Atlantic Tropical Action 2014

[Ground Scouring]

Yea lets predict no capeverde hurricanes in mid June. June TC's are rare and in all honest have no say in what the rest of the season might look like. I will say waters as of today across the mdr are quiet cool but in good faith should warm by mid aug. Major hurricanes can still occur during the worst of el ninos. Think positive :0)

Conditions have been so hostile the past few seasons that even homegrown systems didn't amount to much (other than Sandy). I was never speaking only of CV development when I said conditions would be hostile, period. Anything that forms this year, given the expected level of shear across the basin, will be either weak or short lived (or a high-latitude fish-spinner). The no-major-landfalls streak will continue. As for the possible upcoming system, it will be a rather sloppy, sheared TC at best, unlikely to be chaseable, with the strongest winds SE of the (offshore) center.

[wxtrackercody]

Not quite... Beryl was a tropical transition case that transitioned to a tropical cyclone from an initial baroclinic cyclone. What the ECMWF and GFS are suggesting is a remnant low-level vortex that originates from a MCS that propagates offshore. In fact the GFS traces the vorticity back to the big blow up of convection that resulted in an MCS in the NW Gulf of Mexico this afternoon.

 

http://www.tropicaltidbits.com/analysis/models/gfs/2014062518/gfs_z850_vort_watl.html

 

We have to watch though, because global models are known to spin up spurious vorticity that isn't realistic via the simplifed cummulus scheme modifying the heating profile of the atmosphere.

Nothing unrealistic this time.

 

[IsentropicLift]

The 12z ECMWF still develops a TC or Sub-TC near the Carolina coast early next week before tracking just offshore Wed-Sat. Pretty much follows the Gulf Stream all the way up the coast.

 

The 12z GGEM has the feature which sits and spins off the east coast before finally getting picked up by a trough late next week.

[icebreaker5221]

To follow up on today's conversation... You would be surprised to find out how many TCs do not originate from features we consider "tropical" In fact, baroclinic pathways are quite common.

 

For example, the three strongest hurricanes of the 2005 hurricane season all had non-tropical originating disturbances with some baroclinicity (Katrina 2005, Rita 2005, Wilma 2005). It's shortsighted to think that just because the MDR might be facing higher than normal shear this year that we can't get a decent TC in the subtropics. 

 

Now I'm not arguing for an active hurricane season (I am firmly in the pessimistic camp), but "home brew" type disturbances often can be just and impressive as those famed Cape Verde TCs. 

 

I think it's a bit misleading to say that Katrina, Rita and Wilma all had non-tropical originating disturbances.  Low-level vorticity associated with Rita definitely originated from an easterly wave that received the convective-boost needed to become a TD once it began interacting with a region of enhanced UL divergence courtesy a PV tail / trough breakoff, but there was definitely a pre-existing purely tropical surface trough.  The genesis of Wilma cannot be attributed to an easterly wave, although the non-tropical trough to the north was probably only a piece of the equation.  I would have to check again, but I believe Katrina was something similar to Rita. 

 

I'm definitely not disagreeing with your main points though, that {A} many TCs originate from non-tropical origins, and {B} that trough-interaction isn't necessarily a bad thing and can actually aid in the genesis process. 

[phil882]

I think it's a bit misleading to say that Katrina, Rita and Wilma all had non-tropical originating disturbances.  Low-level vorticity associated with Rita definitely originated from an easterly wave that received the convective-boost needed to become a TD once it began interacting with a region of enhanced UL divergence courtesy a PV tail / trough breakoff, but there was definitely a pre-existing purely tropical surface trough.  The genesis of Wilma cannot be attributed to an easterly wave, although the non-tropical trough to the north was probably only a piece of the equation.  I would have to check again, but I believe Katrina was something similar to Rita. 

 

I'm definitely not disagreeing with your main points though, that {A} many TCs originate from non-tropical origins, and {B} that trough-interaction isn't necessarily a bad thing and can actually aid in the genesis process. 

 

Good points Will. I think I should have been more clear that the non-tropical origination disturbances were not the primary piece that resulted in TCG, but that there needed to be some sort of tropical-mid-latitude interaction which then sparked TCG.

