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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Nice burst with 96L

""
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2647. xcool


UPDATEE
Member Since: September 26, 2009 Posts: 2 Comments: 15684
2646. xcool


TD OR TS IN GOM
Member Since: September 26, 2009 Posts: 2 Comments: 15684
GFS is showing a pattern change in the extended outlook that should keep waves moving more W. The HP off the EC is expected to get stronger and move more E and links up with the Bermuda HP. September should be a crazy month if that verifies.
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2644. JLPR2
Quoting xcool:


falling apart again
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2642. xcool
SHE NOT MOVE MUCH .
Member Since: September 26, 2009 Posts: 2 Comments: 15684
2641. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15684
2640. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15684
HP never bridges the gap just like the GFS shows. If that were to change then things could get interesting.
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Quoting robert88:
The reason 96L is fishing is because of the weakness left behind from Danielle. Any slowing down with Danielle takes everything else out to sea.


That's a possibility.
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The reason 96L is fishing is because of the weakness left behind from Danielle. Any slowing down with Danielle takes everything else out to sea.
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2636. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15684
2634. xcool
LOL ecmwf
Member Since: September 26, 2009 Posts: 2 Comments: 15684
TropicalStormDanielle's heading has turned northward to 9.5degrees north of NorthNorthWest
from the previous heading of 1.7degrees north of WestNorthWest.

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
25Aug - 12amGMT - 17.9n49.1w - - 65knots . . . . 990mb - NHC-ATCF
TS.Danielle becomes H.Danielle again
25Aug - 03amGMT - 18.2n49.8w - - 75mph . . . . . 990mb - NHC.Adv.14
25Aug - 06amGMT - 18.5n50.3w - - 75knots . . . . 990mb - NHC-ATCF

_ _ _ 65knots=~74.8mph _ _ _ ~65.2knots=75mph _ _ _ 75knots=~86.3mph
NHC rounds windspeeds to the nearest 5mph or to the nearest 5knots

Copy&paste 16.6n46.5w, 17.1n47.5w-17.5n48.2w, 17.5n48.2w-17.9n49.1w, 17.9n49.1w-18.2n49.8w, 18.2n49.8w-18.5n50.3w, bda, jax into the GreatCircleMapper for a look at the last 12hours.
Member Since: August 21, 2007 Posts: 0 Comments: 4860
2631. xcool
AL, 06, 2010082506, , BEST, 0, 185N, 503W, 75, 982,
Member Since: September 26, 2009 Posts: 2 Comments: 15684
2629. xcool
ecmwf 96L OUTT SEA
Member Since: September 26, 2009 Posts: 2 Comments: 15684
HPC says just about the opposite

.EVOLUTION OVER/NEAR THE NRN AND WRN GULF OF MEXICO...

PREFERENCE: BLEND AMONG GFS/ECMWF AND 21Z SREF/00Z GEFS MEANS

EACH MODEL HAS SLIGHTLY DIFFERENT EMPHASIS OF MID LVL IMPULSES
ACROSS THE WRN/NRN GULF AND VICINITY. HOWEVER A COMPARISON OF THE
NAM/GFS/ECMWF/UKMET/CANADIAN GLBL AND ENSEMBLE GUIDANCE REVEALS A
ROBUST CONSENSUS THAT IS WEAKER THAN THE NAM WITH THE BROAD AREA
OF SFC LOW PRESSURE OVER THE WRN GULF. THIS DOMINANT CLUSTER ALSO
DOES NOT BRING LOW PRESSURE AS FAR NWD/NWWD AS THE NAM LATE IN THE
FCST. THE NAM HAS HAD A PRONOUNCED STRONG BIAS WITH PREDICTED
FEATURES OVER THE GULF REGION THIS SEASON SO THE NON-NAM CONSENSUS
APPEARS TO BE THE MOST LIKELY SCENARIO. PREFER A BLEND AMONG THE
GFS/ECMWF AND 21Z SREF/00Z GEFS MEANS TO RESOLVE DETAIL DIFFS
AMONG NON-NAM SOLNS.
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2626. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Quoting btwntx08:
96 hr ecmwf bombs danielle just se of berumda


Not a pretty picture.
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Part of a q&a with KFDM met on another site. about the disturbance in the gulf. Link

Low to far south on the GFS in my opinion. We'll see though. Sure not going to shift South Saturday with weakness to the north at 500. This new GFS is about as bad as the old one.

