Karen, TD 13, 97L, new Florida disturbance 98L, and new African disturbance

By: Dr. Jeff Masters , 2:19 PM GMT on September 26, 2007

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Tropical Storm Karen is midway between Africa and the Lesser Antilles Islands. Karen is steadily intensifying, as seen in the latest satellite loops. Low level spirals bands continue to organize, and upper-level outflow is becoming established to the north and south. Wind shear of 10-20 knots is keeping intensification slow,and Karen may not be able to attain hurricane strength this week. Hostile wind shear in association with a trough of low pressure is expected to affect Karen over the next few days, and this trough will also turn the storm to the north or northwest. The models are all fairly unified in taking Karen to a latitude north of the Lesser Antilles Islands. However, the trough of low pressure expected to steer Karen to the northwest is unlikely to be strong enough to recurve Karen out to sea. A new ridge of high pressure may build in, forcing Karen westwards towards the U.S., just north of the Lesser Antilles Islands. This scenario, favored by the UKMET model, would put Karen in a position to threaten the U.S. East Coast late next week. The GFS model does not build in such a strong ridge, and instead forecasts that Karen will stall for 2-4 days a few hundred miles north of the Lesser Antilles Islands, and eventually recurve out to sea when the next strong trough of low pressure comes along. This scenario would put Bermuda at risk from Karen. It is too early to speculate which of these scenarios is more likely, and how much of a risk Karen may present to Bermuda or the U.S. East Coast.


Figure 1. Microwave image from 6:37 am EDT today showing Karen building heavy thunderstorms on the northeast side. Image credit: Navy/NRL.

Tropical Depression 13
Tropical Depression 13 formed yesterday evening in the far southwestern Gulf of Mexico. Satellite imagery and this morning's QuikSCAT pass show a well-organized surface circulation. Most of the winds seen by QuikSCAT were contaminated by rain, so it is difficult to say what the winds are. Wind shear is about 10 knots over the disturbance, and is expected to fall below 5 knots for the next three days. This should allow Tropical Depression 13 to develop into a strong tropical storm--possibly a Category 1 hurricane--before it makes landfall along the Mexican coast 2-3 days from now. Steering currents are weak in the southwest Gulf of Mexico, and the storm will move slowly and erratically. This storm is primarily a threat to Mexico, due to a very strong ridge of high pressure that will prevent the storm from turning northwards. The next Hurricane Hunter flight is scheduled for 2 pm EDT this afternoon.

Tropical wave 97L bringing heavy rain to Puerto Rico
A tropical wave (97L) has brought heavy rains of up to 2-4" to Puerto Rico today. Satellite imagery and Puerto Rico long range radar show heavy but disorganized thunderstorm activity surrounding Puerto Rico and spreading to the Dominican Republic. These heavy rains will spread over northern Haiti Thursday as the wave tracks west-northwest at 10-15 mph. The wave no longer has a closed circulation, and is under 20-30 knots of wind shear. This shear is expected to remain 20-30 knots through Thursday afternoon, preventing any development. When the wave arrives in the eastern Bahamas Thursday night, wind shear is expected to drop to 10 knots, and stay 10-20 knots through Saturday. This may allow some slow development. The UKMET model is forecasting that 97L will become a tropical depression near South Florida on Saturday or Sunday, but none of the other models go along with this prediction.


Figure 2. Radar estimated rainfall from 97L over Puerto Rico.

Disturbed weather over Florida and the Bahamas
An area of disturbed weather has formed over South Florida and the western Bahama Islands, in association with an upper-level trough of low pressure. NHC has labeled this system "98L" this morning. The region is under about 15-20 knots of wind shear, which should keep any development slow today. This disturbance has brought rains of up to four inches to portions of the Florida Keys and the western Bahamas as seen on Miami radar. The thunderstorm activity associated with 98L is currently disorganized, as seen on long range radar out of Miami. The disturbance is expected to lift northeastward in response to a strong trough of low pressure swinging off the U.S. East Coast. On Thursday, when 98L will be over the warm waters of the Gulf Stream approaching North Carolina, the system has the potential to organize into a tropical depression, as wind shear is expected to fall to 10-20 knots. By Friday, the GFS model predicts 98L should be moving rapidly northeastward past Cape Cod, Massachusetts, and could bring heavy rain and high winds to Nantucket, Martha's Vinyard, and eastern Massachusetts. This would not give 98L much time to organize, and at worst 98L should become a weak tropical storm with 45 mph winds. However, the Canadian model predicts that the trough of low pressure pulling 98L northeast will not be strong enough to finish the job, and the storm will stall off the North Carolina coast. I'll have more on this possibility later.

