ATL: DANNY - Remnants - Discussion

[ROCK]

Relatively significant movement north?

more like gulping some dry air flattening out on the wet side...NHC said there would be ups and downs in intensity from here on out. Personally I dont think he has enough moisture envelope to protect it self. The globals are even catching on. When the CMC kills it and now the 12Z GFS.

[AtlanticWind]

Relatively significant movement north?

more like gulping some dry air flattening out on the wet side...NHC said there would be ups and downs in intensity from here on out. Personally I dont think he has enough moisture envelope to protect it self. The globals are even catching on. When the CMC kills it and now the 12Z GFS.

I would not go by this run .The Gfs and CMC did not initialize danny as a hurricane.

[tatertawt24]

Eye popping back out again?

[NCSTORMMAN]

Wow convection is decreasing again. Not sure what the cause is other than dry air but I thought that was to the north of Danny right now.

[Bocadude85]

[img][/img]

Eye popping back out again?

Yea it appears to be clearing out on visible.

http://www.ssd.noaa.gov/PS/TROP/floaters/04L/imagery/vis_lalo-animated.gif

[ozonepete]

I think the NHC means they're using TAFB and SAB estimates, both of which use an objective Dvorak technique. I don't know why TAFB and SAB come up with different numbers sometimes; probably slightly different input data, but one of the pro mets here probably knows. I'll look into it. Anyway, modified Dvorak techniques, such as CIMSS' ADT (Advanced Dvorak Technique) gets the original objective technique number and then runs additional algorithms to adjust the number for things the original technique doesn't always handle well. Your question is interesting, because while NHC's simpler method got 4.1 or 4.2, CIMSS' current ADT number is 3.1 which is clearly too low. But their analysis page shows they analyzed it without noting the eye so that's one reason they're way off. We will see how soon they catch it since they run every hour.

I was more reading it as the forecasters on shift did their own Dvorak classification, factoring in the eye scene. SAB was T3.0/45kt at 1145z, and TAFB was T3.5/55kt. Both too low.

With non-automated Dvorak, T-numbers come in either whole numbers or .5's, so probs not.

When they say subjective they mean that certain inputs, like the storm center location, are put in by the user, thus it's not objectively chosen by an algorithm. A completely objective technique would read everything from data files and pick the storm center and other inputs itself. CIMSS uses an algorithm that lets the software pick the center, among other subjective data, so they like to call it objective. In reality it is more objective but not completely objective because they have various inputs like their "weakening flag" which is not objective at all. That's why when you asked about "modified" I mentioned that CIMSS ADT is a modified Dvorak technique.

Anyway, with all of these changes and no one running exactly the same software, it's no wonder they all often come up with different numbers. I'm sure you've noticed that while NHC usually quotes TAFB/SAB numbers in its discussions, they do occasionally quote CIMSS numbers. I'm sure you've noticed that just like forecast models, one often outperforms the others at times but never for long. I'm also think it is quite possible that NHC has their own. I will ask them...

[ozonepete]

Btw, at 1615 UTC CIMSS still hasn't picked up the eye. That's one of the flaws in automated routines.

[ozonepete]

Hey Ozonepete. It is interesting and the NHC is ALWAYS careful to call out TAFB and SAB when they provided the T number. I interpreted this as the NHC did their own quick object scoring using an eye pattern (the eye had JUST popped up during the time the 11 AM package would have been written) whereas the other T numbers might have used non-eye pattern (since there wasn't a visible or IR eye at that time). Said differently, the eye popped out as the package was being written so the NHC ran its own classification (perhaps just by walking over to TAFB and having the analyst rework it using the eye pattern). I'll see what I can find out.

Hey long time no see. Hello!!
Haha I just posted about that. I think you are right. I'll wait for you to find out then and you can enlighten us all. Thanks!

[SouthFLTropics]

I wouldn't be so quick to write Danny off even if the dry air and shear impact Danny down the road and strip it of its convection. If it maintains that vigorous circulation, even as a naked swirl, we could possibly see it quickly flare back up if it finds the right conditions. I think with it being so small we are going to see crazy swings back and forth in intensity.

SFT

[ScottNAtlanta]

How many ACE points is Danny adding thus far? Does ACE take into account the size of the storm?

[RL3AO]

How many ACE points is Danny adding thus far? Does ACE take into account the size of the storm?

No, it only takes into account intensity and longevity. Danny is at 2.12

[Weatherboy1]

I wouldn't write Danny off down the road either, frankly. Shear may be an issue, as is dry air. But he certainly strengthened quickly this morning, and if he eventually avoids/dodges going over land areas like PR and/or Hispanola, he may yet surprise us down the road.

[tolakram]

Wow, I get busy and boom, Danny is a hurricane.

Early models showed a small storm and sure enough, Danny is unusually small.

live visible loop:

http://wwwghcc.msfc.nasa.gov/cgi-bin/get-goes?satellite=GOES-E%20HURRICANE&lat=13&lon=-40&info=vis&zoom=1&width=1024&height=768&type=Animation&quality=92&palette=ir1.pal&numframes=16&mapcolor=gray

[Hammy]

As far as the convection waning, it's not doing so nearly as quickly as it has the last few days, the deeper oranges (on RBTOP which I'm looking at) are maintaining, and there appears to be some extension of these colors close to the NW part of the eyewall as well. Likely short term fluctuations.

With a day or two left before unfavorable conditions arrive, what are the chances of this nearing the original forecast peak before weakening begins?

[BigB0882]

Reading through these threads can be funny if you haven't taken a peak in a couple of hours. You read at least 5 posts each of people claiming it is strengthening and people claiming it is weakening. Goes to show just how much these storms pulse up and down. These storms don't work on our timeframe, an hour to them is nothing. You need to see something happening for much longer than just a few frames of a satellite loop to be sure of anything.