 

Katrina and Rita definitely had AEW's that were trackable before interacting with upper-level troughs (PV tails ect.) which originated in the mid-latitudes and were pushed equatorward by anticyclonic wavebreaking.

 

However, its difficult to say what was more important, the originating AEW or the mid-latitude trough, which can provide large scale vertical ascent due to diffluence which generates more low-level vorticity via convection. If a trough is strong, its rossby penetration depth can allow the cyclonic vortex to reach the surface, which provides low level vorticity through that mechanism. If you have a weak AEW that then undergoes a trough interaction, if the trough generates more low-level vorticity than what the original AEW contained, can you can it was the primary player in the system's genesis? 

 

I guess my point I was trying to make is that you don't need systems developing deep in the MDR to have a significant TC. In fact a lot of 2005's TC activity occurred outside of the MDR and that was the most active season on record. 

 

In general though I think the role that non-tropical entities play in the genesis of TCs is a pretty underemphasized area of research that should be looked at more closely. 

[phil882]

Nothing unrealistic this time.

 

 

 

Yep, it looks like a real feature... the ECMWF has gotten more aggressive about TCG in the 4-5 day range. Finally something to watch

[hurricaneman]

The thing I have to wonder is if the area over Alabama combines with the ULL to initiate cyclogenesis south of South Carolina or if its completely just the low over Alabama

[phil882]

The thing I have to wonder is if the area over Alabama combines with the ULL to initiate cyclogenesis south of South Carolina or if its completely just the low over Alabama

 

What ULL are you referring to? The ECMWF last week had a tropical transition scenario off the east coast involving an upper-level trough, but this is now a completely different setup, with upper-level ridging present over the MCV moving offshore for the next 4-6 days. 

 

So to answer your question its primarily the low-level vortex over the southeast right now.

[hurricaneman]

What ULL are you referring to? The ECMWF last week had a tropical transition scenario off the east coast involving an upper-level trough, but this is now a completely different setup, with upper-level ridging present over the MCV moving offshore for the next 4-6 days. 

 

So to answer your question its primarily the low-level vortex over the southeast right now.

The ULL between Bermuda and the Bahamas

[IsentropicLift]

FWIW every 15z SREF member has development within 48 hours.

[NaoPos]

FWIW every 15z SREF member has development within 48 hours.

GFS through 51 looks meager..

[phil882]

The ULL between Bermuda and the Bahamas

 

At best that will probably only play a minor role in enhancing upper tropospheric outflow over the MCS moving off the east coast. There are actually two ULLs, one just west of Bermuda, and one further southwest almost over the Bahamas. The amount of convection occurring today over this region will likely result in some PV destruction in the upper-levels to the point that these upper-level lows will probably be non factors by the time the MCV emerges off the coast. 

 

FWIW every 15z SREF member has development within 48 hours.

 

SREF = NAM when looking at the tropics. Wouldn't recommend using even for short term TC forecasts.

 

If you have to look at them tough, the ARW members tend to be more reliable than the NMM members in the tropics. The NMM members share the same physics core as the NAM, while the ARW use a core developed by the folks at NCAR. 

 

GFS through 51 looks meager..

 

 

The GFS is definitely not as optimistic about genesis in comparison to the ECMWF... however it does have the feature offshore at 42 hours under anticyclonic flow at 200 hPa.

 

[phil882]

If the Global Models are correct... the decaying MCV should get a good convective burst this evening since its in good position within the right entrance region of a jet streak to its northeast. Deep convection already developing nearby in NC/SC. The ECMWF for the 3-4th consecutive run has a weak TD/TS in the medium range, so I'd say confidence is slowly increasing for the potential of TCG off the east coast later this weekend into early next week.

 

 

[wxmx]

10% Lemon...

 

It looks kind of weird to see a lemon inland

[wxmeddler]

Pretty obvious here:

http://climate.cod.edu/flanis/satellite/1km/index.php?type=Carolinas-vis-48

[phil882]

While the surface circulation is broad and diffuse... its still showing up on the surface METAR plots, with westerlies in SC and easterlies in NC... though will need some deeper convection to develop a vertically stacked circulation.

