Atlantic Tropical Action 2014

[phil882]

Looks like new hot towers are going up near where the formative surface circulation is with nice curved bands organizing to the east... probably less than 24 hours away from genesis based on the increasingly impressive satellite presentation.

 

[phil882]

While all the focus is deservedly on 93L, the wave behind doesn't look too shabby. This is actually the feature the ECMWF had been suggesting would be a more impressive than 93L. Both the ECMWF and GFS suggest dry air / SAL get into its formative circulation before it has a chance to blossom. Still worth keeping an eye on it behind 93L, especially as a rather impressive CCKW keeps moving quickly through the Atlantic basin.

 

 

[Mike.Ventrice]

While all the focus is deservedly on 93L, the wave behind doesn't look too shabby. This is actually the feature the ECMWF had been suggesting would be a more impressive than 93L. Both the ECMWF and GFS suggest dry air / SAL get into its formative circulation before it has a chance to blossom. Still worth keeping an eye on it behind 93L, especially as a rather impressive CCKW keeps moving quickly through the Atlantic basin.

 

 

 

Attaboy Phil, attaboy. Been promoting this CCKW to TWC since last Tuesday.. If I had a link, I'd show you Norcross's segment explaining the increased odds this week due the strong CCKW+developing MJO that they put together to try help explain these events. Looks very similar to the 2006 Debby/Ernesto case

[wxtrackercody]

Already seeing new convective development over the low-level circulation:

 

 

NHC went 50% (for the 2-day window) at 8pm, but this already looks like a tropical depression, no?

[Sunny and Warm]

the GFS appears to be winning this battle for the moment, but Mother Nature is a tough teacher.

[Superstorm93]

Could see the NHC needing a special TWO by the time 11pm rolls around. 

 

 

Also have an ASCAT pass coming in now.

[Superstorm93]

[Kory]

Nice CDO developing on 93L this evening. 

 

http://rammb.cira.colostate.edu/products/tc_realtime/loop.asp?product=4kmirimg&storm_identifier=AL932014&starting_image=2014AL93_4KMIRIMG_201407281900.GIF

[Ground Scouring]

While all the focus is deservedly on 93L, the wave behind doesn't look too shabby. This is actually the feature the ECMWF had been suggesting would be a more impressive than 93L. Both the ECMWF and GFS suggest dry air / SAL get into its formative circulation before it has a chance to blossom. Still worth keeping an eye on it behind 93L, especially as a rather impressive CCKW keeps moving quickly through the Atlantic basin.

That one might have a better shot at threatening the U.S. down the road, given that the WAR will be rebuilding in eight to 10 days. But that's only if it survives the SAL, which seems unlikely. (Conditions otherwise look good for development as long as it briefly remains within the ITCZ.) 93L will be moving far too quickly for the ridge to build back in before recurvature. I'm thinking that unless we see more development before early September, the U.S. will probably escape as El Niño sets in/starts affecting the atmosphere by early September. This season will end early, in my opinion.

[JC-CT]

That one might have a better shot at threatening the U.S. down the road, given that the WAR will be rebuilding in eight to 10 days. But that's only if it survives the SAL, which seems unlikely. (Conditions otherwise look good for development as long as it briefly remains within the ITCZ.) 93L will be moving far too quickly for the ridge to build back in before recurvature. I'm thinking that unless we see more development before early September, the U.S. will probably escape as El Niño sets in/starts affecting the atmosphere by early September. This season will end early, in my opinion.

Lol I read your post quickly on mobile, without looking to see who the author was, then flipped back to the main forum navigation, then said to myself, "wait, Ground Scouring is that you?" And lo and behold!

[thewxmann]

That one might have a better shot at threatening the U.S. down the road, given that the WAR will be rebuilding in eight to 10 days. But that's only if it survives the SAL, which seems unlikely. (Conditions otherwise look good for development as long as it briefly remains within the ITCZ.) 93L will be moving far too quickly for the ridge to build back in before recurvature. I'm thinking that unless we see more development before early September, the U.S. will probably escape as El Niño sets in/starts affecting the atmosphere by early September. This season will end early, in my opinion.

 

We're thinking wayyyyy too far ahead here. Let's just focus on 93L and the system behind for now.

[Floydbuster]

Nice low shear environment currently over the top of it.

 

[Kory]

Models are trending weaker with this system.  Northeasterly shear is picking up ahead of the system, which may allow for some intrusion of dry air...looks like we're already beginning to see a little of that happening.  Not quite sure we'll see anything declared today despite how good this looked yesterday.  

[Snowman99]

LOT'S of Saharan dust in the Atlantic, chances of development of anything is quite low IMO.

[Ground Scouring]

Lol I read your post quickly on mobile, without looking to see who the author was, then flipped back to the main forum navigation, then said to myself, "wait, Ground Scouring is that you?" And lo and behold!