More action off the coast of Africa
An area of disturbed weather has moved off the coast of Africa, and is located a few hundred miles south of the Cape Verdes Islands. This tropical wave is under about 10 knots of wind shear, and has some potential for development over the next few days. Most of the computer models forecast that a tropical depression will form off the coast of Africa in the next 2-5 days.

Wind shear tutorial
For those interested, I've posted a wind shear tutorial. This page is permanently linked on our tropical page.

I'll have an update later today.

Jeff Masters

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1072. BahaHurican
9:41 PM GMT on September 26, 2007
Posted By: Ivansvrivr at 4:48 PM EDT on September 26, 2007.

My guess is still more westerly than models indicate now for karen. Yesterday everybody disagreed.


I didn't disagree yesterday. I think Karen will get a lot closer to PR before shifting, mainly because, as someone said earlier, I don't think the N component of the track will kick in as quickly as forecasted. (Mind u, the forecast looks a lot closer to what I expect than it did yesterday, but then we even forecasted the shift in the models yesterday :o)

I'm hoping this will take a turn similar to 2003's Isabel, but then remain off shore because of whatever the latest trough is. I remember breathing a big sigh of relief when that particular cane turned north, because it was barreling straight for the Bahamas at cat 5, with little fluctuation. . .
Member Since: October 25, 2005 Posts: 19 Comments: 22736
1071. BahaHurican
9:32 PM GMT on September 26, 2007
Posted By: CloudFreak at 4:42 PM EDT on September 26, 2007.

By sharing their knowledge, the US centers SAVE LIVES. THAT'S the point and THAT'S why it's done.


Also it saves American lives in these countries, as well as building good will. Additionally, of all the countries in the ATL zone, the US is the one most able both financially and scientifically at this time to support the costs related to tropical cyclone research and monitoring.
Member Since: October 25, 2005 Posts: 19 Comments: 22736
1069. nrtiwlnvragn
9:21 PM GMT on September 26, 2007
Posted By: sporteguy03 at 9:07 PM GMT on September 26, 2007.

Ok so Karen misses first trough where is this 2nd trough being mentioned? I don't see the NhC say anything about 2nd trough?


NHC doesn't forecast out 240 hours. They have enough issues out at 120 hours.
Member Since: September 23, 2005 Posts: 15 Comments: 11346
1068. BahaHurican
9:20 PM GMT on September 26, 2007
Afternoon everybody,

This is what caught my eye about Karen in the 5 p.m. discussion:

THE 12 FOOT SEAS RADII WERE ADJUSTED OUTWARD BASED UPON OBSERVATIONS
FROM NOAA BUOY 41041.

My thought - Geez, isn't this storm big enough already?

Looks like we won't get a hurricane today, though.

Meanwhile, back at 98L, we had more rain today, some of it torrential. It was already raining when I left home around 6:20 a. m., and except for a brief break between 10:30 and 11:30 continued to do so all day. It's still drizzling outside. This kind of rain pattern is one I associate with June or even August, rather than September, almost October. If the trend continues, it looks likely for continued soggy weather over the Bahamas for the next week.
Member Since: October 25, 2005 Posts: 19 Comments: 22736
1066. chrisrw
9:11 PM GMT on September 26, 2007
Louisiana Boy, those of us here in Bermuda are hoping you are wrong!
1065. Ivansvrivr
9:10 PM GMT on September 26, 2007
444 it takes a while to learn not to take things too personally here. Different people come off different ways and don't always intend to offend others.
1064. TheRepairman
9:08 PM GMT on September 26, 2007
Later everyone!

Got to head home from the office but I'll be back.

Repairman
1063. nash28
9:07 PM GMT on September 26, 2007
Karen is a large system with plenty of moisture in which to pull from....

We have seen countless systems this season that were a microcosm of Karen with nothing but shear and dry air ahead of them survive with the COC in tact, so 15-20kts of shear IMHO is not going to rip her apart.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1062. Caffinehog
9:07 PM GMT on September 26, 2007
louisianaboy444,
If you want an exact science, don't try chemistry, either. Or physics. Or biology.

