Atlantic Tropical Action 2012 - Part I

[wxmx]

Anybody else see shades of 2007 with this invest? It reminds me of those '07 storms that sailed straight lines through the Caribbean.

Yeah, now that you mention it, it sorta looks like Olga.

[Ed Lizard]

Anybody else see shades of 2007 with this invest? It reminds me of those '07 storms that sailed straight lines through the Caribbean.

That was a different ENSO than we have now.

[Ed Lizard]

Yeah, now that you mention it, it sorta looks like Olga.

I had to Wiki that one...

[icebreaker5221]

There's already an upper level ridge near atop of the low, so it could transition rather fast...so if it becomes a named system I'd favor a tropical over a subtropical one...it just needs to detach from the front...being over the Gulf stream doesn't hurt either

I agree. I think the system off the SC coast has a better chance of becoming a named system over the next 48 hrs than invest 99L. Warm SSTs, good convective coverage and nice enhancement of UL divergence courtesy right-entrance positioning relative to that jet-streak to the NE of it.

Hopefully NHC will give it a probability at the next update. Personally, I would go with 50%.

[wxmx]

I agree. I think the system off the SC coast has a better chance of becoming a named system over the next 48 hrs than invest 99L. Warm SSTs, good convective coverage and nice enhancement of UL divergence courtesy right-entrance positioning relative to that jet-streak to the NE of it.

Hopefully NHC will give it a probability at the next update. Personally, I would go with 50%.

Just in time to break the 0 in the bottom of the 9th, much to Ed's chagrin.

[Ed Lizard]

Just in time to break the 0 in the bottom of the 9th, much to Ed's chagrin.

Isn't vertically aligned well yet, pressures aren't super low, and lowest pressure still onshore.

But I am nervous.

[Ed Lizard]

Through 96 hours, Euro finally seeing 99L, looks to be on similar path to GFS.

[Srain]

[wxmx]

Through 96 hours, Euro finally seeing 99L, looks to be on similar path to GFS.

No weakness in between the Bermuda and central plains ridge = straight Wward trajectory.

[Superstorm93]

That EC Blob has become a bit more interesting. Doubt we'll see the NHC jump on this until it really shows some organization.

EDIT: Of course the HRRR is blowing this up into some 60kt + system off of NC.

SPC on the blob.

"REGIONAL RADAR IMAGERY OVER NERN SC INDICATED AN AREA OF BROAD LOW

LEVEL CIRCULATION CENTERED OVER HORRY COUNTY SC...WITH THIS

CIRCULATION A SUB-SYNOPTIC LOW LOCATED ALONG A WIND SHIFT EXTENDING

NEWD FROM THE PRIMARY LOW OVER SERN GA. THE NERN SC LOW WILL ACT TO

ENHANCE LOW LEVEL SHEAR OVER NERN SC AND ERN NC AND...ANY

WATERSPOUTS FORMING OFFSHORE COULD POSE A THREAT AS THEY MOVE TOWARD

THE COAST WITHIN ELY LOW LEVEL FLOW ALONG THE TRACK OF THE SURFACE

LOW FROM NERN SC TO THE NC COAST."

[HurricaneJosh]

The thing off SC needs to dry up and die-- we've already filled our quota of high-latitude crap systems for 2012.

Invest 99L needs to stay on a N-of-due-W course and chill out until it hits the NW Caribbean-- where it then explodes.

Thx.

[Superstorm93]

The thing off SC needs to dry up and die-- we've already filled our quota of high-latitude crap systems for 2012.

Invest 99L needs to stay on a N-of-due-W course and chill out until it hits the NW Caribbean-- where it should explode.

Thx.

18z ensembles like the SE coast.

[PSUBlizzicane2007]

The thing off SC needs to dry up and die-- we've already filled our quota of high-latitude crap systems for 2012.

Hush.

[CUmet]

Interesting differences between the ECMWF and GFS regarding 99L, with the ECMWF being much faster and quite a bit weaker. Consistent with this is the depiction of a much larger vortex tilt in the ECMWF than the GFS, shown below by a displacment between the 925 mb center and the 500 mb vorticity maximum.

ECMWF:

GFS:

After the above image in the GFS, the vortex tilt continues to increase and the system becomes gradually weaker with time. The presence of a tilted signature in both models, despite the SHIPS forecast of low shear over the next 5 days, suggests significant shear in the low-mid levels that isn't being captured by the 850-200 mb shear metric.

[HurricaneJosh]

Cool. Weak is good in these initial stages; as Jorge reminded me, it'll get further W that way. A sexy fish won't do us any good!

[phil882]

Interesting differences between the ECMWF and GFS regarding 99L, with the ECMWF being much faster and quite a bit weaker. Consistent with this is the depiction of a much larger vortex tilt in the ECMWF than the GFS, shown below by a displacment between the 925 mb center and the 500 mb vorticity maximum.

After the above image in the GFS, the vortex tilt continues to increase and the system becomes gradually weaker with time. The presence of a tilted signature in both models, despite the SHIPS forecast of low shear over the next 5 days, suggests significant shear in the low-mid levels that isn't being captured by the 850-200 mb shear metric.

