Atlantic Tropical Action 2012 - Part I

[wxmx]

Hasn't the NAO been negative since May 27? I see what you mean in that it's been variable tho, ranging from slightly negative to very negative, and also changing from west-based to east-based.

Talking about 1 day NAO, from raleighwx site, not the 3-day centered filter...even the 3-day centered filter gfs forecast peaks at neutral (very slightly positive) in a few days, before dipping back into the negatives...we might see the first positive reading since May, but it's so borderline, and bias has been for higher numbers than what have actually occurred, that it might as well stay negative.

[Ed Lizard]

Looks like NAO is going to fluctuate quite a bit over the next 10 days. Slightly neg now, then neutral, positive, probably back to neg. The pattern so far this July would have been pretty good for a slow recurve into the SE coast or maybe the Gulf, but with the variability of the NAO along with how much the pattern changed over the SE US from Jun to Jul probably gives even less confidence in a persistence forecast than usual. I agree tho that we haven't seen anything suggesting an east coast landfall so far.

McTaggart-Cowan et. al 2008 (http://journals.amet...5/2007MWR2245.1) looks at TC genesis climatology by location. Broadly speaking, non-baroclinic and LL-baroclinic are "tropical" systems while the others are not. Looks like almost half of the genesis events in the SE Gulf are considered tropical, while about 85% of genesis in the NW Gulf is either tropical transition or transient trough interaction.

Silly question, actually confusion induced, what is the source of the low level baroclinicity once well West of the discussed difference in temperatures near the coast due to relatively cooler SSTs and African air with some SAL? (The discussion mentions Central America, the graphic implies it extends across the basin) The graphic seems to imply this is a source of cyclones all the way through the MDR. And I'm wondering if the low level baroclinic /mid level easterly jet systems that don't develop immediately are the source of the "traditional tropical development" in the Central/Western MDR attributed to (and I quote) involving MCV development, hot tower spinup, vortex merger, stability profile modification, or surface flux enhancement, and likely a combination of several or all of these models?

I understand the gist of the following paragraph, but the sentence bolded confuses me, it seems backwards. Forgive my ignorance. This might be more a met 101 subforum thing, but we're already discussing this.

In addition to the cyclogenetic properties of ascent through lower-level convergence and stretching, sustained uplift increases the midlevel relative humidity by adjusting the temperature profile toward dry adiabatic. This midlevel moistening limits the effectiveness of mixing-induced downdrafts in establishing a near-surface cold pool that reduces the efficiency of the convective element (Maddox 1983).

[icebreaker5221]

Silly question, actually confusion induced, what is the source of the low level baroclinicity once well West of the discussed difference in temperatures near the coast due to relatively cooler SSTs and African air with some SAL? (The discussion mentions Central America, the graphic implies it extends across the basin) The graphic seems to imply this is a source of cyclones all the way through the MDR. And I'm wondering if the low level baroclinic /mid level easterly jet systems that don't develop immediately are the source of the "traditional tropical development" in the Central/Western MDR attributed to (and I quote) involving MCV development, hot tower spinup, vortex merger, stability profile modification, or surface flux enhancement, and likely a combination of several or all of these models?

Even over the MDR, the SAL air remains warmer and drier than non-SAL air to the south. Albeit weak, a north-south temperature gradient remains even several thousand kilometers over the open ocean. Remember, these cases are associated with weak baroclinicity. The moderate and strong baroclinic cases are almost always of non-tropical origin.

You're right that based upon their criterion for identifying genesis events, it's likely that easterly waves that would have been LL baroclinic but lose their baroclincity by the time the reach the Caribbean would fall into the traditional tropical development category.

I understand the gist of the following paragraph, but the sentence bolded confuses me, it seems backwards. Forgive my ignorance. This might be more a met 101 subforum thing, but we're already discussing this.

In addition to the cyclogenetic properties of ascent through lower-level convergence and stretching, sustained uplift increases the midlevel relative humidity by adjusting the temperature profile toward dry adiabatic. This midlevel moistening limits the effectiveness of mixing-induced downdrafts in establishing a near-surface cold pool that reduces the efficiency of the convective element (Maddox 1983).

