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Atlantic Disturbance 96L Still 96L But Threat to US Increases

By: Dr. Jeff Masters , 3:41 PM GMT on August 23, 2014

(By Steve Gregory - Substituting for Dr. Masters who is on Vacation.)

There’s been little change overnight in 96L, with RECON reports indicating a broad, disorganized circulation center with a surface pressure near 1007mb along the north coast of Hispaniola near 20.8N/71.7W. Mid-upper level winds also indicate that the larger scale circulation field was not significantly impacted by the mountainous terrain of Hispaniola, and has been moving on a generally West/West-Northwest course at around 20Kts, though a somewhat more Northwesterly (310°) heading seems to have developed over the last few hours. Although there continues to be large scale outflow associated with the high level anti-cyclone sitting atop the developing system,, there are no distinct outflow channel jets; so any initial intensification of the system later today or on Sunday will likely start out on the slow side. While wind shear of 15-20Kts continues to be of moderate intensity across large areas of the system’s structure, an area of lighter shear (<10Kts) close to the circulation center continues to move in tandem with the systems primary circulatory vortex.

The overall satellite signature continues to slowly improve, with a somewhat more symmetrical appearance, and large scale curvature especially noteworthy in the E-SE quadrant where hints of a ‘feeder’ band type structure appears to be developing.

With the system embedded in a moist environment and no significantly drier air noted on the periphery of the system, dry air should not be a hindrance to intensification during the next 48 hours. In addition, the developing system is, or soon will be, moving over very warm waters, with SST’s over 29°C (~85°F) – well above that needed to support hurricane intensities. However, if the system should slow to a crawl or even go stationary later Sunday as forecast by many models, upwelling of cooler sub-surface waters could prove significant, slowing the rate of intensification appreciably.

Since yesterday, there have been major shifts to the forecast tracks – especially after Sunday – raising the risk level for the entire eastern US from Florida to New England – with about equal odds that the potential storm will impact the coast or turn out to sea. This is not a surprise since track and intensity forecasts are notorious for major shifts for systems that are still in the formative stages. Ironically, the CMC forecast, which was consistently forecasting the system to track across south Florida, has now shifted dramatically to that shown by many of the major model suites, while the more reliable track forecast models have now shifted westward, much closer to the coast. The spread of forecast tracks is now quite large – again, a typical feature of forecasts for systems still forming. The forecast challenge has been unusually high for this system, not just because it has yet to really develop and has tracked across Hispaniola (a landmass notorious for ‘destroying’ even the most well developed and intense hurricanes) but because of the unusually high track sensitivity to a ‘weakness’ in the east-west sub-tropical ridgeline that extends from the central Atlantic to the Gulf coast. While the models continue to show a break between the high pressure center in the central Atlantic and the one near the Gulf coast during the next 36 hours, the resulting TROF within this break will be relatively weak, and will begin to dissipate staring late Monday. The exact timing of this ‘break’ – and the exact location and strength of 96L during the next 72 hours will determine exactly where and when (if ?) the system turns northward. Prior model runs were in generally good agreement that the system would turn northward when it was still about 300NM east of Florida, while the most recent model runs show a far more gradual recurvature – with some of the more reliable models showing the storm getting very close to the coast before beginning to turn northward, and are all calling for the storm to be moving much slower, with the system not expected to be near the US coast for another 4 or even 5 days.

The intensity forecasts are equally difficult, although they have continued to be quite consistent with each other and between succeeding model runs. The odds are relatively high (70%-80%) the system will become a tropical storm either late today or on Sunday, with a fairly slow rate of intensification to near CAT 1 intensity on Monday or Tuesday. This continues to be a reasonably good forecast scenario all things considered, and a CAT 1 intensity threat for the east coast of Florida northward to the Carolinas is quite real – albeit a still very uncertain one.

All things considered, I must admit this is one of the more ‘challenging’ forecasts I’ve come across in my many decades of forecasting.



Fig 1: Early morning VIS imagery shows a system still trying to get ‘its act together’ with a better organized signature than yesterday, but a still poorly organized low level circulation. Some hints of ‘feeder’ type bands are seen extending into the southern CARIB south and east of the ‘center’ witch should provide an ample flow of moisture into the system assuming it finally intensifies into a strong cyclone.



