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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799. IKE
12Z ECMWF through 240 hours...
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Danielle looks like schnitzel.
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Quoting mydiapersarefull:
Hurricane Danielle Surf Forecast for Puerto Rico

the place to be...need ticket and vacation time!

ME too AMIGO!!! - though I'd be watching the first several days...looks like heavy water & the Big Stick
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Quoting StormW:


Well, I've always had a theory...Hurricanes do not go to school, and do not care about Calculus, and Differential Equations, and don't read computer model guidance outputs.


quote of the year!
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YES and just in time for the weekend it looks like
won't be nearly as good here, and we'll still be dodging tourons and university freshmen.

P.R. with the win
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500 mbr winds
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Post 779 surfmom, Puerto Rico is an awesome place for a surf trip, Went to Rincon for two weeks and almost decided to sell all my things in the states and stay there.
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Quoting pilotguy1:


Everything I have seen from every source does not indicate anything stronger than a cat 1.


Its reorganizing it wont take much to get back to a cat 2 again or higher. Look at yesterday. It went from TS to cat 2 hurricane in one day.
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Quoting mydiapersarefull:
Hurricane Danielle Surf Forecast for Puerto Rico

the place to be...need ticket and vacation time!

YES and just in time for the weekend it looks like
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788. xcool
Danielle MOVE WNW off forecast points..
Member Since: September 26, 2009 Posts: 2 Comments: 15684
looks like STORM IS RIGHT AGIAN NHC is gonna have to shift left
http://www.wunderground.com/tropical/tracking/at201006_model.html
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PR is pretty flat right now...


And Dont I know it :(
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Hurricane Danielle Surf Forecast for Puerto Rico

the place to be...need ticket and vacation time!
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looks like the models are seeing a building high pressure system in the atlantic? That is a major shift in thinking for 96L from yesterday.

However, as we all have learned from Storm, do not only follow the models.

we will see. should be interesting!!
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Wow a big shift

sorry image button not working


https://my.sfwmd.gov/sfwmd/common/images/weather/plots/storm_96.gif

and earler today

http://moe.met.fsu.edu/~acevans/models/archive/2010/al962010/al962010_2010082400.png
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Storm. Some interesting curvature of the storms off and on the NC coast, and pressures already sub 1010mb. Thoughts?
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RE-FRESH RE-FRESH RE-FRESH TIME!!!!

Pouring here in SRQ - Surf is Up - Weather Report
from a Surfers Perspective - AURASURF/MICAH WEAVER

We got waves. Buoys are picking up and there some choppy waves from the SW at the beach now. Expect building surf today with leftovers for Wednesday. Watch out for flooded streets. 3.5 inches of rain have fallen in St Pete during the last 36hrs. have fun. If you get back from the beach you can post a report in the comments. I should have an update later in the form of a tweet at the bottom of this page.
Tuesday: waist high and choppy, a chest high choppy peak possible at best spots this afternoon. Wednesday: Knee to occ waist high choppy leftovers.
Hurricane Danielle Surf Forecast for Puerto Rico: Danielle is going to blow up the ATL. Not only will she bring her own swell but the gradient squeeze between her and the high will light up 1000's of miles of open ocean and send a solid NE swell to the Bahamas, Florida, the Caribbean and PR. PR is pretty flat right now. The first bit of powerful ENE swell will hit Friday am. Looks chest to head high in Isabela and waist to chest down in Rincón. Saturday more swell fills in. Chest to head high in Rincón but head high plus on the the N Coast all this meeting light E trades. Sunday the swell peaks, double overhead at Middles and head high to 2' overhead around the corner in Rincón. The swell stays solid on Monday, still head high plus with SE trades and then finally dropping on Tuesday, waist to chest high with SE winds. Looks like a really fun swell pa' la isla entera.
GULF OF MEXICO - swfl - Rain & Chunk Waves

photo - Gulfster
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I'm in Houston and as long as it isn't too powerful, I would welcome a tropical system. We need rain! We have had tons of storms in the area, but none here.
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looks like STORM IS RIGHT AGIAN nhc is gonna have to shift left
http://www.wunderground.com/tropical/tracking/at201006_model.html
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Storm,

Two quick questions. First, when do you see this Low exiting Florida and returning to sunny skies?

Second (because I do not have access to the NAO charts), have they shifted negative or positive for September? Just wondering because I keep hearing of a building high pressure system

thanks
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769. Relix


Nice model shift there. Closer to putting the islands at risk now.
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Last night at 11pm they forecasted Danielle to be at 18.3N 47.5W at 11pm tonight

well Danielle is passed 47.5N and just reached 17N, so Danielle is further south than what they forecasted last night

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Quoting btwntx08:
oh the cmc shows something in houston on saturda im headed there on that day