 

 

SSTs are in the 27-28 C range which is plenty warm... if its got enough of a llc when it moves offshore tomorrow, I don't think the shear will be detrimental enough to prevent slow development.

 

[Ground Scouring]

Finally, something to keep an eye on. 

If you're thinking about possible effects in the Outer Banks or the Mid-Atlantic beaches, forget it. This system's going to be weak at best and should scoot NE over the Gulf Stream toward the Canadian Maritimes. I expect a sheared, asymmetric, 45-kt TC at most (if anything forms). If DT's theory is right, the first track of the season could indicate a seasonal trend. A track NE out to sea or ern Canada would favor a fishy year without major (meaning hurricane) U.S. impacts.

[tmagan]

10% Lemon...

 

It looks kind of weird to see a lemon inland

atl_overview.gif

I thought they were going to go with the 5 day map this year.

[Srain]

I thought they were going to go with the 5 day map this year.

It has been 0% for a couple of days in the TWO.

[phil882]

I thought they were going to go with the 5 day map this year.

 

Just a few more days! 

 

"The new 5-day GTWO, available for both the Atlantic and eastern North Pacific basins 

beginning July 1, will indicate the formation potential of individual disturbances during the 

next 5 days."

 

http://www.nhc.noaa.gov/news/20140320_pa_2014seasonChanges.pdf

 

By the way the 5 day outlook is up to 30%. 

[SnoSki14]

If you're thinking about possible effects in the Outer Banks or the Mid-Atlantic beaches, forget it. This system's going to be weak at best and should scoot NE over the Gulf Stream toward the Canadian Maritimes. I expect a sheared, asymmetric, 45-kt TC at most (if anything forms). If DT's theory is right, the first track of the season could indicate a seasonal trend. A track NE out to sea or ern Canada would favor a fishy year without major (meaning hurricane) U.S. impacts.

Actually the weak steering currents would favor a southerly to southwesterly drift most likely into the SE coast of say Florida/Georgia. I don't think it would matter right now what the track is right now compared to later. Given the hostile MDR, development would more likely be closer to shore or homegrown thus increasing the landfall risk unless you're talking about a storm developing well north in the subtropics. The big question will be how much activity will we really see given that this year looks a lot worse than last.

[Ground Scouring]

Actually the weak steering currents would favor a southerly to southwesterly drift most likely into the SE coast of say Florida/Georgia. I don't think it would matter right now what the track is right now compared to later. Given the hostile MDR, development would more likely be closer to shore or homegrown thus increasing the landfall risk unless you're talking about a storm developing well north in the subtropics. The big question will be how much activity will we really see given that this year looks a lot worse than last.

The weak steering currents are only within the first three days. And if you look at the low-level steering, there is no mechanism to push the system SW into FL or GA. The predominant trend in the ECMWF and GFS ensembles is a slow drift/stationary movement off the SE coast through day 4, when a deepening longwave trough over Hudson Bay imparts a steady acceleration off to the NE, well offshore of the East Coast. There is nothing to substantiate a landfalling impact anywhere other than in the Canadian Maritimes (as an ET low). Re: homegrown development, while the hostile MDR would seem to favor homegrown systems in the Gulf/Bahamas, an east-based Niño would also increase shear in those areas as well as in the MDR, so even homegrown development is unlikely (as it was last season, given all the shear in the Caribbean/GOM/SW Atlantic)--unless a TC develops over the Gulf Stream in the region above 30°N. And even in that case, the existence of a likely trough off the East Coast in August/September would take any homegrown development NE into the Canadian Maritimes or out to sea.

