ATL : TROPICAL DEPRESSION ERIKA (06L)

[HURAKAN]

Best Track 12z:

AL, 06, 2009090212, , BEST, 0, 163N, 600W, 40, 1008, TS

[jconsor]

I agree with Air Force Met about the swirl near Guadeloupe being a smaller vortex rotating around a larger center. The recon found an 1008 mb pressure near 16.5N 59.5W at 1130z, 3 mb lower than the pressure at Guadeloupe at 12z. That suggests the main center is still about 100 miles east of Guadeloupe.

The satellite image in this surface plot is a little old, but you can clearly see the LLC near northern Guadeloupe Island. Obs all around fit THAT as being the real center of Erika. I don't see any evidence on satellite or surface obs of a large gyre with multiple vortices now.

Have I mentioned that I hate storms like this lately?

[Air Force Met]

however, recon is flying at 850mb. Wonder if that vtx is not quite reaching the surface

As I said...I'm seeing low level clouds headed into that blob...those are below 850.

Its possible...but how many times have we seen a TC with a broad circulation spit out a vort center only to spin up another one under the convection? I think that is what's happening now.

WHY its happening? can't explain. SAL...undercutting shear...who knows. All I know is it has great upper level outflow and deep deep convection. Should be going ape.

[xironman]

That little vort max shows up nicely if you animate the radar http://www.meteo.fr/temps/domtom/antilles/pack-public/animation/animMOSAIC2.html

[Weatherboy1]

I just want to say (off topic) that it's great to have multiple professionals on here sharing their observations. It's helpful for us amateurs. I'll second what wxman57 said earlier, these formative/disorganized systems stink. Can't we just get a nice, easy to track, easy to model, vertically stacked system for a change? Sure would save a lot of hair-pulling-out by all of us storm nuts. LOL

[wxman57]

however, recon is flying at 850mb. Wonder if that vtx is not quite reaching the surface

Yeah, was thinking that. The plane is measuring the wind field 5000 ft up. Note the new 12Z NHC position is 16.3N/60W. Don't see anything there, it may be a compromise position. I just don't see any surface obs to support a center to the east near the convection.

[Blown Away]

Bams way west now, the recurve theory is going to be very close to SFL at this point.

[storms NC]

Looking at these maps, I would say Erika is FAR from being very disorganized. Great Low Level Convergence, along with good Upper divergence and little shear will get this think cranking today. I think it went through some center reformations overnight which explains the SW motion.

http://cimss.ssec.wisc.edu/tropic/real- ... 8conv.html

http://cimss.ssec.wisc.edu/tropic/real- ... g8dvg.html

http://cimss.ssec.wisc.edu/tropic/real- ... g8shr.html

They said she has more than one center.

WTNT41 KNHC 020859
TCDAT1
TROPICAL STORM ERIKA DISCUSSION NUMBER 3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL062009
500 AM AST WED SEP 02 2009

AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT HAS BEEN SEARCHING
FOR THE CENTER OF THE TROPICAL STORM OVER THE PAST FEW HOURS. THE
CIRCULATION HAS BECOME QUITE DISORGANIZED...BUT IT APPEARS THAT THE
CENTER HAS REFORMED TO THE SOUTHWEST OF THE PREVIOUSLY ESTIMATED
TRACK. HOWEVER THE FLIGHT-LEVEL WINDS SUGGEST THAT THERE MAY BE
MULTIPLE CENTERS...SO THE ADVISORY POSITION IS HIGHLY UNCERTAIN AND
PROBABLY REPRESENTS A MEAN CENTER...OR THE LOCATION OF THE
LOW-LEVEL VORTICITY MAXIMUM. THE INITIAL MOTION...270/4...IS OF
COURSE ALSO HIGHLY UNCERTAIN. TO MAINTAIN SOME CONTINUITY FROM THE
PREVIOUS FORECAST AND FOLLOWING THE TRACK GUIDANCE...A WEST-
NORTHWESTWARD TRACK IS PREDICTED TO RESUME. ERIKA SHOULD BE
STEERED BY THE FLOW TO THE SOUTH OF A WEAK SUBTROPICAL RIDGE FOR A
COUPLE OF DAYS. LATER IN THE FORECAST PERIOD...DYNAMICAL GUIDANCE
SHOWS A MORE NORTHWESTWARD MOTION FOR A STRONGER CYCLONE...E.G. THE
GFDL AND HWRF...AND A CONTINUED WEST-NORTHWESTWARD MOTION FOR A
WEAKER SYSTEM...E.G. THE GFS. THIS IS A LOW-CONFIDENCE TRACK
FORECAST.

DATA FROM THE AIRCRAFT INDICATE THAT ERIKA HAS WEAKENED A LITTLE...
WHICH IS NOT SURPRISING CONSIDERING THE DISORGANIZED APPEARANCE OF
THE SYSTEM ON SATELLITE IMAGES. MODERATE WESTERLY SHEAR HAS BEEN
DISRUPTING THE CYCLONE BUT THE SHEAR IS NOT EXPECTED TO BE STRONG
ENOUGH TO PREVENT SOME STRENGTHENING DURING THE NEXT DAY OR SO.
THEREAFTER...AN UPPER-TROPOSPHERIC TROUGH FARTHER TO THE WEST IS
LIKELY TO IMPART INCREASING SOUTHWESTERLY SHEAR ON ERIKA...WHICH
SHOULD INDUCE WEAKENING. THE NHC INTENSITY FORECAST IS VERY
SIMILAR TO THE PREVIOUS OFFICIAL FORECASTS...BUT BELOW THE
CONSENSUS OF THE NUMERICAL INTENSITY GUIDANCE. IT SHOULD BE NOTED
THAT SOME OF THESE NUMERICAL MODELS...SUCH AS THE HWRF AND GFDL...
HAVE SHOWN A HIGH BIAS FOR A COUPLE OF THIS YEAR'S ATLANTIC
TROPICAL CYCLONES.

