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Danielle a hurricane; TD 7 forming off coast of Africa

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

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

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

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1149. xcool

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1148. Engine2
Is the center relocating to the southwest?
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1144. SeaMule
there will be a continued westerly shift to the models...until they finally realize Danielle is heading for Miami. if they wait too long, it'll be too late to get beer.
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Do you know what's happening in the GOM? Why it fired up?
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If you read carefully below, you will see the NHC now stating models this and that; however you want to read into it, I read between the lines, we at the NHC were not wrong, the models were wrong if this thing keeps going west. I really do think the NHC is preparing for this eventuality, lets play the blame game.

What do I think will happen, the storm gets much closer to the U.S., at least a scare, you will see the NHC baking off the turn north ever spo slightly over the next day or so, until no turn is forecasted.

I am not stating a conspiracy theory, just saying the NHC does not want to look like they got it wrong in the end. You will see this happening, so be prepared. Please do not ask me to back this all up, because I am just going by gut as of now.

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1140. xcool
CoopNTexas.hey friend
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1138. xcool

I wouldn't be suprised to see more west shift ...
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while there is oohs and aahs about two fish storms, the CMC, EURO have hinted and now NAM jumps on board about GOM action in a few days.

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1135. Zeec94
Well I have to admit, I was WRONG about Danielle. So for that great job Levi, StormW, and all the others.

My predictions on 96L however have changed a bit. (Yes ITS STILL 96L NOT Earl) ;)

I think it has a lot better chances of heading towards the US coast. I still feel it will be a fish storm, but it will get farther than Danielle will to the US Coast.
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Quoting mojofearless:

The blog keeps eating this post.
Anyway - no, New Orleans was not in the cone on the Thursday before Katrina.
felt my blood pressure rising as I went through that frame by frame...wow what a change in tracks....don't ever wanna see that again...
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1133. angiest
Quoting KanKunKid:

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

If jstrack has a way to show the old forecasts I don't know. it certainly has that information, since you can see the forecast for Danielle.
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Quoting dan77539:

If it wasn't clear, I meant my company subscribes to Impact, not that I work there. LOL

Oh, I wasn't accusing you of anything...LOL
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Quoting KanKunKid:
Does anyone have an Excel spreadsheet that plots lat lon points and puts them on a chart?
I wrote a utility a few years ago that exports an Excel spreadsheet full of lat/lon pairs to Google Earth or Google Maps. Something like that? You can find them on Google...
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Congrats to StormW, Levi, and others who
respectfully disagreed with "model concensus"
and as Levi kept saying..Bermuda should keep
watching D's progress..My Question now is
if Danielle weakens further and slows...can we expect another west shift in
Models tonight?
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1126. IKE
Quoting barotropic:

I didn't disagree with you???

I don't mean you I mean him. I know...you agreed.
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1125. Engine2
I wonder if the center is redeveloping in the SW area of the convection firing? That would be interesting

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Quoting StormW:

Make sure you depress the clutch, first.

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1122. angiest
Click to see the full images. The first I took last night:

danielle and ike

The second I captured a few minutes ago:

danielle and ike v2
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Here is the water vapor a little distorted to exaggerate the contrast, but the same picture none the less:

Image and video hosting by TinyPic

here is the original non distorted image:

Tons of moisture over the Caribbean, and a fair amount of dry air ahead of Danielle.
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Quoting IKE:

Gosh I'm glad he's on my ignore list. He'll disagree with everything I say....whether I'm right or wrong and I'm wrong quite a bit as an amateur.

I didn't disagree with you???
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She's baaackkk !!!
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TropicalStormDanielle's heading has turned northward to 8.4degrees north of WestNorthWest
from the previous heading of 5.1degrees north of WestNorthWest

23Aug - 09pmGMT - 15.4n41.5w - - 75mph . . . . . 987mb - NHC.Adv.9
24Aug - 12amGMT - 15.5n42.3w - - 75knots . . . . 982mb - NHC-ATCF
24Aug - 03amGMT - 15.6n43.2w - - 85mph . . . . . 982mb - NHC.Adv.10
HurricaneDanielle becomes Cat.2
24Aug - 06amGMT - 15.7n44.0w - - 85knots . . . . 973mb - NHC-ATCF
24Aug - 09amGMT - 15.9n44.6w - - 100mph . . . . 973mb - NHC.Adv.11
24Aug - 12pmGMT - 16.1n45.8w - - 75knots . . . . 983mb - NHC-ATCF
24Aug - 03pmGMT - 16.6n46.5w - - 80mph . . . . . 985mb - NHC.Adv.12
24Aug - 06pmGMT - 17.1n47.5w - - 65knots . . . . 990mb - NHC-ATCF
H.Danielle becomes TS.Danielle
24Aug - 09pmGMT - 17.5n48.2w - - 70mph . . . . . 993mb - NHC.Adv.13

~69.6knots=80mph _ _ _ 65knots=~74.8mph _ _ _ ~60.9knots=70mph
NHC rounds windspeeds to the nearest 5mph or to the nearest 5knots

Copy&paste 15.9n44.6w-16.1n45.8w, 16.1n45.8w-16.6n46.5w, 16.6n46.5w-17.1n47.5w, 17.1n47.5w-17.5n48.2w, bda, nas into the GreatCircleMapper for a look at the last 12hours.
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1114. IKE
I remember 3-4 days ago the models...CMC...NOGAPS...ECMWF and GFS, had Danielle crossing 20N, near 50W.

NHC new track has it crossing 20N at about 51.8W.
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Danielle looks better than when she was a hurricane! NRL has it on 65 kts (Cat 1 hurricane).
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poor Bermuda, what did you do too get this

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take that fishcasters
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1108. Halyn
Quoting TerraNova:

Yeah same here!
Me, too, Storm.. :) Better late than never .. :)
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1107. IKE
Quoting barotropic:

Its not that important anyway...no biggie at all

Gosh I'm glad he's on my ignore list. He'll disagree with everything I say....whether I'm right or wrong and I'm wrong quite a bit as an amateur.
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Quoting MiamiHurricanes09:
Lol. What were you're coordinates? I had it at 17.4N 47.9W...turns out I was to the south and west of the circulation.

Definitely didn't see it near 17.0N as some were stating.
As I said yesterday..this storm will be a good study after its all over... now let's see where it goes...
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weaker = west?? right?
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Quoting TerraNova:

Yeah same here!
I've been lurking here sincew 2005, Storm is a gentleman in all the sence of the word,he is humble,and shares his knowledge without bashing people or having ego attacks toward people that are just interested and one to enhance their knowledge on the subject. The other day he did told Dr. Masters that he read his update because their were coinsidence in their forecast. Great, I'm sure that the good Doc was proud, because they are both professionals( I consider Storm a professional, even if he does't have a Met. title) and are above little petty stuff
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looks like are storm is heading for Bermuda,
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NHC still on the right side of the model consensus, staying conservative at the least.
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Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather

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