 

 

We're thinking wayyyyy too far ahead here. Let's just focus on 93L and the system behind for now.

You're both right…I was getting too far ahead of myself.

 

Re: 93L, low-level shear out of the ENE clearly is advecting dry air/SAL into the circulation, and the strengthening of the low-level easterlies is reducing low-level convergence--both of these factors, as expected, have reduced convection this morning. The ECMWF, despite its issues with developing TCs, seems to do quite well at forecasting the medium-range environment and intensity of a cyclone. That is why it is often the first to pick up on trends that the other models miss at first. Note how the dynamical models (the HWRF and the GFDL, for instance) are coming into line with the ECMWF re: a weaker 93L through the medium term. Even the GFS has backed off on the intensity over the next three days. A weaker 93L will move faster and will not be able to form as much of an UL anticyclone to offset the westerly shear it will encounter near the islands as it meets the MOT/TUTT--hence the weakening/opening up of the system on the ECMWF near the islands. Needless to say, this evolution would mean a track through the Leeward Islands and a collision course with Puerto Rico and Hispaniola, which would probably kill an already-feeble system.

[wxtrackercody]

The 12z GFS shows this deepening on approach to the northern Leeward Islands, but weakens it steadily thereafter. It eventually passes just northeast of the Bahamas as a strong wave.

 

A dramatic shift, to say the least.

[NJWxWatcher201]

I think were just lacking some convection at this point ...

 

http://www.ssd.noaa.gov/goes/east/tatl/flash-vis.html

 

A few hot towers go up and were golden. Hey, looks better than the "Arthur" image still pinned up on the front page.

[phil882]

The 12z GFS shows this deepening on approach to the northern Leeward Islands, but weakens it steadily thereafter. It eventually passes just northeast of the Bahamas as a strong wave.

 

A dramatic shift, to say the least.

 

Which is now remarkably close the ECMWF. As I mentioned yesterday, while the ECMWF may not have the best genesis track record, it tends to perform remarkably well post genesis often due to its superior convective scheme in the tropics. If we wanted to see a more GFS like solution the system was going to need to have blossoming convection today. That's obviously not the case, and a little bit of easterly shear has allowed the relatively dry air to its north and east to get advected into the core.

 

Yesterday the system had a significant moisture plume, but thats withered away today. In fact TD#2 had deeper convection than 93L did prior to genesis. The thing in 93L's favor though is that is has a larger surface circulation, from which it should still be able to to tap the moisture to its south in the ITCZ. I think the convection recovers somewhat tonight and we have a TD within the next 24 hours.

 

However, this hiccup in its convective development has implications when it reaches the edge of the stronger easterly flow near the lesser antilles. A stronger TC with active convection would be able to fight off the moderate westerly vertical wind shear the system will likely face. However, if its a weak TD/TS by the time it reaches this region (especially if the moisture plume associated with the system continues to shrink) its toast and will likely have a similar fate to TD#2. 

 

Weaker TCs (TD to moderate TS) are more susceptible to dry air intrusion because WISHE heat exchange between the SSTs and the atmosphere hasn't really been fully established. We have a student that has been doing high resolution Hurricane-WRF Model simulations on weak TCs just after genesis. The results thus far show that even after genesis, there is still a 24-36 hour pulsing period where convection isn't always active, and cold downdrafts can interrupt the intensification process of the TC. In addition, the vertical PV tower that characterizes intense TCs has not been established, so dry air from outside of the inner core in the mid-levels can easily get into the circulation and intensify those cold downdrafts through entrainment. That's possibly what is happening today, and it's no accident this is happening during the diurnal minimum. 

[IsentropicLift]

The 18z GFS flipped back towards its previous idea of maintaining 93L, perhaps intensifying the system into a formidable TC in about two days as it approaches the islands. Thereafter uncertainty looms with relatively weak stirring currents as the system rides the southern periphery of the WAR. Assuming the system does develop, the Eastern Bahamas and Bermuda might see significant impacts. The 18z GFS restrengthens 93L into a Hurricane and eventually recurves OTS in about ten days. If the system sped up some or if the WAR retrogrades a bit more, the SE coast might come into play. Seems unlikely right now.

[Amped]

18z GFS D11 looks like a TS or CAT1 for Bermuda. Since the Euro shows nothing which usually means it has limited potential, and will be killed by shear long before day 11.

[phil882]

93L is really struggling against the SAL. It can sometimes be hard to quantify just how bad a SAL outbreak is and whether or not its actually impacting the system, but the Terra microwave imagery has some useful tools to help diagnosis the aerosol concentration in the environment. 

 

Look at the day to day changes from yesterday (when 93L was convectively active), to today (must less so).

