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WxWatcher007

Category Five Hurricane Dorian

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TD 5 has formed and is expected to become a hurricane. First NHC discussion and track below.

Tropical Depression Five Discussion Number   1
NWS National Hurricane Center Miami FL       AL052019
1100 AM AST Sat Aug 24 2019

The small low pressure system that the NHC has been tracking the
past several days across the tropical Atlantic Ocean has acquired
enough deep convection to be classified as a tropical depression,
the fifth tropical cyclone of the 2019 hurricane season. Two ASCAT
passes between 1200-1300Z this morning indicated that the system
had a closed circulation and surface winds of at least 30 kt, and
that is the intensity set for this advisory. Upper-level outflow
is fair to the northwest and restricted to the southeast due to
moderate easterly vertical wind shear.

The initial motion estimate is 280/10 kt. The NHC model guidance is
in very good agreement that the cyclone will move in a general
west-northwestward direction along the southern periphery of a
deep-layer ridge for the next 5 days, bring the system through the
central or northern Lesser Antilles on Tuesday, and into the
northeastern Caribbean Sea on Wednesday and Thursday. The official
forecast track is close to the consensus model TVCN, which is a
little north of the NOAA HCCA corrected-consensus model.

The small cyclone is currently experiencing easterly to
southeasterly shear of about 15 kt. The shear is forecast to
steadily decrease over the next 24 h and be around 5 kt in the
24-to-72-hour time period. Although the depression is expected to
remain embedded in a fairly dry mid-level environment, the small
overall circulation, small radius of maximum winds, low shear
regime, and warm SSTs of 28.0-28.5 deg C should allow for slow but
steady intensification through the 5-day period despite occasional
intrusions of dry air. The NHC intensity forecast is a blend of the
statistical-dynamical SHIPS and LGEM models, and the more robust
HWRF model.

FORECAST POSITIONS AND MAX WINDS

INIT  24/1500Z 10.4N  47.9W   30 KT  35 MPH
 12H  25/0000Z 10.7N  49.4W   30 KT  35 MPH
 24H  25/1200Z 11.0N  51.4W   35 KT  40 MPH
 36H  26/0000Z 11.4N  53.5W   40 KT  45 MPH
 48H  26/1200Z 12.0N  55.5W   45 KT  50 MPH
 72H  27/1200Z 13.6N  59.3W   55 KT  65 MPH
 96H  28/1200Z 15.2N  63.1W   65 KT  75 MPH
120H  29/1200Z 17.1N  66.7W   75 KT  85 MPH

$$
Forecaster Stewart

99WCHJ6.png

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Seeing it that close to Puerto Rico is not a scenario anyone should want.

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The past couple of discussions about the wave seemed to indicate that longer term winds/dry air would be unfavorable for development once it passed the Antilles.  Now reading the first discussion on TD5 they say slow steady strengthening even with intrusions of dry air and have it at hurricane strength as it nears the Puerto Rico area.

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2 hours ago, wxeyeNH said:

The past couple of discussions about the wave seemed to indicate that longer term winds/dry air would be unfavorable for development once it passed the Antilles.  Now reading the first discussion on TD5 they say slow steady strengthening even with intrusions of dry air and have it at hurricane strength as it nears the Puerto Rico area.

Look at the forecaster on duty. I knew who it would be the moment I saw it tweeted about this morning. 

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2 minutes ago, WxWatcher007 said:

Pretty nice win for the GFS.

Incredible stuff. The Euro and GFS before the upgrade have always struggled with these mesoscale features. Partly I feel is due to poor soundings and initialization data in this sparse region.

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8 minutes ago, Windspeed said:

 

Was wondering how a short term burst in intensity or RI wouldt effect track. The consensus models are all weak so how would they react to a stronger system. Further north?

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Dorian has a small area of concentrated convection around a small vortex. It already has curved banding near the center, even if the cloudtops aren't all that impressive yet. There is just enough convective bursting and cells to keep assisting the vortex however with it being so small. Keep in mind, that is delicate and easterlies could interfere pretty easily with such a small system. But the easterlies are forecast to continue relaxing. Therefore if the small vortex has a persistent MCS develop over the core, we might get to see a rarer microcane form prior to interaction with the Lesser Antilles. Of course with time the system would grow larger and evolve out of microcane size to something more typical, especially after an ERC or two. Dry air could also play factor in keeping the system compact in the short-to-midterm. With relaxing easterly shear and a decent upper ridge for the next 3 days, dry air intrusion is the only limiting factor. But it is a big factor.