So, prior to the period of sustained uplift, the temperature profile over the tropics does not cool particularly quickly with height (lase rates are not particularly steep). As uplift commences, non-saturated parcels rise dry adiabatically to the LCL. If this is occurring on a sufficiently large scale, the environmental profile shifts closer to dry adiabatic, which equates to steeper lapse rates, cooler mid-level temperatures, lower saturation deficit, and therefore higher relative humidity.

Of course this process doesn't last long. Once the profile becomes saturated and deep convection commences, latent heating quickly warms the mid levels and a warm core starts to develop.

Edit: I think that explanation makes sense, but maybe I'll think about it some more tomorrow after some much needed sleep.

Edit 2: Sorry Adam if slightly OT. Figured it was relevant to genesis and it could slide while the tropics are so quiet.

[wxmx]

Some good news from model world, finally. The wave/low around 10N 40W stays alive in the 0z GFS and strengthens some just before entering the caribbean...then it decides to suicide while it island hops thru the Leeward islands...but at least there's a change.

[am19psu]

Edit: I think that explanation makes sense, but maybe I'll think about it some more tomorrow after some much needed sleep.

Edit 2: Sorry Adam if slightly OT. Figured it was relevant to genesis and it could slide while the tropics are so quiet.

Pffft, don't worry about it. This is exactly the kind of discussion we want to foster and encourage in this thread, particularly when it is quiet.

[Superstorm93]

Very intense MCV over Africa. It's a shame that this will pull a "Das Poof" as soon as it touches the Atlantic.

Really has some nice motion to it.

[Srain]

While everyone is monitoring the MDR, it still remains my hunch that the Gulf will offer a surprise or two before all is said and done. This repeating pattern of frontal boundaries sagging S into the Tennessee Valley and MCS's dropping S into the E/Central Gulf may well allow for a W tracking system to develop beneath the Central US Ridge during August. We will see.

[am19psu]

While everyone is monitoring the MDR, it still remains my hunch that the Gulf will offer a surprise or two before all is said and done. This repeating pattern of frontal boundaries sagging S into the Tennessee Valley and MCS's dropping S into the E/Central Gulf may well allow for a W tracking system to develop beneath the Central US Ridge during August. We will see.

Rainer

[Ed Lizard]

Rainer

Steve experienced a marginal major from such a scenario back when Ms. Pacman was popular, and I, for one, refuse to discourage someone who shares my glass 5/132^nds optimism.

[Ed Lizard]

Very intense MCV over Africa. It's a shame that this will pull a "Das Poof" as soon as it touches the Atlantic.

Really has some nice motion to it.

Despite being surrounded by SAL, the wave around 45ºW still looks almost decent. Would not be completely surprised if it doesn't try to develop in the EastPac, although CFS forecast 200 mb chi gets ugly in the EastPac about when it would arrive.

To bad the next little cluster is 20º away from your nicely animated bomb, something arriving sooner might get some help from having that as a lead SAL block.

[Srain]

Rainer

Could be. Jack and I discussed this possibility and one cannot discount a quick spin up ala Alicia to break this Plains drought as it did in 1983...

Hurricane Alicia ended a 3 year and 8 day "hurricane drought" for the continental United States,

which was the longest such period in the 20th century. The low that became Alicia formed from a

mesoscale convective system that developed on the tail end of a frontal zone just offshore the central

Gulf coast. The system moved around the southwest periphery of the subtropical ridge and intensified

at the rate of one millibar per hour into a tropical storm on the 15th and a hurricane on the 16th. As the

ridge moved eastward, Alicia turned northwest to the west of Galveston and Houston, Texas, striking the

Lone State State as a category 3 hurricane. Helping to break drought conditions across the southern

Plains, Alicia dropped moderate to heavy rains across portions of Texas and Oklahoma before its surface

circulation began to open up across the central Plains on the 20th.

[am19psu]

Could be. Jack and I duscussed this possibility and one cannot discount a quick spin up ala Alicia to break this Plains drought as it did in 1983...

Can't be discounted, but a rainer is much more likely.

[Ed Lizard]

Erin wasn't purely non-tropical in origin, but it was a "rainier", and I don't have the elitist 'Major Hurricane or Nothing' approach, and have been able to enjoy storms like Frances, Fay and Erin, or Cat 1s like Claudette. Plus, obviously, as a fan of food, I'm hoping the corn crop can be salvaged.

[Srain]

Can't be discounted, but a rainer is much more likely.