In any science, meteorology included, we improve the models iteratively as we get more information. Chemistry has been around for over 400 years, and we're still discovering a lot of new things. Ben Franklin first suggested that weather forecasting might be possible about 200 years ago.
Member Since: June 5, 2003 Posts: 0 Comments: 40
1061. louisianaboy444
9:07 PM GMT on September 26, 2007
Posted By: louisianaboy444 at 8:50 PM GMT on September 26, 2007.

i wouldn't blame just the NHC though i mean yes after i woke up and had a Hurricane Humberto at my doorstep i dont trust them anymore.... i just dont take their words in stone anymore....or any meteorologist because as much as we dont want to admit it meteorology needs improvement it's not an exact science yet but we are more accurate now than we've ever been and will probably get even more accurate in the coming years.


i like your style.. :) now can you please tell the global warming alarmists the same thing :)


I certainly leaning towards global warming being a reality but this isnt the place to discuss this if you want to have a convo about that drop me mail :)
Member Since: August 29, 2006 Posts: 22 Comments: 1352
1060. sporteguy03
9:07 PM GMT on September 26, 2007
Ok so Karen misses first trough where is this 2nd trough being mentioned? I don't see the NhC say anything about 2nd trough?
Member Since: July 7, 2005 Posts: 0 Comments: 5417
1059. V26R
9:06 PM GMT on September 26, 2007
Dallas Looks to me like Karen is holding her own!

Link
Member Since: July 20, 2006 Posts: 0 Comments: 1762
1058. StormJunkie
9:06 PM GMT on September 26, 2007
Afternoon all

Dr M has a new blog up

See you there
Member Since: August 17, 2005 Posts: 26 Comments: 16874
1057. Drakoen
9:06 PM GMT on September 26, 2007
New Blog.
Member Since: October 28, 2006 Posts: 57 Comments: 30841
1056. Ivansvrivr
9:05 PM GMT on September 26, 2007
Thats also why those of us along different points of the learning curve should enjoy (and take every oppotunity to) discuss and debate with folks like Drak, Storm etc.




1055. louisianaboy444
9:04 PM GMT on September 26, 2007
I really don't see this being a threat to the U.S. in my opinon if the first trough isnt strong enough to lift it on out the secondary trough will most likely be strong enough...i most certainly think Bermuda could be affected by this though...but thats my educated guess...things could change!
Member Since: August 29, 2006 Posts: 22 Comments: 1352
1053. Drakoen
9:02 PM GMT on September 26, 2007
continues to look very impressive for the time being.
Member Since: October 28, 2006 Posts: 57 Comments: 30841
1051. sporteguy03
9:02 PM GMT on September 26, 2007
Posted By: msphar at 8:59 PM GMT on September 26, 2007.
Shear and track are doing their thing to poor Karen and its not pretty. She may fare worse than Ingrid.

Not so fast...Shear effects larger systems differently then smaller ones like Ingrid.
Member Since: July 7, 2005 Posts: 0 Comments: 5417
1049. Drakoen
9:01 PM GMT on September 26, 2007
The ECMWF is uncertain whether or not it will curve out to sea or head in the general direction of the U.S. east coast.
Member Since: October 28, 2006 Posts: 57 Comments: 30841
1047. bayoubrotha
9:01 PM GMT on September 26, 2007
Shear and track are doing their thing to poor Karen and its not pretty. She may fare worse than Ingrid.

Karen is a much larger storm than Ingrid. Shear will have less impact on her.
Member Since: August 15, 2006 Posts: 0 Comments: 618
1046. louisianaboy444
9:00 PM GMT on September 26, 2007
hey Drak alot of people here are very educated but some people are just here to learn more about it maybe just for information or for a new hobby so yeah i wouldn't pick on people that are maybe not as educated as you because you have to remember how you were when you first started out and the people you learned from....have a good day
Member Since: August 29, 2006 Posts: 22 Comments: 1352
1045. DallasGumby
9:00 PM GMT on September 26, 2007
Posted By: decimus785 at 8:54 PM GMT on September 26, 2007.

kso,karen still has 70 mph winds as i see the latest advisory


However, the NHC says that might be generous. It doesn't look like Karen is intensifying; to the contrary, it appears to be weakening.

FWIW, put me in the fish storm crowd. I just think it's foolish for us to be predicting landfall locations 10 days out. It's a guess on my part, just as it's a guess on those predicting an east coast landfall.
Member Since: August 22, 2007 Posts: 0 Comments: 376
1044. msphar
8:59 PM GMT on September 26, 2007
Shear and track are doing their thing to poor Karen and its not pretty. She may fare worse than Ingrid.
Member Since: August 20, 2006 Posts: 0 Comments: 289
1043. nrtiwlnvragn
8:59 PM GMT on September 26, 2007
Posted By: Floodman at 8:53 PM GMT on September 26, 2007.

