Karen Having Trouble With Dry Air and High Wind Shear

By: Dr. Jeff Masters , 8:25 PM GMT on October 03, 2013

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Tropical Storm Karen is having trouble with dry air and high wind shear as the storm heads north-northwest at 12 mph into the Gulf of Mexico. An Air Force hurricane hunter plane is in the storm, and found top surface winds near 65 mph between 3:30 - 4:30 pm EDT Thursday, and a central pressure of 999 mb, 5 mb lower than this morning's. Satellite loops show that Karen is a medium-sized storm whose heavy thunderstorms have declined in intensity and areal coverage since this morning. The heavy thunderstorms are all on the northern and eastern flanks of the storm, and the low-level center is exposed to view. High wind shear of 20 knots, due to strong upper-level winds out of the west-southwest, is driving dry air from the Western Gulf of Mexico into Karen's core. Heavy thunderstorms are having difficulty building on the west and south sides of Karen's center of circulation because of the shear, resulting in a lopsided comma-shape on satellite imagery. Karen is attempting to build an eyewall, and has managed to wrap a band of heavy thunderstorm about half way around its center. If this band wraps all the way around, Karen will likely be able to intensify into a Category 1 hurricane. Karen has a strong upper-level outflow channel to its north that is helping ventilate the storm, and ocean temperatures are a very warm 29°C (84°F). Ocean heat content is about 30 kJ per square centimeter, which is fairly typical for this time of year, and does not increase the odds of rapid intensification. Strong southeasterly winds ahead of Karen are already pushing tides 1 - 1.5' above normal along the coast from Eastern Louisiana to Alabama, as seen on our wundermap with the storm surge layer turned on.


Figure 1. Predicted 3-day rainfall totals for Karen, generated at 3:14 pm EDT Thursday October 3, 2013. NHC now puts this product on their website.


Figure 2. Ocean heat content (also called the Tropical Cyclone Heat Potential, TCHP) for October 3, 2013, along the path of Tropical Storm Karen, was about 20 - 40 kJ per square centimeter. This is a fairly ocean heat content for this time of year, and does not increase the odds of rapid intensification. TCHP values above about 75 kJ per square centimeter are typically associated with rapid intensification. Image credit: NOAA/RAMMB.

Forecast for Karen
Wind shear is expected to increase as the storm heads north-northwest, and shear will be quite high, 25 knots, on Saturday, as Karen closes in on the U.S. Gulf Coast, according to the 2 pm EDT SHIPS model forecast. The atmosphere will grow drier as Karen moves into the Northern Gulf of Mexico, and the drier air combined with increasing wind shear will retard development, making only slow intensification likely through Friday. A trough of low pressure and an associated cold front will be moving through Louisiana on Saturday, and the associated upper-level westerly winds will be able to turn Karen more to the northeast as it approaches the coast on Saturday. The higher shear, combined with ocean temperatures that will drop to 28°C, should be able to induce weakening, and the 5 pm EDT Thursday wind probability forecast from NHC gave a 23% chance Karen will be a hurricane at 2 pm EDT Saturday, down from 41% odds at 2 am EDT Saturday.

The models are split into two camps for Karen's track. The European, UKMET, and GFDL models have Karen making landfall over Central or Eastern Louisiana. These models keep Karen relatively weak, resulting in a path that follows the low-level winds more to the west, where there is more dry air and higher wind shear. The GFS model and HWRF model keep Karen stronger, and predict a landfall in the Western Florida Panhandle. NHC is splitting the difference between these two solutions, which is a reasonable compromise. Most of Karen's heavy thunderstorms will be displaced to the east by high wind shear when the storm makes landfall, and there will likely be relatively low rainfall totals of 1 - 3" to the immediate west of where the center. Much higher rainfall totals of 4 - 8" can be expected to the east. To judge the possibilities of receiving tropical storm-force winds at your location, I recommend using the NHC wind probability forecast. The highest odds of tropical storm-force winds (44 - 66%), according to NHC's 5 pm EDT Thursday forecast, are along the coast from Buras, Louisiana, to Pensacola, Florida.


Figure 3. A possible analogue for Karen: Hurricane Ida of 2009 followed a path very similar to Karen's, and was a hurricane just south of Louisiana before suddenly weakening to an extratropical storm with 40 - 50 mph winds as it made landfall in Alabama.