Now this was a rainer...probably still holds the record for the most rainfall in a 24 hour period...

[HurricaneJosh]

Edit 2: Sorry Adam if slightly OT. Figured it was relevant to genesis and it could slide while the tropics are so quiet.

Totally cool. Nothing is really off topic in this thread-- it's deliberately wide-ranging and casual. And I appreciate your insights.

Pffft, don't worry about it. This is exactly the kind of discussion we want to foster and encourage in this thread, particularly when it is quiet.

Si.

[HurricaneJosh]

Very intense MCV over Africa. It's a shame that this will pull a "Das Poof" as soon as it touches the Atlantic.

Really has some nice motion to it.

It's awesome-looking, but the latitude is kinda high for my tastes. Something coming off Africa that far N would have a lot of trouble making it across. But if you're a seafood lover, I guess it's cool.

[Ed Lizard]

Quiet time posting- no idea if "Weather Research Center's "Orbital Cyclone Strike Index" made one of the early pages of this thread, and have chosen not to search for it. Sounds mildy J-Field-ish, the orbits of the planets affecting hurricanes, but their preseason forecast, in hindsight, of a slow season seems reasonable. Magazine article, 2010s will be slow for major storms in the Gulf, 2020s and 30s will be active. Again, it is based on planetary orbits, FWIW.

They have an article in Offshore Engineer ( a trade magazine, many of the articles read like advertisements for the service companies whose authors wrote them) not a peer reviewed journal like the JPT. Anyway, they have developed something called the Freeman-Hasling Potential Scale. Little description given, except it obviously involves size of the hurricane force wind fields.

Found more in this 4 Meg PDF. I have some questions about Table 4.

Not in the pdf, in the magazine, a measure of the progress of Gulf offshore engineering. The 1948 Grande Isle hurricane destroyed 28.6% of the platforms in the Gulf (2 of 7), Ike only destroyed 1.6% of the platforms in the Gulf (59 of 3737)

[Ed Lizard]

While everyone is monitoring the MDR, it still remains my hunch that the Gulf will offer a surprise or two before all is said and done. This repeating pattern of frontal boundaries sagging S into the Tennessee Valley and MCS's dropping S into the E/Central Gulf may well allow for a W tracking system to develop beneath the Central US Ridge during August. We will see.

Too bad its 14 days out and probably not going to happen, but the new GFS tries to develop something on the tail end of a rotting front near Pensacola before moving it inland. Never quite gets an isobar closed at the surface, but it tries.

And one of the 20 GFS perturbations on the 18Z GFS ensembles actually was just starting to recurve a 1008 mb long tracker East of the Bahamas. Doesn't sound like much, but more than several previous ensemble runs did.

Obviously, still waiting on the Hour 360 GFS Cat 5 bearing down on ECFL.

Baby steps.

[uncle W]

Too bad its 14 days out and probably not going to happen, but the new GFS tries to develop something on the tail end of a rotting front near Pensacola before moving it inland. Never quite gets an isobar closed at the surface, but it tries.

And one of the 20 GFS perturbations on the 18Z GFS ensembles actually was just starting to recurve a 1008 mb long tracker East of the Bahamas. Doesn't sound like much, but more than several previous ensemble runs did.

Obviously, still waiting on the Hour 360 GFS Cat 5 bearing down on ECFL.

Baby steps.

just what northern Florida needs...Another soaker...I hope it's just fantasy...

[Ed Lizard]

just what northern Florida needs...Another soaker...I hope it's just fantasy...

Judging by the spread, NAEFS probably has a member or two that develops something short term in the Gulf from the storms moving offshore and quickly moves it inland, and again, judging by spread (nothing obvious on the means), has a system cross the Yucatan and head for the border day 10-12

No development on the Euro, but it tracks a wave, I think yesterday's African bomb, all the way across the Atlantic, perhaps to meet the East Coast trough. Perhaps the relative lack of development will let it slide to towards Florida if the Euro forecast through Day 10 is correct.

That could be whatever the random Canadian member of the NAEFS is picking up for the TX/MX border region...

As I said, baby steps, at least hints in the models something could happen.

[bluewave]

You can see he SAL pushing west across the Atlantic.

