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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3049. RJT185
Thanks for the MJO data Storm, it'll be a HECK of a September for forecasters!
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3048. kramus
I'm off to work.

Class dismissed.
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The long-term track for Tropical Depression Seven is uncertain.
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Quoting StormW:


Be about a couple of hours...got another to get off to school this morning.

Glad I read through - I'll stay tuned as well. Would like to know what's going on in the Gulf.
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Stacked up like planes into LAX...

Click for larger image:
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TD 07L has declared.

1st advisor at 5AM EDT.




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Or should I say -
"erl is in the Gulf, we just can't see it anymore."
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3035. WxLogic
Here's the current setup and scenarios... I've marked with red circles in the current steering maps for Danielle the DLM highs that should guide TD7 and Danielle:



Scenario 1:

Danielle moves off to the NW to N in order to take advantage of the weakness to the N of her. This in turn allows the DLM High currently guiding TD7 to the W and then bridging with the High building soon over the E CONUS to replace the TROF that is currently in the process of weakening and as you can see allow TD7 to go further W than Danielle was able to.

Scenario 2
:

Danielle moves to the NW to N but is not able to take advantage of the weakness because either the DLM high intensifies enough to prevent too much northerly progress or Danielle decides to stall due to it not being strong enough (CAT2 or CAT3) to create a stronger weakness, but yet allowing enough weakness to allow TD7 to feel it. As you can see on this one, the E CONUS would be dominated by a DLM High and W Africa to C ATL dominated by a DLM high too. Yet around 50W you'll have a weakness that Danielle would have kept open to allow any "train" of tropical organized disturbances to lift up and move away from land.
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Earl is in the trunk.
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3033. hcubed
Quoting Michfan:


Your caps lock key is broken :P


That's not the only thing that's broken...
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For y'all playing along at home...

We have launched our live eTownHall: Surviving the Storm blog event at Pinellas County. You can enter your questions, and we'll do our best to answer them.

If you really want to bust a gut, you can check me out live tomorrow night at 7:00 p.m. as I moderate our panel discussion live on air.

The link is:

http://www.pinellascounty.org/eTownHall

Of course, if this violates the board rules, just lemme know....
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3029. breald
Quoting StormW:


(FISH)


Storm you think 7 will follow in Danielle's footsteps?
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3028. RJT185
Quoting hoenn:
TD 7 looking good, probley bill part 2! But I think it will not go the bill path, it will probley miss the weakness and hit florida and into the gulf of mexico.

Probably Bill part 2, but won't follow the Bill path? ... seriously?
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Quoting StormW:


(FISH)


is that your offishial position?
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Quoting StormW:


(FISH)



are you a fishcaster lol


this kinding
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3024. breald
Quoting klaatuborada:
I've been away for a while, and now I'm back, and if you remember it looked like we on the Cod were going to be back in drought but now we've finally gotten three days of rain! Glorious! Brown lawns green! Early defoliation stopped! Ground saturated! Now let's just hope it stops, lol!


Yes it needs to stop!! The dogs and I are getting depressed because we cannot spend anytime outside. One day of non-stop heavy rain would have been just fine. But this constant moderate rain for three days is a little much.
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Quoting hoenn:
TD 7 looking good, probley bill part 2! But I think it will not go the bill path, it will probley miss the weakness and hit florida and into the gulf of mexico.


Maybe...
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Good Morning/Evening

We finally broke our string of 90+ degree days. That set it from 41 to 46 days in a row. Thank goodness for the rain or there would be nothing but ash south of I-10. Back in the 90's again today, but it was great to have a cloudy break.

I liked the Haven show yesterday. Keep it up.
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Gaaaak! The Herbert fish shower curtain boxes!
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3018. surfmom
3011 Cot - LOL

"The other graph" - LOL
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3017. wjdow
Quoting DestinJeff:


OH.. STAND BY.





lol
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3016. fmbill
Quoting StormW:


I meant the other graphic (Hebert)


Oh no!!! Why did you have to say that? LOL!!!
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Quoting DestinJeff:


OH.. STAND BY.





Love the curtains :)
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3014. wjdow
Quoting DestinJeff:


OH.. STAND BY.



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Quoting StormW:


Or 0% if you worship the models.


Well, it is.

The GFS after all was a member of the Roman Pantheon.

Glaucus, Fortuna, Serapis. (Sea, luck and sky - about right for a model, surely?)

Everyone knows that!
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I've been away for a while, and now I'm back, and if you remember it looked like we on the Cod were going to be back in drought but now we've finally gotten three days of rain! Glorious! Brown lawns green! Early defoliation stopped! Ground saturated! Now let's just hope it stops, lol!
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I'm curious to see TD #7's path before I go to school this morning

Come on NHC!
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3005. surfmom
Quoting Tazmanian:



TD 7 has a pine hole eye
OMGOSH, claps hands, you are always so quick to see these things TAZ...thx!!
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3003. RJT185
Quoting StormW:


Or 0% if you worship the models.



**bows to the all mighty models** haha
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3001. surfmom
Quoting mydiapersarefull:
With 'soon to be named earl' following Danielle, there is the potential for surf all the way through the Labor Day weekend, meaning:

-red flag days throughout
-over 300 saves by lifeguards
-over 50 saves by surfers
-extra 500 idiots in the water


well said - I don't know about the surf all the way through to labor day - goodness you live in paradise - but I do agree w/the saves
it's why I beached myself yesterday -- water & wind was too rough - I never want our lifeguards to work more then necessary - got to RESPECT the power of the Water, Wind & WAVE
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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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