A possible analogue for Karen: Hurricane Ida of 2009
We have little skill forecasting intensity, and I expect that at landfall, Karen has a 20% probability of being a Category 1 hurricane with 75 - 85 mph winds, and a 20% chance of being a minimal tropical storm with 40 - 45 mph winds. One possible scenario is a repeat of what happened with Hurricane Ida of 2009. Ida took a track very similar to Karen's, and was a hurricane with 75 mph winds just south of the mouth of the Mississippi River in Louisiana. High wind shear from an approaching trough of low pressure, combined with cooler ocean temperatures near shore, combined to cause a sudden weakening of the storm. Ida became extratropical a few hours before making landfall on the Alabama coast, and brought top sustained winds of 40 - 50 mph to the coast from Shell Beach, Louisiana to Waveland, Mississippi.

Jeff Masters

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1742. seer2012
4:03 PM GMT on October 04, 2013
Quoting 1565. Patrap:
Ahh, we have plenty of wunderground secret decoder rings for Winning your forecast.

Congratulations!!

Do you deliver or does one have to personaly pick it up?
Member Since: July 30, 2012 Posts: 4 Comments: 614
1741. nola70119
2:45 PM GMT on October 04, 2013
Its really going to come down to the interaction with that cold front and that is hard to predict....
Member Since: June 16, 2006 Posts: 0 Comments: 1560
1740. nola70119
2:43 PM GMT on October 04, 2013
I thought she was sheared to death last night BUT In the Gulf you never know.....loops starting to look a little less de-coupled now.
Member Since: June 16, 2006 Posts: 0 Comments: 1560
1739. FutureWx6221
2:35 PM GMT on October 04, 2013
An interesting scenario for Floridacasters to ponder is the one shown by BAMS. Notice how it actually has Karen moving farther west than any other model? This allows more time over water, waiting for the front to come and pick it up. This is reflected in the sharp W to WSW movement predicted by BAMS and some of the GFS ensembles. The timing works out such that if the storm stays further east, it will be more northerly by the time the front comes, sweeping Karen across the CONUS. The more west the system tracks, the farther south it will be when it begins to interact with the front. This could cause a landfall along the west coast of Florida (very unlikely, as shear would have to let up a good deal for the storm to strengthen enough to be pulled west).
Member Since: June 26, 2012 Posts: 0 Comments: 188
1738. weathermanwannabe
2:35 PM GMT on October 04, 2013
The sun is rising and the visible loops are showing some building convection again near/over the coc where there was a naked swirl a few hours ago.

Like a roller coaster ride for the last 6 hours; it's going to boil down to relative sheer levels over the next two days as this system is very persistent.
Member Since: August 8, 2006 Posts: 0 Comments: 8311
1737. longislander102
2:26 PM GMT on October 04, 2013
What would worse case scenerio be for New Orleans with storm surge if Karen goes just to the west before making that turn for the east?
Member Since: August 27, 2011 Posts: 0 Comments: 137
1736. IKE
2:13 PM GMT on October 04, 2013
Convection continuing to fire near/over the COC.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
1735. guygee
2:09 PM GMT on October 04, 2013
Quoting 1657. SheetUnion222Man:
...aluminum and barium aeresol spraying...
If people would just stop recycling their aluminum cans and barium enemas we could foil these nefarious plots.

What is an "aeresol" anyways?
Member Since: September 16, 2005 Posts: 0 Comments: 3060
1734. weatherbro
2:05 PM GMT on October 04, 2013
Quoting 1623. LargoFl:
now THIS is what I myself am watching out for..this being October..Notice the HUGE change in the Bams model track....


Member Since: May 26, 2007 Posts: 47 Comments: 1214
1733. GatorWX
1:50 PM GMT on October 04, 2013
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1732. pottery
1:47 PM GMT on October 04, 2013
Quoting mopapa:
Okay, I have a really stupid question. I'm sure it's been asked and answered and y'all are tired of it, but... How do you know what the "center" of a storm is? To me the "center" would be the middle. Obviously not, though. Any info appreciated. Thanks.

The ''center'' refers to the center of the Circulation (if there is one, and in this case there is).
The satelite images show the storm, and the true center of circulation is just to the right and partially under the cloud.

You can see it well, in post 1718.
Member Since: October 24, 2005 Posts: 0 Comments: 23115
1731. Patrap
1:45 PM GMT on October 04, 2013
Member Since: July 3, 2005 Posts: 415 Comments: 125753
1730. icmoore
1:45 PM GMT on October 04, 2013
Quoting 1717. Sfloridacat5:
Be interesting to see the 12z GFS. If the GFS continues to show a hard right turn we could see an adjustment in the NHC official forecast.

But I'm not sold on the GFS forecast. But saying that, I trust the GFS over any other model.