Good point! The fact that both models show a tilted system is cause for concern for those rooting for TCG. It is interesting that the 12z GFS run was the first to show a more tilted solution in the medium range, with the 00z and 06z runs showed a more vertically aligned disturbance that moved into the Caribbean.

Another caveat that the models likely won't be handling well is the progression of a significant convectively coupled kelvin wave (CCKW). Mike Ventrice's Velocity Potential maps on the Kelvin Wave band show this feature well (in blue and purple) moving across the East Pacific over the last 3-5 days. This should be moving into the Atlantic basin over the next 24-48 hours and will likely help to aid in convective development with 99L. Typically behind CCKWs we also see enhanced upper level easterly flow. This might be a positive factor in the developmental prospects for 99L.

http://www.atmos.alb...l_analyses.html

[QVectorman]

Good point! The fact that both models show a tilted system is cause for concern for those rooting for TCG. It is interesting that the 12z GFS run was the first to show a more tilted solution in the medium range, with the 00z and 06z runs showed a more vertically aligned disturbance that moved into the Caribbean.

Another caveat that the models likely won't be handling well is the progression of a significant convectively coupled kelvin wave (CCKW). Mike Ventrice's Velocity Potential maps on the Kelvin Wave band show this feature well (in blue and purple) moving across the East Pacific over the last 3-5 days. This should be moving into the Atlantic basin over the next 24-48 hours and will likely help to aid in convective development with 99L. Typically behind CCKWs we also see enhanced upper level easterly flow. This might be a positive factor in the developmental prospects for 99L.

http://www.atmos.alb...l_analyses.html

Phil I have been watching that analyses since Mike mentioned it. I was under the impression from the information Mike supplied the last time it passed over the Atlantic was that it impeded development under it's core and slightly ahead of it and enhanced it behind the last contour...or is it enhancement after the core of the CCKW passes. Am I correctly understanding how the CCKW works from both of your descriptions?

[phil882]

Phil I have been watching that analyses since Mike mentioned it. I was under the impression from the information Mike supplied the last time it passed over the Atlantic was that it impeded development under it's core and slightly ahead of it and enhanced it behind the last contour...or is it enhancement after the core of the CCKW passes. Am I correctly understanding how the CCKW works from both of your descriptions?

You can actually look at a CCKW enhancing the probabilities for TCG in three different ways. I'll try to explain each one. For each example, lets refer to figure 6 from Straub and Kiladis (2002). Note that in the typical CCKW the wave is tilted vertically, with the shallow convective elements associated with surface convergence leading the wave with the divergent outflow of the stratiform precipitation following behind. Thus the circulation you can expect to see with a Kelvin (typically centered over the equator) should look like this.

1. Enhanced Convection with disturbance

This one should be simple to understand. When you get increased convergence at the surface, the result is often more convective development. Thus tropical disturbances that are lacking in convection can be aided by this larger scale kelvin wave which provides synoptic scale lift through convergence.

2. Lower Vertical Wind shear (depending on the region) behind a CCKW

Again given the vertical structure of the kelvin wave illustrated above, the backside of a CCKW typically results in upper level easterly flow and lower level westerly flow anomalies. For the Atlantic basin, most waves that struggle to develop in the face of a mid-latitude trough have difficulty developing due to westerly vertical wind shear. Such a configuration illustrated in the wake of a CCKW would reduce this westerly shear in theory. Note however if a system is already under a easterly shear regime this configuration would actually increase the easterly shear (anomalous westerly low level flow vs. anomalous easterly upper level flow). For 99L the main question is if westerly shear will decouple the low/mid-level circulation centers of the disturbance. The passage of a CCKW would aid in limiting this westerly shear.

3. Enhanced shear vorticity behind a CCKW

One thing that is mentioned less often with CCKW is that their theoretical structure bases the maximum wind anomalies at the equator. Most equatorial waves are constrained at the equator by definition with their influence weakening as you go further and further poleward. If the maximum low-level easterly flow is centered at the equator with weakening low-level easterly flow as you increase poleward. This jet maximum at the equator would then allow for cyclonic vorticity to occur merely by the weakening winds as you increase with latitude.

So you are mostly correct, the most favorable regime is typically at the apex of the CCKW and behind it, with the most unfavorable conditions in the subsiding phase of a CCKW (the orange/red contours in the loop I showed before) and just past it. However, #2 often depends on the prevailing wind shear typically experienced over the given basin. As long as you understand the structure of a CCKW its easy to understand their potential role of aiding vs. detracting from a disturbances organization/convection.

[HurricaneJosh]

By the way, things are status quo with the 8 pm EDT TWO.

[Ed Lizard]

By the way, things are status quo with the 8 pm PDT TWO.

Fairly unenthusiastic write up in tropical discussion, and it appears they've skipped the 12Z GFDL and HWRF cycles, judging from the FSU model page.

TROPICAL WAVE IS ALONG 17N36W TO A 1009 MB LOW AT 9N36W. THE

WAVE/LOW IS MOVING W AT ABOUT 10-15 KT. THE WAVE IS FAIRLY LOW

AMPLITUDE WITH A WEAK SIGNAL IN TOTAL PRECIPITABLE WATER.