Fig 2: The Total Precipitable water (TPW) analysis show 96L surrounded by moist air, with a deep moisture plume extending from the deep tropics over northern SOAMER across the CARIB into the mid-level vortex circulation that is 96L. This should continue to supply high atmospheric moisture content to the system as it develops during the next few days.



Fig 3: Wind Shear analysis (mid levels) shows moderate shear conditions in the 15-20Kt range in the vicinity of the primary low-mid level circulation. Much lower shear conditions are seen just south-southwest of the mid level circulation field. The shear analysis is automated, so the lower values shown may not be very precise in the delineation of its aerial extent. However, this wind shear ‘couplet’ has been moving in tandem with the disturbance, and since none of the models are forecasting adverse shear conditions ahead of the systems’ projected track – shear should not be a major hindrance to intensification for the next 72 hours.



Fig 4: There’s been no significant change to yesterday’s development of a high level (~200mb) anti-cyclone which is providing decent outflow for the developing system. Though no distinct outflow jet channels have developed, the current level of outflow does support a CAT 1 intensity storm.



Fig 5: The lower level steering winds clearly show the east-west orientated sub-tropical ridge from the central Atlantic westward to the Gulf coast region, along with a break (TROF) between the two separate High pressure centers. This TROF / Ridge-line is the primary feature set that will ultimately determine the track taken by the developing cyclone. Both the intensity of the developing system and the exact location and impact of the TROF on the sub-tropical ridge will determine how the steering currents evolve and ultimately guide the the cyclone over the next several days. If the TROF weakens quickly enough, allowing the ridge to rebuild westward into the SE US – the cyclone will track into the SE coast of the US. If the TROF/ridge weakness remains in place – the cyclone will recurve and turn northward before reaching the coast.



Fig 6: Early cycle model runs are in general agreement on the track of the developing cyclone for the next 36-48 hours, but the spread between solutions beyond then has grown quite large since yesterday; indicative of the difficulty the models are having in determining the subtle-changes and inter-play between the sub-tropical ridge, the TROF off the east coast, and the cyclone itself.



Fig 7: Intensity forecasts have been fairly consistent over the past few days - seemingly unaffected by the track changes - with slow intensification expected during the next 72 hrs to CAT 1 Hurricane force by early next week.

I’ll have another brief update late this afternoon after additional RECON and SAT imagery can be reviewed, along with all the 12Z global model run output.

Steve


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

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924. TheEyeiscalm
4:03 PM GMT on August 27, 2014
Hi all nice to meet you.




Andrew, Wilma, Katrina, Charley,Georges
Member Since: December 31, 1969 Posts: Comments:
923. Thunderground
10:59 PM GMT on August 23, 2014
TGIOTS
Member Since: December 31, 1969 Posts: Comments:
922. hydrus
9:16 PM GMT on August 23, 2014
It is only my opinion, but this will fill in rather quickly, and may get a name this evening or tomorrow morning.



Member Since: December 31, 1969 Posts: Comments:
921. win1gamegiantsplease
9:05 PM GMT on August 23, 2014
Quoting 917. overwash12:

There is no reason this can not get to cat #3 by Monday,Heading straight for The OBX of North Carolina!


Too early.
Member Since: December 31, 1969 Posts: Comments:
920. JRRP
9:04 PM GMT on August 23, 2014
What the ....
Member Since: December 31, 1969 Posts: Comments:
919. Hurricane1956
9:03 PM GMT on August 23, 2014
Hello, well it's over!!! for South Florida,thanks God!!!!, this thing is moving out to sea!!. I have great confidence in the NHC track,they have 2 planes in there mapping all weather conditions,so they know much better than all of us here in the blog.
Even though still puzzling that some of the reliable models take this depression much more West toward Florida? or just clipping the coast, again the experts at the NHC better know what they are doing!!,because this system is very close to the South East coast of the USA.
Member Since: December 31, 1969 Posts: Comments:
918. Barefootontherocks
8:58 PM GMT on August 23, 2014
Quoting 882. aquak9:

oh dear-
now what?
Spam and yogurt?
Member Since: December 31, 1969 Posts: Comments:
917. overwash12
8:54 PM GMT on August 23, 2014
There is no reason this can not get to cat #3 by Monday,Heading straight for The OBX of North Carolina!
Member Since: December 31, 1969 Posts: Comments:
916. hurricanewatcher61
8:53 PM GMT on August 23, 2014
So it is OTS now? WOW!
Member Since: December 31, 1969 Posts: Comments:
915. Sfloridacat5
8:53 PM GMT on August 23, 2014
It's hard to believe that 96L traveled all the way from Africa across the Atlantic to make a turn right before it gets to Florida. It's pretty amazing.
Another chance for the Outerbanks to see a hurricane. It just might end up being their season.
Member Since: December 31, 1969 Posts: Comments:
914. Grothar
8:53 PM GMT on August 23, 2014
Quoting 895. Drakoen:

I think the track should have been farther west to include portions of eastern Florida but it's no surprise they went with the consensus track.