I gained a lot of trust in the GFS with Debby.
Member Since: July 18, 2005 Posts: 9 Comments: 4141
1729. LargoFl
1:45 PM GMT on October 04, 2013
Quoting 1727. LargoFl:
wherever it does go..its rains are going to add to the fronts rains..rainy few day coming for the east coast states next week.
Member Since: August 6, 2011 Posts: 4 Comments: 33491
1728. WunderAlertBot (Admin)
1:44 PM GMT on October 04, 2013
JeffMasters has created a new entry.
1727. LargoFl
1:44 PM GMT on October 04, 2013
Quoting 1720. hurricanes2018:
its the storm path keep going east maybe it will move up the east coast and go back in the warm water and be a big tropical storm or a big northeaster for the northeast!!!
whever it does go..its rains are going to add to the fronts rains..rainy few day coming for the east coast states next week.
Member Since: August 6, 2011 Posts: 4 Comments: 33491
1726. barbamz
1:44 PM GMT on October 04, 2013

May I repost this screenshot of the last recon visit into Karen from earlier? Might have been a little wobble to the Northeast at the last pass, but you never know. Next recon flight will tell us for sure.
Member Since: October 25, 2008 Posts: 45 Comments: 5039
1725. Unconquered
1:43 PM GMT on October 04, 2013
Quoting 1716. MississippiWx:


Center is still on the western edge of the convection west of 90W.



Shadow playing eye tricks on me I guess.
Member Since: October 3, 2013 Posts: 0 Comments: 5
1724. mopapa
1:43 PM GMT on October 04, 2013
Okay, I have a really stupid question. I'm sure it's been asked and answered and y'all are tired of it, but... How do you know what the "center" of a storm is? To me the "center" would be the middle. Obviously not, though. Any info appreciated. Thanks.
Member Since: August 17, 2011 Posts: 0 Comments: 3
1723. Camille33
1:43 PM GMT on October 04, 2013
Quoting 1721. DellOperator:
Looks like Karen might be losing some westerly component and steering a more northerly heading now as convention begins to develop around the COC.


Lets hope you right
Member Since: July 2, 2013 Posts: 0 Comments: 1256
1722. 7544
1:43 PM GMT on October 04, 2013
Quoting 1694. LargoFl:
watching it closely for that to happen..october that happens alot.


morning i see that bam model still not givin in and now tries to turn her further south and som gfs essembles show it too . she did the split tho and convection heading east maybe thats what the bam was showing and could that convection head east over the sw fl to se fl or will it fizzle out
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1721. DellOperator
1:40 PM GMT on October 04, 2013
Looks like Karen might be losing some westerly component and steering a more northerly heading now as convention begins to develop around the COC.
Member Since: May 31, 2007 Posts: 0 Comments: 185
1720. hurricanes2018
1:40 PM GMT on October 04, 2013
its the storm path keep going east maybe it will move up the east coast and go back in the warm water and be a big tropical storm or a big northeaster for the northeast!!!
Member Since: March 12, 2013 Posts: 7 Comments: 11121
1719. StormPro
1:40 PM GMT on October 04, 2013
OK people, lower Plaquemines parish, the mouth of the Mississippi river(toe of the boot) is NOT New Orleans. Please look at a map before you post that "NOLA is getting hit in every model!!!!"
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1718. ProgressivePulse
1:40 PM GMT on October 04, 2013
Good shot of Karen

Member Since: August 19, 2005 Posts: 5 Comments: 4863
1717. Sfloridacat5
1:39 PM GMT on October 04, 2013
Be interesting to see the 12z GFS. If the GFS continues to show a hard right turn we could see an adjustment in the NHC official forecast.

But I'm not sold on the GFS forecast. But saying that, I trust the GFS over any other model.
Member Since: September 16, 2007 Posts: 0 Comments: 4809
1716. MississippiWx
1:39 PM GMT on October 04, 2013
Quoting 1702. Unconquered:
Last few visible satellite images indicate that the COC has jogged to the east. COC now east of 90W. It was directly over 90W in her birthday suit but convection has now covered her.


Center is still on the western edge of the convection west of 90W.

Member Since: July 15, 2006 Posts: 17 Comments: 10157
1715. Unconquered
1:38 PM GMT on October 04, 2013
Quoting 1705. Patrap:
She sure gained a lot of latitude overnight.


She was moving close to 20MPH overnight but slowing of forward speed is anticipated. The water vapor imagery of Eastern United States illustrates to issue Karen will have moving Northward. The High pressure system centered over the Carolina's is digging all the way down to Florida Georgia border. She can't go North much longer the door is slamming shut to the west as the cold front approaches. Only one place to go.
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1714. Patrap
1:37 PM GMT on October 04, 2013
Larger image

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1713. LargoFl
1:37 PM GMT on October 04, 2013
well IF the GFS verifies..some Heavy sustained winds for My area as well and this is KTS not MPH
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1712. hurricanehanna
1:37 PM GMT on October 04, 2013
Quoting 1710. LargoFl:
ok thanks.