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Was wondering how a short term burst in intensity or RI wouldt effect track. The consensus models are all weak so how would they react to a stronger system. Further north?

500 mb ridging will remain strong enough to get Dorian into the eastern Caribbean and Antilles on a WNW heading regardless of TC intensity. Afterwards, western Atlantic ridging may be weaker allowing for a more NW to northern track. But Dorian may encounter Hispaniola as well. It's really too early to know or even guess how that will play out. That breakdown is also enough days out in modeling that it may not even occur.

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13 minutes ago, Windspeed said:
35 minutes ago, shaggy said:
Was wondering how a short term burst in intensity or RI wouldt effect track. The consensus models are all weak so how would they react to a stronger system. Further north?

 

500 mb ridging will remain strong enough to get Dorian into the eastern Caribbean and Antilles on a WNW heading regardless of TC intensity. Afterwards, western Atlantic ridging may be weaker allowing for a more NW to northern track. But Dorian may encounter Hispaniola as well. It's really too early to know or even guess how that will play out. That breakdown is also enough days out in modeling that it may not even occur.

I was just looking at forecast track and thinking even a 50-100 mile shift to the north would remove shreddinola from a direct center crossing. PR looks to have issues no matter what but a miss of the bigger peaks would certainly allow it to hold intensity.......unless of course the mom models are right and theres not.much of a storm left when it gets there.

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I was just looking at forecast track and thinking even a 50-100 mile shift to the north would remove shreddinola from a direct center crossing. PR looks to have issues no matter what but a miss of the bigger peaks would certainly allow it to hold intensity.......unless of course the mom models are right and theres not.much of a storm left when it gets there.

The most interesting feature to me isn't so much mid level ridging completely breaking down. That will still be in place to keep the wnw heading. However, after three days, a 400-300 mb level upper low/trough or TUTT north of the Antilles is being modeled. Positioning of Dorian when that forms is most critical as a strong shear axis will either impede Dorian negatively or create strong ventilation to the north based on proximity. Though difficult to forecast that precisely looking this far in advance.
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Even though convection is still sparsely distributed, the recent microwave scan posted above by Papin was very revealing. Following that scan, even looking at a simple AVN IR image, you can clearly make out the compact vortex with a ring of cooler cloudtops with several strong cells. Sure, just focusing on the spread of cold cloudtops / deep convection doesn't tell the complete tale. You could say this still looks like crap. But it is still near the organizing / formative stages. Already having a symmetrical structure will be important if deeper convection can and does take off in the next 12 hours. This could ramp up intensity rather quickly.9c36f88a7125a658572f971f7a9b91ed.gif

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2 hours ago, Windspeed said:

Even though convection is still sparsely distributed, the recent microwave scan posted above by Papin was very revealing. Following that scan, even looking at a simple AVN IR image, you can clearly make out the compact vortex with a ring of cooler cloudtops with several strong cells. Sure, just focusing on the spread of cold cloudtops / deep convection doesn't tell the complete tale. You could say this still looks like crap. But it is still near the organizing / formative stages. Already having a symmetrical structure will be important if deeper convection can and does take off in the next 12 hours. This could ramp up intensity rather quickly.9c36f88a7125a658572f971f7a9b91ed.gif

 

1 hour ago, Windspeed said:

 

Been working all day so I haven't had a chance to really dive in until now. As always, you and Levi cover it very well.

I perked up big time looking at the microwave images posted earlier this evening. That's certainly a compelling signal for RI, and it looks like there's a little burst of convection over the center. Have you seen the SHIPS guidance? Definitely something to watch in the next 48 hours as dry air entrainment looks to be the only major inhibitor of intensification.

This long range forecast is wide open, and I hope no one here gets too hung up in the variation we see in the guidance. Just 24 hours before development not a single EPS member had forecasted development. Incredible.

Hopefully, this misses Puerto Rico...

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Chips are stacked against Dorian at this point. Between the death zone, Hispaniola and the TUTT its gonna be hard for this to thread the needle. Seems like the shear has kept up longer than thought yesterday and then only real chance I thought it had was to deepen quickly and miss Hispaniola to the east.

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Chips are stacked against Dorian at this point. Between the death zone, Hispaniola and the TUTT its gonna be hard for this to thread the needle. Seems like the shear has kept up longer than thought yesterday and then only real chance I thought it had was to deepen quickly and miss Hispaniola to the east.