They might later.

Member Since: December 31, 1969 Posts: Comments:
913. VegasRain
8:52 PM GMT on August 23, 2014
Quoting 889. BahaHurican:

Before I go....




IDK... I'm not convinced that the recurve will occur when predicted. I think this system may come closer to the Carolina's than the official forecast is calling for. That slowdown at 48 hours may not be as slow as the models are predicting and it may move much closer to the mainland before it starts to move to the North and then the NNW.
Member Since: December 31, 1969 Posts: Comments:
911. muddertracker
8:51 PM GMT on August 23, 2014
Quoting 865. CybrTeddy:

Looks like a recurve.




Trusting the trof, eh? Alrighty then.
Member Since: December 31, 1969 Posts: Comments:
910. washingaway
8:51 PM GMT on August 23, 2014
The ULL bookin it thru the Florida Straits could helpful before long.

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909. tropicfreak
8:51 PM GMT on August 23, 2014
Quoting 865. CybrTeddy:

Looks like a recurve.





Very wide cone though.
Member Since: December 31, 1969 Posts: Comments:
908. cappyric
8:50 PM GMT on August 23, 2014
Things getting a bit more active in the central Exumas.
Squalls and shifting winds.
Member Since: December 31, 1969 Posts: Comments:
907. SPLbeater
8:49 PM GMT on August 23, 2014
Quoting 808. louisianaboy444:

Have noticed something in the models and pattern that may or may not be significant. With high pressure over the northeastern portions of the U.S. and a developing low pressure area across the Bahamas, this would make for a classic Cold Air Damming scenario across the eastern side of the Appalachian Mountains. Question is, are the models seeing this and how would it affect the mid-level steering? I know cold-air damming is usually a surface event, but wouldn't the cold air lower mid-level heights, which could cause a weakening of the ridge over the central U.S.? This could be why some models move the storm northwestward into the southeastern United States.


My NWS from Raleigh has made no mention of a summertime cold air damming event, with temps dropping about 5-7 degrees below normal...However, the NWS from Blacksburg, VA began their short term discussion by saying that 'a strong wedge of high pressure will be over the forecast area' through Tuesday. Resembles a CAD if you ask me. I can't draw any conclusion from that...but if you can, you got more than me. :)
Member Since: December 31, 1969 Posts: Comments:
906. TimSoCal
8:49 PM GMT on August 23, 2014
Marie's eye is trying to clear out.

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905. Maineweatherguy20023
8:49 PM GMT on August 23, 2014
TD 4! Now the blog can explode with 2300 copies of the same image of the 5 day forecast cone! Whopee!
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904. LargoFl
8:49 PM GMT on August 23, 2014
Member Since: December 31, 1969 Posts: Comments:
903. A4Guy
8:49 PM GMT on August 23, 2014
Hate to say it, but I bet when that cone came out, several WU blog commenters shed a few tears.
Member Since: December 31, 1969 Posts: Comments:
902. WunderAlertBot (Admin)
8:48 PM GMT on August 23, 2014
JeffMasters has created a new entry.
901. SLU
8:48 PM GMT on August 23, 2014
OUTLOOK VALID 28/1800Z 32.0N 76.5W
MAX WIND 70 KT...GUSTS 85 KT.
Member Since: December 31, 1969 Posts: Comments:
900. LargoFl
8:47 PM GMT on August 23, 2014
TD-4 ..now how long before the models get the new info into their runs...tonight or 6Z tomorrow?
Member Since: December 31, 1969 Posts: Comments:
899. JNFlori30A
8:47 PM GMT on August 23, 2014
Quoting 806. aquak9:


I opened the lid to my washing machine and they named it-
nice...
Member Since: December 31, 1969 Posts: Comments:
898. wunderweatherman123
8:47 PM GMT on August 23, 2014
Quoting 865. CybrTeddy:

Looks like a recurve.


remember debby's track? into texas. day later switched into florida. it happens
Member Since: December 31, 1969 Posts: Comments:
897. Envoirment
8:47 PM GMT on August 23, 2014
Quoting 865. CybrTeddy:

Looks like a recurve.