Posted By: nrtiwlnvragn at 8:50 PM GMT on September 26, 2007.

Karen Advisory


That's the 11 AM


Sorry about that, link version issue.
Member Since: September 23, 2005 Posts: 15 Comments: 11346
1042. Ivansvrivr
8:58 PM GMT on September 26, 2007
If one mixes guess, a little knowledge, and debate does that make one a half maybe more or less?
1041. nash28
8:58 PM GMT on September 26, 2007
Well, the NHC couldn't ignore the large shift WWD by the models, especially their champion models GFDL and GFS.

Now, let's see if there is any consistency from here on out. The UKMET hasn't budged, and still shows the trough to lift NWD allowing a strong ridge to build back in and steer Karen WWD.

Now, the other models that were recurving are beginning to pick up on this. It is still early, and many things can change. Also, I am not surprised the ECMWF flipped back to a recurve on the 12z. For some reason, that model has had some fits in the Atlantic this year with the flopping back and forth....
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1040. Drakoen
8:58 PM GMT on September 26, 2007
Posted By: FLWeatherFreak91 at 8:54 PM GMT on September 26, 2007.

That's what I realized you were meaning drak


yes then you realize the small amount of educated people LOL.
Member Since: October 28, 2006 Posts: 57 Comments: 30841
1039. gatorman07
8:57 PM GMT on September 26, 2007
With Karren as big as she is, the storm will do what she pleases. If anyone recalls Katrina, the models showed her going to sea or riding the Eastern Seaboard. Due to her size she busted thru a High and the steering current had little effect on her.
1038. Floodman
8:56 PM GMT on September 26, 2007
Posted By: tiggeriffic at 8:50 PM GMT on September 26, 2007.

flood, i will agree with that to a degree. However, if la nina/el nino has caused the season to "lag behind" by a few weeks, the computers are basing the information on what normally happens this time of year from past history, not necessarily with the "lag" in the equation. In this concensus, the models could/would be off, possibly considerably. I also understand that they work also from bouys that only read current conditions, not future, in that they would also be off.


Exactly...though I have to say that I put more faith in the models further into the storm's life cycle, La Nina or not...
Member Since: August 2, 2006 Posts: 10 Comments: 9922
1037. NEwxguy
8:56 PM GMT on September 26, 2007
well based on the 5pm discussion,it looks like Karen has some rough days ahead of it.
Member Since: September 6, 2007 Posts: 888 Comments: 15989
1036. TerraNova
8:56 PM GMT on September 26, 2007
15% chance of disspiation in 72 hours according to the NHC...not a good chance at all and far out in time. IMO I don't think this will dissipate.

nhc
Member Since: July 30, 2007 Posts: 76 Comments: 4063
1035. bayoubrotha
8:55 PM GMT on September 26, 2007
23N, 57W in 120 hours; so that is another left shift in the track from 55.5W at 11a.
Member Since: August 15, 2006 Posts: 0 Comments: 618
1034. nrtiwlnvragn
8:55 PM GMT on September 26, 2007
Recon about half way there, last reported position 12.9N 52.9W
Member Since: September 23, 2005 Posts: 15 Comments: 11346
1033. Hurricane1956
8:55 PM GMT on September 26, 2007
Hello everybody,any chance of 98L becoming a TD before crossing over florida to the east atlantic? your thoughs.
Also I notice like 97L is relocated to south of Puerto Rico,any chance for this to redevelop,Dr.Masters mention it might develop later on on the week as it approach South Florida.Any comments will be greatly appreciatted.
Member Since: August 28, 2006 Posts: 0 Comments: 638
1032. CloudFreak
8:55 PM GMT on September 26, 2007
I heard from some Karen-is-a-fish people... they all got together to try to figure out how to make crow-sticks.
1031. FLWeatherFreak91
8:54 PM GMT on September 26, 2007
That's what I realized you were meaning drak
Member Since: December 1, 2006 Posts: 2 Comments: 3634
1030. Drakoen
8:54 PM GMT on September 26, 2007

WTNT42 KNHC 262049
TCDAT2
TROPICAL STORM KAREN DISCUSSION NUMBER 8
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL122007
500 PM EDT WED SEP 26 2007

KAREN'S INTENSIFICATION...AT LEAST FOR THE TIME BEING...HAS
HALTED. THE INTERMITTENT EYE IS NO LONGER PRESENT AND DEEP
CONVECTION IS MAINLY OCCURRING IN THE NORTHEASTERN SEMICIRCLE.
SUBJECTIVE DVORAK ESTIMATES REMAIN AT 4.0 AND 3.5 FROM TAFB AND
SAB...THOUGH THE ADVANCED DVORAK TECHNIQUE CONTINUES TO SUGGEST AN
INTENSITY A BIT LOWER AT 50-55 KT. AN 1835Z AMSU CIMSS ESTIMATE
ALSO GIVES A WIND OF 57 KT FOR KAREN. INITIAL INTENSITY IS KEPT AT
60 KT... THOUGH THIS MAY BE SOMEWHAT GENEROUS.