[phil882]

The weak steering currents are only within the first three days. And if you look at the low-level steering, there is no mechanism to push the system SW into FL or GA. The predominant trend in the ECMWF and GFS ensembles is a slow drift/stationary movement off the SE coast through day 4, when a deepening longwave trough over Hudson Bay imparts a steady acceleration off to the NE, well offshore of the East Coast. There is nothing to substantiate a landfalling impact anywhere other than in the Canadian Maritimes (as an ET low). Re: homegrown development, while the hostile MDR would seem to favor homegrown systems in the Gulf/Bahamas, an east-based Niño would also increase shear in those areas as well as in the MDR, so even homegrown development is unlikely (as it was last season, given all the shear in the Caribbean/GOM/SW Atlantic)--unless a TC develops over the Gulf Stream in the region above 30°N. And even in that case, the existence of a likely trough off the East Coast in August/September would take any homegrown development NE into the Canadian Maritimes or out to sea.

 

I think its a little early to make that call... the system is very diffuse right now, and whether or not it gets picked up by the upper-level trough next week will probably be dictated by how far south it moves in the next 36-48 hours. The N-S oriented ridging to its west is strongest in the low-levels, so actually a weaker system that doesn't develop right away would be more prone to escaping further south. The shear vector will also be out of the north, so we will likely also see convection displaced south of the low-level circulation, and northerly sheared TCs can oftentimes redevelop south under the convection via vortex stretching of the pre-existing circulation closer to the convection (see Cristobal 2002).

[phil882]

Looks like the broad circulation has slipped offshore... lots of towers going up all over the place right now. It picked the right time to move offshore for the oceanic diurnal max. 

 

[wxmeddler]

Looks like the broad circulation has slipped offshore... lots of towers going up all over the place right now. It picked the right time to move offshore for the oceanic diurnal max. 

 

I'm watching it on GR3, multiple towers 50k+ right now. The cell 115mi E of Hilton Head bounced back a 60k top (18dbz) for 2 scans about 15 min ago.

[phil882]

I'm watching it on GR3, multiple towers 50k+ right now. The cell 115mi E of Hilton Head bounced back a 60k top (18dbz) for 2 scans about 15 min ago.

 

Another good thing for the system as its moving offshore is that its got a nice plume of decent moisture around it (~50 mm) which should be enough to sustain moist convection (as is occurring tonight)

 

[wxmeddler]

Another good thing for the system as its moving offshore is that its got a nice plume of decent moisture around it (~50 mm) which should be enough to sustain moist convection (as is occurring tonight)

 

Yep, lots of moisture available to it. The dual-pol returns are quite impressive too. I'm seeing +1 to+2 db ZDR and +2 to +3°/km KDP returns at 20kft, which is -12°C  @ 450mb via RAP. That's a lot of latent heat being released in those towers.

[phil882]

Yep, lots of moisture available to it. The dual-pol returns are quite impressive too. I'm seeing +1 to+2 db ZDR and +2 to +3°/km KDP returns at 20kft, which is -12°C  @ 450mb via RAP. That's a lot of latent heat being released in those towers.

 

Yep... and that should begin the PV displacement, enhancing the low-level cyclonic vorticity below the level of heating while building upper-level anticyclonic flow above the level of maximum heating. The fact that this system is as convectively active tonight is a very good sign that the environment is moist and healthy for the proto vortex. 

 

Its worth noting the GFS had a weaker convective signature as the vortex moved offshore... see image below. Coldest cloud tops are in the -70 C range while the GFS only had a small region of -40 to -50 C tops. Of course the horizontal resolution of the GFS (~27 km here) is substantially less than satellite imagery, but this might be a case where the GFS is under-doing the amount of LHR unlike situations where it suffers from convective feedback. 

 

 

Compare to reality

 

[phil882]

00Z ECWMF is coming in stronger with the mid-level vortex... and its doing a MUCH better job with the current MCS ongoing offshore of the Carolinas. Its also further west and closer the Florida coast around 3 days from now.

 

This system looks like a TD/TS by the end of the weekend according to the ECMWF.

 

[phil882]

Up to 30% and 50% respectively for 48 hour and 5 day outlooks. Likely will get an invest designation later today.

 

1. A weak low pressure system located just off the coast of South
Carolina is producing an area of disorganized showers and
thunderstorms. Environmental conditions are expected to remain
conducive for gradual development of this system while
it drifts southward during the next few days.
* Formation chance through 48 hours...medium...30 percent.
* Formation chance through 5 days...medium...50 percent.