[phil882]

If that convection near Louisiana can slide just another 100+ km southward, there is some potential for development. While the global models aren't very optimistic, this is primarily contingent on the system staying stationary today or moving northward back onshore. The ECMWF actually shows a pretty decent 500 hPa vorticity signature over LA after this feature moves onshore. If this is situated about 100 km further southward there is some potential for development.

One model that is suggesting the Global models might not be the correct solution is the HRRR. The model is doing a decent job with the convective signature of the system today, and it shows in the short term the 500 hPa vorticity (associated with diabatic heating from convection) should be shifting southwestward as it feels the effects of northerly flow on the front edge of the strong mid-level ridge over the Midwest. The mid-level vortex that is spun up from the convection is thus located further south and under a favorable environment for development underneath the ridge.

[Srain]

^^

Edouard 2008 formed in a somewhat similar fashion. Needless to say we in the NW Gulf have been following the suspicious develops across Southern Louisiana the past couple of day.

[wxmx]

If that convection near Louisiana can slide just another 100+ km southward, there is some potential for development. While the global models aren't very optimistic, this is primarily contingent on the system staying stationary today or moving northward back onshore. The ECMWF actually shows a pretty decent 500 hPa vorticity signature over LA after this feature moves onshore. If this is situated about 100 km further southward there is some potential for development.

One model that is suggesting the Global models might not be the correct solution is the HRRR. The model is doing a decent job with the convective signature of the system today, and it shows in the short term the 500 hPa vorticity (associated with diabatic heating from convection) should be shifting southwestward as it feels the effects of northerly flow on the front edge of the strong mid-level ridge over the Midwest. The mid-level vortex that is spun up from the convection is thus located further south and under a favorable environment for development underneath the ridge.

Good post Phil, I was wondering the same thing... energy a little more to the south and/or a stronger ridge than progged in the CONUS midsection and things could get interesting.

[Ed Lizard]

I think I see a hint of an MCV pushing off Vermillion parish. Obviously, won't have time to do anything significant, but as long as it doesn't get named and ruin my 0/0/0, I have no issues with this trying to become a depression and give my sprinkler even more time off this month.

[phil882]

The vorticity with the remnant MCV is still visible as convection starts to fire back up further east. Could be an interesting day if convection continues to increase over the open waters. The HURR generally did a good job suggesting the convection would be able to fester over the open waters rather than over land like some of the global models were projecting yesterday.

A quick glance at the ECMWF this morning shows that the model has corrected its previous mistake and now shows a decent mid-level vorticity signature in the Gulf of Mexico. Its not significant enough to be a tropical cyclone, but the ECMWF keeps the vorticity over the GOM for 24-48 hours before landfall in Texas. There is a decent outflow jet to the southeast that might help to ventilate convection, so I'm a little perplexed why the ECMWF seems pretty bearish on development. I wouldn't be surprised if things end up a little more interesting than its current deterministic solution.

[Srain]

^^

Buoy data and early morning Hi Res Imagery suggest a broad low level circulation a couple of hundred miles S of Vermillion Parish. We'll see what the day brings and if deeper convection begins to fire. Pressures remain rather high, but with additional storms dropping S later today within the Slight Risk area note by the SPC, perhaps a bit more low level spin can develop and tighten up. This likely would be a rather slow process, though.

[wxmx]

Still some way to go...rather strong NErly shear is affecting the disturbance

[Ed Lizard]

^^

Buoy data and early morning Hi Res Imagery suggest a broad low level circulation a couple of hundred miles S of Vermillion Parish. We'll see what the day brings and if deeper convection begins to fire. Pressures remain rather high, but with additional storms dropping S later today within the Slight Risk area note by the SPC, perhaps a bit more low level spin can develop and tighten up. This likely would be a rather slow process, though.

People scoff at the NAM and Canadian as tropical guidance, but I specifically remember they were the first to pick up on Edouard, and neither is pocking up on whatever is in the Gulf. NAM is picking up something toward the end of the run that doesn't close a surface low coming from the Southeast, but unrelated to this.

Not a model hugger, but I'd like to see 1 model onboard.

[Srain]

The latest Eurosip seasonal data suggest that we may see an up tick in activity in the Western Basin as we head toward late August/Early September. I suspect Josh will have several opportunities for intercepts both along the W Coast of Mexico as well as Western/NW Gulf before this season is all said and done. We will see.