Well I'll be here. :)
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Blog is eating my posts. Anyways, some low pressure here in eastern NC. New Bern around 1010 and MHC @ 1009.5. Raining cats and dogs, too.
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Quoting btwntx08:
txhurricane look at post 727 as well


yeah, I saw that too. How accurate are these models?
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764. srada
Quoting xcool:
SOUTHEAST/EAST COAST...
A VARIETY OF SOLUTIONS REMAIN IN REGARDS TO THE EVOLUTION OF A
POSSIBLE UPPER LOW ROUNDING THE SOUTHEAST SIDE OF THE EASTERN
RIDGE BY NEXT TUESDAY... WITH THE GFS STRONGEST JUST OFF THE
SOUTHEAST COAST AND ECMWF RUNS STRONGEST OVER/NEAR THE LOWER
MISSISSIPPI VALLEY. THE GEFS MEAN REPRESENTS BOTH AREAS TO SOME
DEGREE WHILE THE 12Z ECMWF MEAN IS NOT ENTHUSIASTIC ABOUT EITHER
AREA... SUPPORTING A COMPROMISE APPROACH FOR NOW. A SMALL
PERCENTAGE OF THE 00Z MULTI-MODEL ENSEMBLE MEMBERS USE THIS UPPER
LOW TO SWING HURRICANE DANIELLE TOWARDS THE
CAROLINAS/MID-ATLANTIC/NEW ENGLAND COASTS IN 7-10 DAYS. EVERY
COUPLE YEARS THE ENSEMBLE GUIDANCE /OR THE DETERMINISTIC CANADIAN
GLOBAL MODEL/ TRIES TO ANOMALOUSLY TURN/STAIR-STEP A RECURVING
SYSTEM WESTWARD TOWARDS THE NORTHEASTERN UNITED STATES. BELIEVE
DANIELLE IS TOO FAR GONE INTO THE RECURVATURE PROCESS AROUND THE
SUBTROPICAL RIDGE TO ITS EAST AND THAT THE UPPER LOW WHICH FORMS
NEAR THE SOUTHEAST SHOULD BE TOO FAR AWAY FROM DANIELLE TO TURN
THE STORM BACK TOWARDS THE EAST COAST. DANIELLE...AMONG OTHER
SYSTEMS...WILL BE COORDINATED WITH NHC AT 16Z TODAY

HPC


WOW!!!!!!!!!!
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Quoting DestinJeff:




Jeff - anything for not-yet-earl? I'm getting concerned about my upcoming bahamas trip. thx.
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We are going tru a textbook negative NAO. This explains for the dry air over the south easter US and the weak high over the N Atlantic. Unless we enter a positive NAO soon expect all of these systems to be fish storms.
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Quoting StormW:


No way!
LOL!!

Just want to add that I appreciate and respect your input whether it differs from, or is in agreement with, the official forecast. You support your opinions with evidence set forth in a clear and logical manner. Whether you are right or wrong at the end of the day, reading opposing viewpoints makes me think and question, and that's how a person learns. Why have a blog that discourages differing viewpoints from people who clearly understand what they're talking about?

And, looking at the historical track on Danielle...it looks a lot more like the track you've been describing than any forecast track I recall seeing so far.

JMO
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Quoting jason2010xxxx:
WOW


Thank you, Jason.
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The discussion at 11pm on Sunday night had Danielle at 18.5N 46.2W by 11pm tonight

Look where she is now, quite a bit south and west of that location
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754. xcool
possible home brew ..stay tuned
Member Since: September 26, 2009 Posts: 2 Comments: 15684
1st) An apology for sending you to the wrong NHC-ATCF page.
Came from 'copy&paste'ing and forgetting to check my links.
The problem has been corrected.

HurricaneDanielle's heading has turned westward to 5.1degrees north of WestNorthWest from the previous 8.4degrees west of NorthWest
23Aug - 06pmGMT - 15.2n40.7w - - 65knots . . . . 987mb - NHC-ATCF *
TS.Danielle upgraded to H.Danielle
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
H.Daniel 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
85knots=~97.8mph _ _ _ ~87knots=100mph _ _ _
75knots=~86.3mph _ _ _ ~69.6knots=80mph _ _ _ 65knots=~74.8mph
NHC rounds windspeeds to the nearest 5mph or to the nearest 5knots

* Before NHC reevaluated&altered TS.Danielle's path:
23Aug - 06pmGMT was 60knots , 991mb

Copy&paste 15.7n44.0w-15.9n44.6w, 15.9n44.6w-16.1n45.8w, 16.1n45.8w-16.6n46.5w, 16.6n46.5w-17.1n47.5w, bda, nas into the GreatCircleMapper for a look at the last 12hours.
Member Since: August 21, 2007 Posts: 0 Comments: 4860
Morehead City down to 1009.5
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AL, 06, 201008241745, 10, DVTS, CI, , 1700N, 4740W, , 2, 90, 2, , , , , , , , , , , , , , , , , , TAFB, MN, VI, 3, 4550 /////, , , MET8, CSC, T, DT = 4.5 BASED ON CENTER EMBEDDED IN LG. NLINEADT
AL, 06, 201008241745, 10, DVTS, CI, , 1710N, 4750W, , 2, 65, 2, , , , , , , , , , , , , , , , , L, SAB, SE, VI, 3, 3040 /////, , , , LLCC, T, DT=2.5 BO CBND MET=3.0 PT=3.0 FTBO MET PA=20 NMI

CI# /Pressure/ Vmax
4.3 / 984.4mb/ 72.2kt


Final T# Adj T# Raw T#
3.6 3.6 3.0

Fair bit of difference on the (A)DTs, as you might expect.
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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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