Is there any way this hurricane can expand in size? Do tiny hurricanes ever grow into large hurricanes or even more average sized ones? The good news is even if it does get strong and makes landfall, hopefully the wind field will be tiny as well as storm surge area.

[Weatherboy1]

To elaborate further, Danny is NOT facing the "moving too fast/blowing itself apart" dilemma that killed off Debby in 2000. That was supposed to be a significant Florida threat but she moved too fast, tangled with Hispanola, and went "poof" in a day

http://www.nhc.noaa.gov/data/tracks/tracks-at-2000.png

The closest similar situation I remember may be Dean in 2001, who got sheared apart in the general vicinity of PR/Hispanola. But Danny has already fought off a lot more than Dean did, and formed a lot farther out in the Atlantic. So not really a great comparison.

http://www.nhc.noaa.gov/data/tracks/tracks-at-2001.png

Long story short, I think Danny could have a shot if he manages to avoid those islands.

[NCSTORMMAN]

Reading through these threads can be funny if you haven't taken a peak in a couple of hours. You read at least 5 posts each of people claiming it is strengthening and people claiming it is weakening. Goes to show just how much these storms pulse up and down. These storms don't work on our timeframe, an hour to them is nothing. You need to see something happening for much longer than just a few frames of a satellite loop to be sure of anything.

Is there any way this hurricane can expand in size? Do tiny hurricanes ever grow into large hurricanes or even more average sized ones? The good news is even if it does get strong and makes landfall, hopefully the wind field will be tiny as well as storm surge area.

They are valid questions from someone who doesn't know much about hurricanes and is seeking information. It is called gaining knowledge and this system has fluctuated quite often and more often than most storms because of its environment.

[ozonepete]

As far as the convection waning, it's not doing so nearly as quickly as it has the last few days, the deeper oranges (on RBTOP which I'm looking at) are maintaining, and there appears to be some extension of these colors close to the NW part of the eyewall as well. Likely short term fluctuations.

With a day or two left before unfavorable conditions arrive, what are the chances of this nearing the original forecast peak before weakening begins?

Small storms like this can bump up very rapidly. Since the dry air keeps running ahead of it and the shear will be light for another day or 2, it wouldn't surprise me if it made the original forecast winds. I believe it was for 100 mph, right?

[plazaglass]

How does Danny's current size compare to Charley in 2004? I seem to recall that was a small hurricane.

[Gustywind]

Danny Becomes First Atlantic Hurricane of 2015


http://www.wunderground.com/blog/JeffMa ... rynum=3079

The little storm that could, Danny, surged from weak tropical-storm status on Wednesday night to become the Atlantic’s first hurricane of the year on Thursday morning. At 11:00 am EDT Thursday, the top sustained winds in Hurricane Danny were estimated at 75 mph, or near minimal hurricane strength. Located in the remote central tropical Atlantic, near 12.5°N and 44.8°W, Danny remains far from land areas, roughly 1100 miles east of the Leeward Islands. Danny is moving west-northwest at about 12 mph, a fairly modest pace for tropical cyclones in this region.

Danny was largely stripped of its core convection (showers and thunderstorms) on Wednesday, as dry air filtered into its center, but the storm retained its overall structure and was able to rebuild central convection on Wednesday night, even managing to produce an eyewall formation and a visible eye over the last few hours. Danny’s quick intensification was facilitated by its small size (see Figure 3 below). Hurricane-force winds only spanned a region 20 miles in diameter on Thursday morning, with tropical-storm-force winds extending out up to 60 miles from the center. Smaller tropical cyclones are able to both intensify and weaken more rapidly, which makes intensity prediction especially challenging. That said, Danny’s rise to hurricane status was well forecast several days in advance by the recently upgraded HWRF model, and since Tuesday by the GFDL model. The leading statistics-based models, which are the most accurate guidance for intensity beyond about three days, also gave a solid heads-up that Danny could attain hurricane status by today.



The outlook for Danny
Despite the overnight growth spurt, Danny’s future as a hurricane remains highly uncertain. One of the two main obstacles it faces is a huge zone of relatively dry, dusty air that extends across most of the Atlantic around 20°N latitude (see Figure 4). Any large-scale intrusion of this air into Danny’s circulation would tamp down the instability that fuels convection. Thus far, Danny has been able to generate and consolidate enough shower and thunderstorm activity to fight off injections of dry air--another benefit of its small size. As it slowly gains latitude, Danny will be at increasing risk of falling victim to this zone of dry air, provided it does not shift to the northeast in tandem with Danny’s northwestward motion.
Danny’s other nemesis is vertical wind shear, a perennial feature in the North Atlantic tropics during El Niño years. The widespread rising of warm air over the eastern tropical Pacific during El Niño helps foster unusually strong west winds at upper levels, pushing away from the Niño region into the Caribbean and western Atlantic. Such shear can easily disrupt the chimney-like vertical structure that helps to maintain a tropical cyclone’s strength. Currently, wind shear over the Caribbean is below the record values observed earlier this summer, but values of 30 - 60 mph remain widespread. (Anything above 20 knots, or about 23 mph, is problematic for tropical cyclone development.) For now, shear over Danny remains low, in part because its potent convection has produced a small zone of high pressure overhead. This weekend, Danny will be hard-pressed to avoid encountering a belt of higher shear, which would not only jeopardize its structure but also help push dry, dusty air into its circulation. If Danny survives that passage as a well-structured tropical cyclone, then it may encounter somewhat lower shear values ahead of its path early next week (see Figure 5), as a weak but persistent upper-level low is predicted to move northward from the Bahamas and a ridge builds in to replace it.