I think it's just a lot of dry air out ahead of the front....
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1711. RyanSperrey
1:36 PM GMT on October 04, 2013
Remember when the season started and we were all making storm track comparisons to 2005 and saying how amazingly active this season was going to be?

lol.
Member Since: October 25, 2012 Posts: 0 Comments: 175
1710. LargoFl
1:36 PM GMT on October 04, 2013
Quoting 1706. hurricanehanna:


I may be wrong Largo, but the front isn't supposed to make it's way through our area (S. La) until Late Saturday....
ok thanks.
Member Since: August 6, 2011 Posts: 4 Comments: 33491
1709. Patrap
1:35 PM GMT on October 04, 2013

Sunrise and a peek under Karen's hood from NEXSAT/GOM Loop
Member Since: July 3, 2005 Posts: 415 Comments: 125753
1708. Times2
1:35 PM GMT on October 04, 2013
Link

color enhancement pretty much says it all....sucking dry air...that will take the wind out of her and uh oh the front cometh
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1707. Xyrus2000
1:34 PM GMT on October 04, 2013
Quoting 1698. southernema:



Pascagoula is in MS


Oops. I should know better than to post without my coffee. :P
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1706. hurricanehanna
1:34 PM GMT on October 04, 2013
Quoting 1700. LargoFl:
that dry air..IS that the front coming in?


I may be wrong Largo, but the front isn't supposed to make it's way through our area (S. La) until Late Saturday....
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1705. Patrap
1:34 PM GMT on October 04, 2013
She sure gained a lot of latitude overnight.
Member Since: July 3, 2005 Posts: 415 Comments: 125753
1704. Xyrus2000
1:33 PM GMT on October 04, 2013
Quoting 1688. Unconquered:


The GFS last run is very interesting. Instead of Karen curving to to the right, she now hooks to the right.


Well, I posted my opinion so the storm will do the complete opposite. :D
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1703. Patrap
1:32 PM GMT on October 04, 2013
Storm Relative 1 km Geostationary Visible Imagery

Member Since: July 3, 2005 Posts: 415 Comments: 125753
1702. Unconquered
1:32 PM GMT on October 04, 2013
Last few visible satellite images indicate that the COC has jogged to the east. COC now east of 90W. It was directly over 90W in her birthday suit but convection has now covered her.
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1701. hurricanes2018
1:32 PM GMT on October 04, 2013
MAYBE A SUPER STORM MOVING UP THE EAST COAST
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1700. LargoFl
1:31 PM GMT on October 04, 2013
Quoting 1691. MahFL:
Some very dry air on the west side though.

that dry air..IS that the front coming in?
Member Since: August 6, 2011 Posts: 4 Comments: 33491
1699. gordydunnot
1:31 PM GMT on October 04, 2013
One thing about all those models they seem to have it visiting New Orleans before going somewhere else.
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1698. southernema
1:31 PM GMT on October 04, 2013
Quoting 1690. Xyrus2000:
My opinion now is that Karen will most like be a moderate TS at landfall, which will occur somewhere between the south-eastern NOLA peninsula and Pascagoula, AL. My gut feel says it will be pretty close to NOLA though.

Looking at the shear forecast, it appears there will only be a small window where shear will let up about 36 hours from now before shear kicks up again along the coast. Along with this, the steering currents have the storm heading on pretty much a northern route.

Given the dry air and Karen's current conditions, it just doesn't seem that there will be much of a chance to intensify over the next couple of days before landfall.



Pascagoula is in MS
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1697. LargoFl
1:30 PM GMT on October 04, 2013
Gem brings it into LA then northward..i dont think the front will allow that to happen....
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1696. MahFL
1:30 PM GMT on October 04, 2013
A big hook to the right would surprise a few people.
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1695. drs2008
1:29 PM GMT on October 04, 2013
Quoting 1683. CaneHunter031472:


I noticed, nd I hope it doesn't decide to intensify in the last minute.
a la Opal!
Member Since: July 4, 2008 Posts: 1 Comments: 176
1694. LargoFl
1:29 PM GMT on October 04, 2013
Quoting 1688. Unconquered:


The GFS last run is very interesting. Instead of Karen curving to to the right, she now hooks to the right.
watching it closely for that to happen..october that happens alot.
Member Since: August 6, 2011 Posts: 4 Comments: 33491
1693. CaneHunter031472
1:29 PM GMT on October 04, 2013
Quoting 1671. MahFL:
Looks like the shear let up a touch.

Yes the worse shear is now to Karens east.


I wonder if the shear forecast will pan out, or f it will be weaker than expected.
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1692. Patrap
1:28 PM GMT on October 04, 2013
New Orleans
NEXRAD Radar

Velocity Azimuth Display Wind Profile ° Elevation
Range 124 NMI

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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.