Nice to have an official NHC forecast at last. I can't load the NHC website for some reason, so thanks for posting this (maybe WU crashed it lol).
Member Since: December 31, 1969 Posts: Comments:
896. SLU
8:47 PM GMT on August 23, 2014
04L

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895. Drakoen
8:46 PM GMT on August 23, 2014
I think the track should have been farther west to include portions of eastern Florida but it's no surprise they went with the consensus track.
Member Since: December 31, 1969 Posts: Comments:
894. ScooterXX7
8:46 PM GMT on August 23, 2014
It really feels like the OBX are always at risk moreso than S. FL or NOLA.
Member Since: December 31, 1969 Posts: Comments:
893. congaline
8:46 PM GMT on August 23, 2014
If NHC says its moving NW then I guess it is, tho it appears to me to still be moving WNW. Glad its finally been classified a Depression...
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892. FOREX
8:45 PM GMT on August 23, 2014
Quoting 866. washingaway:

If there was conference call it probably to discuss who was going to make the official track. Any takers?
SAR
Member Since: December 31, 1969 Posts: Comments:
891. 2010hurricane
8:45 PM GMT on August 23, 2014
We have TD 4Link
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890. Sfloridacat5
8:45 PM GMT on August 23, 2014
Florida is just out of the cone.
Member Since: December 31, 1969 Posts: Comments:
889. BahaHurican
8:45 PM GMT on August 23, 2014
Before I go....

Member Since: December 31, 1969 Posts: Comments:
888. JrWeathermanFL
8:45 PM GMT on August 23, 2014


notDOOM..??
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887. LargoFl
8:45 PM GMT on August 23, 2014
18Z Nam 75% finished.......................................... ............................................
Member Since: December 31, 1969 Posts: Comments:
886. cyclanaq
8:45 PM GMT on August 23, 2014
With all the convection starting to blossom to the north and east of the weak center, it may induce formation of a new center further N or NE, which would then make it more likely to head out to sea.
Member Since: December 31, 1969 Posts: Comments:
885. FOREX
8:46 PM GMT on August 23, 2014
Quoting 865. CybrTeddy:

Looks like a recurve.




No Gulf, not even close.
Member Since: December 31, 1969 Posts: Comments:
884. PalmBeachWeatherBoy
8:45 PM GMT on August 23, 2014
Are fish land-casters? hmmm, maybe they are tired of all these storms. Lol, just some humor to lighten the mood.
Member Since: December 31, 1969 Posts: Comments:
883. KEEPEROFTHEGATE (Mod)
8:44 PM GMT on August 23, 2014
000
WTNT24 KNHC 232040
TCMAT4

TROPICAL DEPRESSION FOUR FORECAST/ADVISORY NUMBER 1
NWS NATIONAL HURRICANE CENTER MIAMI FL AL042014
2100 UTC SAT AUG 23 2014

CHANGES IN WATCHES AND WARNINGS WITH THIS ADVISORY...

THE GOVERNMENT OF THE BAHAMAS HAS ISSUED A TROPICAL STORM WARNING
FOR THE SOUTHEASTERN BAHAMAS...INCLUDING THE ACKLINS...CROOKED
ISLAND...LONG CAY...THE INAGUAS...MAYAGUANA...AND THE RAGGED
ISLANDS...AS WELL AS FOR THE TURKS AND CAICOS ISLANDS...AND FOR THE
CENTRAL BAHAMAS...INCLUDING CAT ISLAND...THE EXUMAS...LONG
ISLAND...RUM CAY...AND SAN SALVADOR.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* SOUTHEASTERN BAHAMAS...INCLUDING THE ACKLINS...CROOKED
ISLAND...LONG CAY...THE INAGUAS...MAYAGUANA...AND THE RAGGED
ISLANDS...AS WELL AS FOR THE TURKS AND CAICOS ISLANDS
* CENTRAL BAHAMAS...INCLUDING CAT ISLAND...THE EXUMAS...LONG
ISLAND...RUM CAY...AND SAN SALVADOR

A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA...IN THIS CASE WITHIN
THE NEXT 24 HOURS.

INTERESTS IN THE NORTHWESTERN BAHAMAS SHOULD MONITOR THE PROGRESS
OF THIS SYSTEM.