Even if this does develop, I don't see it becoming very strong. Maybe a weak to moderate TS.
Hope so, but winds aloft are favorable by late Wed. plus it will be over Water a while
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.
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2621. leo305
I dont think conditions are favorable for Danielle to gain too much strength..
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Quoting smuldy:
no no not knocking you at all thats a good guess this far out agreed i'm just saying there is no way for anyone to know with any decent certainty yet which I think is what you were saying too lol


Yeah pretty much.
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2619. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Quoting traumaboyy:


Work it on over here....we got an old trailer on our property....I am going to push it over with my tractor and call the news crews....mom in green moo-moo and curlers....I think we could make a spot on Storm Stories Think it would work??


LOL

Go for it.
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2616. HadesGodWyvern (Mod)


so close to land..
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2615. xcool
she slowdown.
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2614. smuldy
Quoting KoritheMan:


Yep. I'm not as certain in my forecast for 96/Earl as I sound. Trust me.
no no not knocking you at all thats a good guess this far out agreed i'm just saying there is no way for anyone to know with any decent certainty yet which I think is what you were saying too lol
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2613. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15684
2612. mbjjm
All the models take Earl out to sea,but there is the possibility Earl could sneak underneath the trough and then being pushed further west by a building ridge of high pressure.
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Quoting KoritheMan:


HEY! I resent that! :(

hahaha

In all seriousness, though. I think 96L is a long-range threat to the east coast, from North Carolina to Florida. Hard to delineate a specific threat area, though.


Work it on over here....we got an old trailer on our property....I am going to push it over with my tractor and call the news crews....mom in green moo-moo and curlers....I think we could make a spot on Storm Stories Think it would work??
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Quoting smuldy:
agreed-until Danielle turns and the synoptic patter behind her settles into its framework that future Earl will be dealing with you would have a better chance of nailing down the Super Bowl winner than the spot this storm will be 8 days from now.


Yep. I'm not as certain in my forecast for 96/Earl as I sound. Trust me.
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2609. smuldy
Quoting KoritheMan:


HEY! I resent that! :(

hahaha

In all seriousness, though. I think 96L is a long-range threat to the east coast, from North Carolina to Florida. Hard to delineate a specific threat area, though.
agreed-until Danielle turns and the synoptic pattern behind her settles into its framework that future Earl will be dealing with you would have a better chance of nailing down the Super Bowl winner than the spot this storm will be 8 days from now.
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2608. mbjjm
ADT Satellite Intensity estimate

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2607. markot
earl wont go out to sea. a large high pressure ridge will build in the atlantic....
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2606. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15684
2605. mbjjm
Quoting KoritheMan:


Aren't those statistical models? They always seem to be vastly inaccurate in comparison to the dynamical models, which aren't foreseeing recurvature (save, of course, the poleward biased GFS).

I'm not wishcasting at all. I just forecast. And right now, I don't see 96L/Earl recurving. But you're right. It's uncertain.


Those are all the models dynamic, consensus and statistical
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Quoting traumaboyy:


Wassup Kori....where are you wishcasting this interesting storm to??


HEY! I resent that! :(

hahaha

In all seriousness, though. I think 96L is a long-range threat to the east coast, from North Carolina to Florida. Hard to delineate a specific threat area, though.
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Quoting smuldy:
meant most realistic of the hopeful scenarios, as in i doubt this will be a TS if/when it gets there; if i had to make a call (guess i might as well) i would say moderate cat2, it is still running ahead of itself too quickly to gain major status before it turns, imo


In that case, I agree.
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Quoting KoritheMan:


Aren't those statistical models? They always seem to be vastly inaccurate in comparison to the dynamical models, which aren't foreseeing recurvature (save, of course, the poleward biased GFS).

I'm not wishcasting at all. I just forecast. And right now, I don't see 96L/Earl recurving. But you're right. It's uncertain.

Wassup Kori....where are you wishcasting this interesting storm to??
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2601. smuldy
Quoting KoritheMan:


Not really.
meant most realistic of the hopeful scenarios, as in i doubt this will be a TS if/when it gets there; if i had to make a call (guess i might as well) i would say moderate cat2, it is still running ahead of itself too quickly to gain major status before it turns, imo
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2600. HadesGodWyvern (Mod)
Joint Typhoon Warning Center
Tropical Disturbance Summary
06:00 AM UTC August 25 2010
=========================================

An area of convection (97W) located at 19.5N 140.0E or 420 NM northwest of Saipan. Animated water vapor satellite imagery shows deep convection developing near a weak low level circulation center. This disturbance lies in an area of low vertical wind shear beneath an upper level anticyclone. Tropical Upper Tropospheric Trough cells located to the northwest and east are favorably enhancing upper level outflow.

Maximum sustained winds near the center is 10-15 knots with a minimum sea level pressure of 1008 MB.
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Anyone else notice the spread in the intensity models to the end of the forecast period for Invest 96? Some hinting at major hurricane, others low end TS. Interesting to have such divergence.
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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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