HOWEVER...AN ANALYSIS OF THE SAHARAN AIR LAYER SHOWS A CLEARING

IN THE WIDESPREAD DUST NEAR THE WAVE AXIS INDICATING ITS

PRESENCE. THE SURFACE LOW IS EMBEDDED WITHIN THE MONSOON TROUGH

AND HAS BEEN FOR THE PAST SEVERAL DAYS. MODEL GUIDANCE INDICATES

THAT THE LOW WILL PERSIST FOR THE NEXT FEW DAYS AND THE SYSTEM

WILL BE MONITORED FOR POSSIBLE DEVELOPMENT.

CURRENTLY...SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS

LIMITED TO THE MONSOON TROUGH REGION FROM 6N-10N BETWEEN 35W-41W.

[icebreaker5221]

By the way, things are status quo with the 8 pm PDT TWO.

Yup. Both with the lemon and the homebrew, despite 18Z GFS still developing 2 waves of low pressure off the SC/NC coast. Sure there's a chance neither will become anything based upon convective trends today with the first wave, and considering the fact that the second one doesn't even exist yet, but there's nonetheless a region of slightly lower pressures in an area detaching from the remnant cold front. I think there's still a good chance we see a flare-up again overnight, this time further north than last night (VA coast?), but time will tell.

[Amped]

Judging by the Euro i'd say lame cyclone or no cyclone.

[phil882]

Judging by the Euro i'd say lame cyclone or no cyclone.

The 00z run shows some signs of life, however, with a distinct closed circulation at 925 hPa and more vertical coherence than we saw at 12z. This is pointing towards possible TCG around the 36-72 hour mark alongside the GFS. Like the GFS though, it shows the system opening up as it approaches the Caribbean, possibly due to the low/mid level flow accelerating faster than the upper level flow.

[QVectorman]

You can actually look at a CCKW enhancing the probabilities for TCG in three different ways. I'll try to explain each one. For each example, lets refer to figure 6 from Straub and Kiladis (2002). Note that in the typical CCKW the wave is tilted vertically, with the shallow convective elements associated with surface convergence leading the wave with the divergent outflow of the stratiform precipitation following behind. Thus the circulation you can expect to see with a Kelvin (typically centered over the equator) should look like this.

1. Enhanced Convection with disturbance

This one should be simple to understand. When you get increased convergence at the surface, the result is often more convective development. Thus tropical disturbances that are lacking in convection can be aided by this larger scale kelvin wave which provides synoptic scale lift through convergence.

2. Lower Vertical Wind shear (depending on the region) behind a CCKW

Again given the vertical structure of the kelvin wave illustrated above, the backside of a CCKW typically results in upper level easterly flow and lower level westerly flow anomalies. For the Atlantic basin, most waves that struggle to develop in the face of a mid-latitude trough have difficulty developing due to westerly vertical wind shear. Such a configuration illustrated in the wake of a CCKW would reduce this westerly shear in theory. Note however if a system is already under a easterly shear regime this configuration would actually increase the easterly shear (anomalous westerly low level flow vs. anomalous easterly upper level flow). For 99L the main question is if westerly shear will decouple the low/mid-level circulation centers of the disturbance. The passage of a CCKW would aid in limiting this westerly shear.

3. Enhanced shear vorticity behind a CCKW

One thing that is mentioned less often with CCKW is that their theoretical structure bases the maximum wind anomalies at the equator. Most equatorial waves are constrained at the equator by definition with their influence weakening as you go further and further poleward. If the maximum low-level easterly flow is centered at the equator with weakening low-level easterly flow as you increase poleward. This jet maximum at the equator would then allow for cyclonic vorticity to occur merely by the weakening winds as you increase with latitude.

So you are mostly correct, the most favorable regime is typically at the apex of the CCKW and behind it, with the most unfavorable conditions in the subsiding phase of a CCKW (the orange/red contours in the loop I showed before) and just past it. However, #2 often depends on the prevailing wind shear typically experienced over the given basin. As long as you understand the structure of a CCKW its easy to understand their potential role of aiding vs. detracting from a disturbances organization/convection.

wow awesome. Thanks for that!

[Superstorm93]

Despite being strongly embedded in the monsoon trof, 99L seems to have organized some last night.

The NHC either had trouble with their ATCF database or they didn't want to run the models last night, but the storm-specefic models just flowed in. Looks like a bit more of a Caribbean Cruiser (regardless of development).

[MJO812]

Here are the GGEM Ensembles. Some interesting scenarios.

http://www.weatheroffice.gc.ca/ensemble/charts_e.html?Hour=228&Day=0&RunTime=00&Type=pnm

[Superstorm93]

Here are the GGEM Ensembles. Some interesting scenarios.

http://www.weatherof...ime=00&Type=pnm

[Bryan Wood]

Looks like a Bastardi special.....how long before we see it on his Twitter?

[am19psu]

Can this be the last time someone posts a GGEM ensemble in the tropical threads? Thx.

[nycsnow]

Looks like a Bastardi special.....how long before we see it on his Twitter?

To busy on his global warming rants