GIVEN THE SOUTHWARD SHIFT IN THE TRACK...A TROPICAL STORM WARNING
HAS BEEN ISSUED FOR THE NORTHERN LEEWARD ISLANDS.

FORECAST POSITIONS AND MAX WINDS

INITIAL 02/0900Z 17.0N 59.0W 45 KT
12HR VT 02/1800Z 17.3N 60.1W 50 KT
24HR VT 03/0600Z 17.8N 61.5W 55 KT
36HR VT 03/1800Z 18.4N 62.9W 55 KT
48HR VT 04/0600Z 19.0N 64.3W 55 KT
72HR VT 05/0600Z 20.3N 66.9W 50 KT
96HR VT 06/0600Z 22.0N 69.5W 45 KT
120HR VT 07/0600Z 24.0N 72.0W 45 KT

[Evil Jeremy]

06z/12z summary of the SFWMD models:

The 12z BAM models continue to be the southern outliers, taking Erika across PR and Hispaniola and into Cuba. The 06z GFDL has moved south and west joining the 00z UKMET and the new 06z GFS with takes Erika into SE FL. The HWRF is the NE outlier, moving about WNW to NW the entire run, bending to the west at the end. The 06z NOGAPS is the only model that shows a recurve, and has Erika not hit any land areas directly. The overall consensus is now more west and south, and below the NHC forecast points.

These models don't seem to take into account Erika's SW motion this morning.

[wxman57]

however, recon is flying at 850mb. Wonder if that vtx is not quite reaching the surface

As I said...I'm seeing low level clouds headed into that blob...those are below 850.

Its possible...but how many times have we seen a TC with a broad circulation spit out a vort center only to spin up another one under the convection? I think that is what's happening now.

WHY its happening? can't explain. SAL...undercutting shear...who knows. All I know is it has great upper level outflow and deep deep convection. Should be going ape.

Yeah, you're right, we've seen weak multi-vortex systems many times. A vortex moving away from the convection can't sustain itself. Either it dies and another forms near the convection or the TS dies. But note the SE wind at 20 kts on my plot above that seems to point perpendicular to the low cloud flow into the convection. Could be a bad wind direction from that ship. I don't trust ships much.

[Evil Jeremy]

could be a SAL surge. One was catching up yesterday.

Does not look like there is SAL near Erika: http://cimss.ssec.wisc.edu/tropic/real- ... split.html

[AdamFirst]

Throwing this out there, I didn't know Weather Underground is now posting Quikscat photos



This is dated, though. I think.

[wxman57]

One major clue that the center near Guadeloupe isn't the actual real center is that it is now moving to the south. Good indication that it's rotating around another center farther east. Possibly near 16.5/59.5.

[Evil Jeremy]

promets, what do you think Erika's path could be like now? Where do you see Erika in 5 days?

[BobHarlem]

That little vort max shows up nicely if you animate the radar http://www.meteo.fr/temps/domtom/antilles/pack-public/animation/animMOSAIC2.html

Even easier to see it here http://flhurricane.com/imageanimator.php?69 (Longer term radar loop)

[Air Force Met]

Yeah, you're right, we've seen weak multi-vortex systems many times. A vortex moving away from the convection can't sustain itself. Either it dies and another forms near the convection or the TS dies. But note the SE wind at 20 kts on my plot above that seems to point perpendicular to the low cloud flow into the convection. Could be a bad wind direction from that ship. I don't trust ships much.

I do know this...this is a pain in the rear. Why can't they be easy? Makes our job that much more impossible (if that's possible).

If that does decide to become the center...complete with some convection...that'll throw the track off some lol.

[sevenleft]

One major clue that the center near Guadeloupe isn't the actual real center is that it is now moving to the south. Good indication that it's rotating around another center farther east. Possibly near 16.5/59.5.

This is where the most recent recon fix was.

[Stormcenter]

It doesn't matter where she goes (west,wnw or nw)conditions may not be favorable for any significant development the more she moves westward.

You never know, but there my not be much left of Erika for models to track in another 24hrs, She looks very disorganized.

[storms NC]

One major clue that the center near Guadeloupe isn't the actual real center is that it is now moving to the south. Good indication that it's rotating around another center farther east. Possibly near 16.5/59.5.

That is where the NHC put her at at 8:00 AM.
From NHC
[8:00 AM AST Wed Sep 2
Location: 16.5°N 59.5°W
Max sustained: 45 mph
Moving: W at 7 mph
Min pressure: 1008 mb]

[wxman57]

promets, what do you think Erika's path could be like now? Where do you see Erika in 5 days?

I'll let you know when I figure out where it'll be for the next advisory at 10am CDT. Maybe the GFS will turn out to be correct. Very weak system moving into south FL?