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 StormW:


You betcha, Shen...we got jeans, T-shirt, and your choice of bandanna.


Can I be too lol
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1197. pottery
Quoting SFlKatCane5:


Are you serious? Danielle to Cat 4 or 5? That's ridiculous!

Can you READ???
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Quoting StormW:


You betcha, Shen...we got jeans, T-shirt, and your choice of bandanna.


I'll donate $20 to charity of your choice for a picture of you in said bling.
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1195. swlavp
Quoting ROBTX09:
i bet ike took notice fast if not ok but i agree with u sometimes ike but not all the time
I hope that you don't have as many different names as Jason!
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Quoting StormW:


You betcha, Shen...we got jeans, T-shirt, and your choice of bandanna.
More importantly, can we wear Flip Flops?
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1193. Max1023
Danielle looks better now than any other time since 12z. It appears to be trying to reorganize with a strong convective burst occurring slightly to the east of the center, with the center itself on the edge of the convective mass. I speculate that the westerly shear was caused by Danielle reaching an environment with low upper level winds. Prior to last night Danielle's forward motion was contrary to the shear direction, however today her fast WNW motion induced westerly shear on the cyclone, which is evident now. Based on the cloud pattern I believe that when Danielle slows down in response to the weakness she will fully reorganize as the shear relative to the storm motion will decrease. As well, slower forward motion reduces the affects of dry air entrainment as the outer bands have more time to add moisture to the vicinity of the storm before the core moves over the area.

I believe that Danielle will re-attain hurricane strength by 06Z tonight and will intensify by about 5-10 knots every 6 hours thereafter until reaching about 90knot intensity.

Just my opinion btw, I am not a Met.
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Quoting DarIvy959810:
According to Dr Masters:
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. Danielle weakens!
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Quoting IKE:
ECMWF only gets her to about 58W....

Shifts towards the left can be anticipated, I really doubt that we will see a track like that.
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Quoting MoltenIce:
It's a tropical depression in my opinion.

Where his center ? It is disorganized
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1188. pottery
Quoting Floodman:


Damn, brother, the Limo gettin' full!

I really dont mind settin' in the trunk, if it's OK with youall...
(please??)
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Quoting Floodman:


Damn, brother, the Limo gettin' full!
Don't be worry bout me. I be in the chase Hummer.
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So... now she is a tropical-storm... therefore more west... therefore closer to Bermuda and Maritimes.
What a wierd season.

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1185. IKE
ECMWF only gets her to about 58W....

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I mean, FL is all of a sudden looking like CV.
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According to Dr Masters:
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.
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1181. angiest
Quoting angiest:


Forecasts for Ike at initial advisory and first advisory as hurricane overlain on the track.

Photobucket


And similarly for Danielle. First advisory and first advisory as a hurricane:
Photobucket
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting ShenValleyFlyFish:
He StormW can I be in your posse too? What kind of Bling we got to wear?


Damn, brother, the Limo gettin' full!
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Storm, you seeing any kind of cyclogenesis in the GOM later this week?
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1175. smuldy
Quoting MiamiHurricanes09:
Quite the spread on the ECMWF ensembles, shows that Danielle could affect anywhere from 27N 80W (north of the Bahamas) to 40N 45W (SE of Newfoundland) with the bulk of the ensemble members taking it very near Bermuda, if not a Bermuda landfall.


12z ECMWFENS 144 hours:

the euro finally shifts; it will be interesting to see the forward speed she maintains over the next 24 hours in regards to where that second trof is forming, bermuda needs to pay a close eye, but given the westward trending and forward speed no one should shut both eyes, yet
Member Since: July 23, 2010 Posts: 0 Comments: 524
Hey StormW can I be in your posse too? What kind of Bling we got to wear?
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1173. pottery
Greetings all.
I missed the earlier Bacchanal?
Thank Goodness for that...

Danielle is suffering from the Ingestion of Dry Air.??
Well, I thought she might.
Could not see how she was going to deal with that.
Hurricanes need water in the atmosphere.
Or so I was told, anyway.

On another note, 2" of rain here today has the place at 100% humidity right now.
Steam-bath time....
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1172. IKE
Quoting FLdewey:
It's nice when they warn you ahead of time.


LOL!
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Quoting Dakster:


Flooman,

After reading back, where did all the Danielle, Cat 5, Westcasters go?

Storm - Add me to the list too...


You know how it goes...too much pressure an "POP goes the weasel!"

LOL

Glad to see you in here more these days...
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1168. angiest
Quoting KanKunKid:


You wouldn't happened to have an overlay of the forecast track vs actual wood ya?


Forecasts for Ike at initial advisory and first advisory as hurricane overlain on the track.

Photobucket
Member Since: August 26, 2006 Posts: 16 Comments: 4766
No, a front is HERE, in centex, finally dropping the temps from 105 an hour ago to 80 right now... the stuff in the GOM looks like outflow from ?something?
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1166. xcool
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1165. IKE
Quoting FLdewey:

Good to know.


Sure was.
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1163. calder
Jeff was excellent on the radio tonight. Still think Danielle will pass to the east of bermuda but this is certainly becoming a much more interesting tracking situation!

Quoting ROBTX09:
aka btwntx08 and no i didnt get ban on my other i just wanted to try out this account i wanted use it in a long time


PS: so bored of the constant drivel....

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Quite the spread on the ECMWF ensembles, shows that Danielle could affect anywhere from 27N 80W (north of the Bahamas) to 40N 45W (SE of Newfoundland) with the bulk of the ensemble members taking it very near Bermuda, if not a Bermuda landfall.


12z ECMWFENS 144 hours:

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Hmmmmm, is interesting.

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1159. Dakster
Quoting Floodman:


Wow, Storm! You appear to have a few friends here...add me to the list, by the way...


Floodman,

After reading back, where did all the Danielle, Cat 5, Westcasters go?

Storm - Add me to the list too...
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I'm just a lurker here, i never actually thought that i would post a comment. I really like to look for stormw's posts on here. I also like to see patrap and levi's posts. i'm enjoying the site for the most part. I am not a forecaster, wishcaster, westcaster etc.....lol. i am just very interested in tropical weather, plus i work on a drilling rig in the GOM. I really don't like to see storms headed this way because it is way to much work to rig down and evacuate for a storm. Not to mention the danger to people. i may have some questions but that will be it. does 96L look like it may be headed for the conus once it does form?
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1157. xcool
ROBTX09 ha
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It's a tropical depression in my opinion.
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Cooleo...action in the GOM.
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1151. xcool
ROBTX09 ?
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1149. xcool


xcool
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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.