TROPICAL DEPRESSION CENTER LOCATED NEAR 21.8N 72.3W AT 23/2100Z
POSITION ACCURATE WITHIN 20 NM

PRESENT MOVEMENT TOWARD THE NORTHWEST OR 310 DEGREES AT 10 KT

ESTIMATED MINIMUM CENTRAL PRESSURE 1005 MB
MAX SUSTAINED WINDS 30 KT WITH GUSTS TO 40 KT.
WINDS AND SEAS VARY GREATLY IN EACH QUADRANT. RADII IN NAUTICAL
MILES ARE THE LARGEST RADII EXPECTED ANYWHERE IN THAT QUADRANT.

REPEAT...CENTER LOCATED NEAR 21.8N 72.3W AT 23/2100Z
AT 23/1800Z CENTER WAS LOCATED NEAR 21.5N 72.2W

FORECAST VALID 24/0600Z 22.9N 73.6W
MAX WIND 35 KT...GUSTS 45 KT.
34 KT... 40NE 0SE 0SW 0NW.

FORECAST VALID 24/1800Z 24.0N 74.4W
MAX WIND 40 KT...GUSTS 50 KT.
34 KT... 50NE 50SE 20SW 30NW.

FORECAST VALID 25/0600Z 24.6N 74.8W
MAX WIND 45 KT...GUSTS 55 KT.
34 KT... 60NE 50SE 30SW 60NW.

FORECAST VALID 25/1800Z 25.0N 75.0W
MAX WIND 55 KT...GUSTS 65 KT.
50 KT... 40NE 30SE 20SW 30NW.
34 KT... 80NE 70SE 50SW 60NW.

FORECAST VALID 26/1800Z 26.5N 76.0W
MAX WIND 65 KT...GUSTS 80 KT.
50 KT... 50NE 50SE 30SW 40NW.
34 KT...110NE 100SE 70SW 90NW.

EXTENDED OUTLOOK. NOTE...ERRORS FOR TRACK HAVE AVERAGED NEAR 150 NM
ON DAY 4 AND 200 NM ON DAY 5...AND FOR INTENSITY NEAR 15 KT EACH DAY

OUTLOOK VALID 27/1800Z 29.0N 77.5W
MAX WIND 65 KT...GUSTS 80 KT.

OUTLOOK VALID 28/1800Z 32.0N 76.5W
MAX WIND 70 KT...GUSTS 85 KT.

REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 21.8N 72.3W

NEXT ADVISORY AT 24/0300Z

$$
FORECASTER BRENNAN



Member Since: December 31, 1969 Posts: Comments:
882. aquak9
8:44 PM GMT on August 23, 2014
oh dear-
now what?
Member Since: December 31, 1969 Posts: Comments:
881. hurricane23
8:44 PM GMT on August 23, 2014
Track away from fl possible threat to NC.
Member Since: December 31, 1969 Posts: Comments:
880. WeatherNerdPR
8:44 PM GMT on August 23, 2014
Member Since: December 31, 1969 Posts: Comments:
879. BahaHurican
8:44 PM GMT on August 23, 2014
Well, not surprised to see that Advisory. Now to see how quickly they upgrade to Cristobal....

BBL.
Member Since: December 31, 1969 Posts: Comments:
878. Climate175
8:44 PM GMT on August 23, 2014
Member Since: December 31, 1969 Posts: Comments:
877. Ameister12
8:44 PM GMT on August 23, 2014
Buckle your seat belts! The blog is going into ludicrous speed.
Member Since: December 31, 1969 Posts: Comments:
876. VegasRain
8:44 PM GMT on August 23, 2014
Quoting 850. CybrTeddy:

Boom. TD4 on the NHC site.


Thar the blows..
Member Since: December 31, 1969 Posts: Comments:
875. Climate175
8:47 PM GMT on August 23, 2014
Member Since: December 31, 1969 Posts: Comments:
874. wunderweatherman123
8:43 PM GMT on August 23, 2014
Quoting 862. CybrTeddy:

000
WTNT24 KNHC 232040
TCMAT4

TROPICAL DEPRESSION FOUR FORECAST/ADVISORY NUMBER 1
NWS NATIONAL HURRICANE CENTER MIAMI FL AL042014
2100 UTC SAT AUG 23 2014
??? has 40mph winds
Member Since: December 31, 1969 Posts: Comments:

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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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