KAREN IS MOVING AT 295/10 UNDER THE INFLUENCE OF A LOW- TO MID-LEVEL
RIDGE TO ITS NORTH. A TROUGH IN THE UPPER TROPOSPHERE LOCATED WEST
OF KAREN IS PREDICTED TO RETROGRADE WESTWARD AND INDUCE ENOUGH OF A
WEAKNESS IN THE RIDGE TO TURN KAREN TOWARD THE NORTHWEST BETWEEN
DAYS 3 AND 5. THE MODEL CONSENSUS HAS SHIFTED SLIGHTLY TO THE WEST
IN THE 12Z RUNS. THE TRACK FORECAST IS CONSISTENT WITH THAT
GUIDANCE EXCEPT TO PUT LESS WEIGHT ON THE GFS EARLY ON...DUE TO ITS
TOO RAPID INITIAL MOTION...AND THE NOGAPS AT DAYS 4 AND 5...DUE TO
ITS UNREALISTICALLY LARGE VORTEX AND NORTHWARD MOTION.

AS IN MANY CASES...THE INTENSITY FORECAST IS NOT CLEAR CUT. KAREN
REMAINS OVER WARM 28C WATER AND HAS ABUNDANT MOISTURE NEARBY BUT IS
BEING IMPACTED BY MODERATE 15-20 KT WESTERLY SHEAR. THE SHEAR
SHOULD CONTINUE AND PERHAPS BE ENHANCED DURING THE NEXT THREE DAYS.
THE SHIPS AND LGM STATISTICAL GUIDANCE SUGGEST MODEST
INTENSIFICATION DURING THE NEXT DAY...BUT THIS MAY BE OVERLY
INFLUENCED BY THEIR PERSISTENCE PREDICTOR. THE GFDL AND HWRF
DYNAMICAL GUIDANCE ARE LESS IMPRESSED WITH THE POTENTIAL FOR
INTENSIFICATION. THE OFFICIAL INTENSITY FORECAST BRINGS KAREN TO A
HURRICANE...BUT JUST BARELY...IN A DAY BEFORE A GRADUAL WEAKENING
THEREAFTER. HOWEVER...IF THE SHEAR CONTINUES TO ADVERSELY IMPACT
KAREN'S ABILITY TO MAINTAIN SYMMETRIC CONVECTION...THEN THE CYCLONE
MAY BE SIGNIFICANTLY WEAKER THAN PREDICTED HERE.
Member Since: October 28, 2006 Posts: 57 Comments: 30841
1029. TerraNova
8:54 PM GMT on September 26, 2007
what direction is Karen moving?
still wnw or nw


WNW near 12 miles per hour.
Member Since: July 30, 2007 Posts: 76 Comments: 4063
1028. decimus785
8:54 PM GMT on September 26, 2007
kso,karen still has 70 mph winds as i see the latest advisory
1027. Drakoen
8:54 PM GMT on September 26, 2007
yes it is alot of halves. You start out with a whole and then you keep dividing by a half.
Member Since: October 28, 2006 Posts: 57 Comments: 30841
1026. Floodman
8:53 PM GMT on September 26, 2007
Posted By: nrtiwlnvragn at 8:50 PM GMT on September 26, 2007.

Karen Advisory


That's the 11 AM
Member Since: August 2, 2006 Posts: 10 Comments: 9922
1025. TerraNova
8:53 PM GMT on September 26, 2007
The forecast track has shifted and now takes Karin a bit farther south...

nhc
Member Since: July 30, 2007 Posts: 76 Comments: 4063
1024. decimus785
8:53 PM GMT on September 26, 2007
what direction is Karen moving?
still wnw or nw
1023. extreme236
8:53 PM GMT on September 26, 2007
BBL
Member Since: August 2, 2007 Posts: 19 Comments: 19234
1022. CloudFreak
8:53 PM GMT on September 26, 2007
Posted By: Ivansvrivr at 8:51 PM GMT on September 26, 2007.

For some reason you notice more when folks disagree w/you. The Karen is a fish storm crowd must be sticking to lurking today.

LOL!

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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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