Being a small system, it probably does have a rough go in a few days. However, in the short term, it still has a good deal of ocean to cross and improving favorability for intensification prior to reaching the islands. Again, it only takes this pulsing convection to deepen the vortex and low enough and it will begin increasing its own surface convergence. It looks like there is a nice mcs and cdo perhaps starting for form right over the vortex during the past several hours.

e5c98d4e6ec53f33a76349167f28cdc5.gif

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Tropical Storm Dorian Discussion Number   5
NWS National Hurricane Center Miami FL       AL052019
1100 AM AST Sun Aug 25 2019

The convective organization of Dorian has improved a little since
the last advisory, as a more persistent area of central convection
has formed along with increased, but ragged, outer banding.
However, the various satellite intensity estimates remain clustered
around 35 kt, and that remains the initial intensity.

A combination of 1-minute GOES-16 visible imagery and microwave
satellite data have helped pinpoint the center, and the initial
motion is 280/12.  The subtropical ridge to the north of the
cyclone should steer it generally westward to west-northwestward
for the next 3-4 days, with a more northwestward motion possible
thereafter as Dorian approaches an upper-level low pressure area
forecast to be over the north-central Caribbean.  The model
guidance continues the previous trend of being south of and a bit
faster than the previous runs, and as a result the new forecast
track is again shifted a little to the south.  The new forecast
lies between the previous forecast and the various consensus
models.  However, it is south of the forecasts of the HWRF, the
UKMET, and the UKMET Ensemble mean.  Additional adjustments to the
track may be required on the next advisory if the current model
trends continue.

While vertical wind shear is decreasing over Dorian, the cyclone
still appears to be ingesting dry air based on the ragged convective
pattern.  Some dry air entrainment is expected to continue for the
next few days, and based on this the new intensity forecast again
calls for gradual strengthening through 72 h.  This part of the
intensity forecast is in best agreement with the SHIPS model, and it
lies near the upper edge of the intensity guidance.  The intensity
forecast becomes low confidence after 72 h due to uncertainties in
the amount of shear and land that Dorian will encounter.  The new
forecast calls for some weakening due to shear before Dorian moves
over Hispaniola, followed by weakening to a depression due to
passage over the island.  However, the large range of possibilities
includes both Dorian going north of Hispaniola and remaining a
hurricane and the small cyclone dissipating completely over
Hispaniola.

Key Messages:

1. A Tropical Storm Warning has been issued for Barbados, and a
Tropical Storm Watch is in effect for St. Lucia, St. Vincent, and
the Grenadines. Additional watches and warnings for other portions
of the Lesser Antilles could be required later today.

2. It is too soon to determine the specific timing or magnitude of
impacts in Puerto Rico, the Virgin Islands, or Hispaniola, but
interests in those areas should monitor the progress of Dorian.

FORECAST POSITIONS AND MAX WINDS

INIT  25/1500Z 11.2N  52.9W   35 KT  40 MPH
 12H  26/0000Z 11.5N  54.6W   40 KT  45 MPH
 24H  26/1200Z 12.0N  56.9W   45 KT  50 MPH
 36H  27/0000Z 12.7N  59.1W   50 KT  60 MPH
 48H  27/1200Z 13.5N  61.2W   55 KT  65 MPH
 72H  28/1200Z 15.6N  65.3W   65 KT  75 MPH
 96H  29/1200Z 17.5N  69.0W   60 KT  70 MPH
120H  30/1200Z 20.0N  72.0W   25 KT  30 MPH

$$
Forecaster Beven
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Best burst of convection yet for Dorian.

However, the longevity of the convection has been an issue. We'll see if things stick this time.

(couldn't load gif lol) 

rEWqyeY.jpg

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Continuing to improve. Deep convection and hot towers with rapid lighting detection in the past hour right over the center. Vortex should take off now with pressure drop. Core formation should be underway.ded78b04a00f80cf9767f006da2727a3.gif

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It looks like the internal structure has improved a bit.

Still not entirely closed off yet, but intensification is occurring nonetheless. First low level recon scheduled for tomorrow.

YX9L1NV.jpg

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Not sure why NHC has peak intensity in 72hrs.  Based on shear, it looks like Dorian will rapidly strengthen in the next 24hrs, then start to weaken kind of like Beryl last year.  

 

Edit: There is some very dry air to the west of the storm possibly inhibiting it in the short range. Maybe why the statistical models show deepening after 48hrs in increasing shear.

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This is a fantastic illustration of Dorian’s progress during the day. Convection hasn’t been an issue today. Nice and gradual bout of organization and intensification.

 

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