 

July 28th, 2014

 

 

 

July 29th, 2014

 

 

The aerosol optical depth goes from 0.3-0.4 to the northeast of 93L yesterday to > 0.7 today. If you really want to squash convective activity, it's really about the concentration of aerosols that matters more than their actual presence. When the you start getting into large percentage concentrations, it can really modify the thermodynamic profile of the atmosphere. Think of the SAL as like an artificial capping inversion that is advected into the TC. Since the SAL absorbs some of the sun's radiation, it warms that portion of the atmosphere where the SAL is present. If this is substantial enough it could result in a cap that prevents convection from firing above that level (typically around 700 hPa). Deep convection in the tropics is not driven by very large CAPE amounts like the midwest, so it doesn't take much of an inversion to really squash deep convection.

 

At night though, without the sun's radiation, such an inversion should go away and convection might have a chance to refire. We'll see what happens tonight.

[Ground Scouring]

Anyone who's been regurgitating models over the past few days (as opposed to looking at the actual pitiful environment surrounding 93L) must be woozy at the change from hurricane to nada. And that nada, weak though it is, may still recurve. What a season. Oh, and I was right about the ECMWF being the better model and the system behind 93L going poof. Good record so far. The fact that a strong MJO failed to cause development is not a great sign for the season. Another bad sign is the low RH within (!) the ITCZ due to the complete and overpowering presence of the SAL. The below-average SSTA in the MDR certainly aren't going to help convection with 93L.

 

/End negative Nancy rant of the evenin'/

[wxtrackercody]

Anyone who's been regurgitating models over the past few days (as opposed to looking at the actual pitiful environment surrounding 93L) must be woozy at the change from hurricane to nada. And that nada, weak though it is, may still recurve. What a season. Oh, and I was right about the ECMWF being the better model and the system behind 93L going poof. Good record so far. The fact that a strong MJO failed to cause development is not a great sign for the season. Another bad sign is the low RH within (!) the ITCZ due to the complete and overpowering presence of the SAL. The below-average SSTA in the MDR certainly aren't going to help convection with 93L.

 

/End negative Nancy rant of the evenin'/

The MJO actually isn't in the Atlantic right now, it remains in the Pacific, hence the outbreak of tropical cyclones there. We should see it progress eastward, but it should also lose a lot of amplitude.

[IsentropicLift]

The MJO actually isn't in the Atlantic right now, it remains in the Pacific, hence the outbreak of tropical cyclones there. We should see it progress eastward, but it should also lose a lot of amplitude.

I believe a Kelvin wave just recently passed 93L.

[wxtrackercody]

I believe a Kelvin wave just recently passed 93L.

A strong one at that.

 

 

There is a difference between a convectively-coupled kelvin wave and the MJO, however.

[andyhb]

Anyone who's been regurgitating models over the past few days (as opposed to looking at the actual pitiful environment surrounding 93L) must be woozy at the change from hurricane to nada. And that nada, weak though it is, may still recurve. What a season. Oh, and I was right about the ECMWF being the better model and the system behind 93L going poof. Good record so far. The fact that a strong MJO failed to cause development is not a great sign for the season. Another bad sign is the low RH within (!) the ITCZ due to the complete and overpowering presence of the SAL. The below-average SSTA in the MDR certainly aren't going to help convection with 93L.

 

/End negative Nancy rant of the evenin'/

 

Please continue to pump your own tires over and over again even when no one was realistically expecting a hurricane out of this.

 

The fact that you have your user title as "Anti-weenie" is pretty silly considering you have made calls this year about the model verbatims without even looking at them (before 4/27-28 and also with Arthur). I'm not calling you a weenie by any means, but the people that are the complete opposite are often just as tedious.

[Srain]

As I mentioned on Monday, there is just too much dust across the MDR and convection has not remained concentrated or intact over the past couple of days regarding 93L. The easterly wave behind has also suffered the same fate.

It does appear further E across Africa that convective complexes/easterly waves are attempting to develop a bit further N between 10 and 12N as they move into Central Africa. The ITCZ continues to sag SE into the Gulf of Guinea and any potential tropical development would likely be a bit closer to the Western Caribbean Sea/Bay of Campeche or as we witnessed with Arthur, a MCV traveling across the Deep South along a stalled boundary as we enter the month of August.

[bluewave]

It's no surprise that we are seeing such a struggle with the dry air as the 500 mb RH

was the lowest on record over the MDR for July. 

 

[Kory]

Wow...failed to fire up some convection at DMAX.  I don't see a bright future for this system.  

 

If it stays fairly weak, it could very well ride the low level flow into the Caribbean. 

 

[phil882]

A really great illustration of how the dry air has been eating away at the convection of 93L. Just take a look at the TC size tool based on satellite imagery. 

 

 

The system went from an average sized disturbance to a system that's much smaller than average. Small systems can be very volatile in terms of intensity, and tend to not fare very well in high shear environments, similar to what 93L could be facing beyond 48 hours.