels) just finished their Tuesday morning practice. They roared low overhead at least 10 times in the last hour. That never gets old!

Cool.. Thank you for posting the info.
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If we are going to have a true upward pulse of the MJO in the first week of September, things could get really interesting.
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Not sure what's up in the world but here in central NJ just had three straight occurrences of pairs of F16s go screaming overhead - heading southward in a big big hurry - just in the past five minutes.


Six F/A18's (aka The Blue Angels) just finished their Tuesday morning practice. They roared low overhead at least 10 times in the last hour. That never gets old!

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Quoting FLdewey:

Agreed I can't believe it's been that long. I very vividly remember the sound of the roof trusses as they failed one by one. I still get chills when I hear loud wood cracking.


When people ask me what it sounds like(trusses Failing) I ask them if they have ever pulled a nail out of a thick piece of wood and it has that ear piercing screech. They usually answer yes. Then I say multiply that times ten thousand and factor in the wind sreamin through the trees. that,s what it sounds like.
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Thanks Dr. M. Will be tuning in later today.
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Thanks Doc.

From the previous blog I wrote..LOL:

As far as model verification so far, and the NHC track, since Danielle developed, everything looks pretty good. Some slight deviations, but nothing drastic which is nice when it comes to forecasting. The last 24 hours we have seen the models very slightly move West, as far as whether this affect Bermuda or not. I believe there will be two main forecasting caveats with this system, does it come close enough to Bermuda to affect them with TS or Hurricane force winds, and will this Westerly shear continue today(seems like its coming in alittle sooner then forecasted), thus weaken Danielle and she wont become a Major. Other then that its a pretty simple forecast.

Got lost in the shift!
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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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