ATL: DORIAN - Post-Tropical - Discussion

[BYG Jacob]

A named storm in the MDR? UNPOSSIBLE

[DioBrando]

DISCUSSION OUT, LADS:

Visible and passive microwave satellite imagery indicate that the
inner-core of the small cyclone has noticeably improved since the
previous advisory. A 1705Z AMSR-2 overpass showed the development
of tightly curved bands and a 10 mile wide eye-like feature. In
addition, a 1935Z SSMI/S microwave pass revealed a tightly curved
band in 91 GHz data that wrapped almost 75 percent around the
center. Based on the much improved inner-core structure and 33-kt
wind vectors in an earlier ASCAT-B pass, the depression has been
upgraded to Tropical Storm Dorian on this advisory. Upper-level
outflow has been improving to the northwest, but remains slightly
restricted to the southeast due to some modest southeasterly
vertical wind shear.

The initial motion is 280/11 kt. The latest NHC model guidance
remains in excellent agreement that Dorian will generally move
west-northwestward for the next 5 days around the southern periphery
of the sprawling Bermuda-Azores high pressure ridge that is located
to the north of the Lesser and Greater Antilles. This motion is
expected to bring Dorian through the central or northern Lesser
Antilles on Tuesday, possibly as a hurricane, and then into the
northeastern Caribbean Sea on Wednesday and Thursday. The official
forecast track was shifted slightly north of the previous advisory
track, and is close to the consensus model TVCN, which remains north
of the NOAA HCCA corrected-consensus model.

The moderate to strong vertical wind shear that has been hindering
development of this system for the past several days is forecast to
diminish significantly during the next 12 h, and remain near 5 kt
through Tuesday. The low shear conditions, along with warm SSTs and
the significantly improved small, inner-core structure, should allow
for at least slow but steady strengthening despite the abundance of
dry mid-level air nearby. However, the low vertical wind shear and
tight inner-core wind field are also harbingers of possible rapid
intensification. For now, the new intensity forecast remains
conservative and similar to the previous advisory, and is above all
of the available intensity guidance, including the HWRF model.

Key Messages:
1. Dorian is forecast to strengthen and could be near hurricane
strength when it approaches the Lesser Antilles on Tuesday.

2. It is too soon to determine the specific timing or magnitude of
impacts in the Lesser Antilles, but tropical storm or hurricane
watches may be needed for a portion of the area on Sunday.


FORECAST POSITIONS AND MAX WINDS

INIT 24/2100Z 10.7N 49.1W 35 KT 40 MPH
12H 25/0600Z 11.0N 50.7W 40 KT 45 MPH
24H 25/1800Z 11.4N 52.8W 45 KT 50 MPH
36H 26/0600Z 11.9N 54.9W 50 KT 60 MPH
48H 26/1800Z 12.7N 57.0W 55 KT 65 MPH
72H 27/1800Z 14.6N 61.1W 65 KT 75 MPH
96H 28/1800Z 16.5N 65.3W 75 KT 85 MPH
120H 29/1800Z 18.4N 69.0W 70 KT 80 MPH...INLAND

$$
Forecaster Stewart

[1900hurricane]

Interesting that the NHC mentions the rapid intensification possibilities. I looked at the SHIPS output, and sure enough, there are some decent probs in the RI matrix. Chances are at least double climatology, and even more in the 48-72 tau period.

* ATLANTIC 2019 SHIPS INTENSITY FORECAST *
* IR SAT DATA AVAILABLE, OHC AVAILABLE *
* FIVE AL052019 08/24/19 18 UTC *

TIME (HR) 0 6 12 18 24 36 48 60 72 84 96 108 120
V (KT) NO LAND 30 32 34 36 39 44 52 59 66 67 71 70 69
V (KT) LAND 30 32 34 36 39 44 52 59 66 67 71 70 69
V (KT) LGEM 30 32 34 36 38 43 48 53 58 61 63 64 62
Storm Type TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP TROP

SHEAR (KT) 13 7 3 5 5 9 10 10 10 13 6 16 16
SHEAR ADJ (KT) -2 1 3 2 1 1 -1 -3 -2 -6 0 -1 -3
SHEAR DIR 122 135 98 24 18 336 348 288 284 250 233 236 261
SST (C) 27.9 28.0 28.0 28.0 28.2 28.4 28.8 29.0 29.2 29.4 29.3 29.2 29.1
POT. INT. (KT) 136 137 137 137 140 142 149 152 155 158 156 155 154
ADJ. POT. INT. 135 136 136 136 139 142 147 150 152 155 151 150 147
200 MB T (C) -53.8 -53.8 -54.0 -54.1 -54.0 -54.3 -53.9 -54.0 -53.9 -54.1 -54.3 -54.5 -54.3
200 MB VXT (C) -0.1 -0.2 -0.2 -0.2 -0.2 -0.1 -0.2 -0.2 -0.2 -0.2 -0.2 -0.2 -0.2
TH_E DEV (C) 9 9 9 9 10 10 10 10 11 11 11 11 11
700-500 MB RH 43 44 41 39 40 42 46 48 50 49 51 50 54
MODEL VTX (KT) 13 13 12 11 11 11 11 10 10 7 8 6 4
850 MB ENV VOR 41 36 26 19 21 0 17 13 18 15 25 12 5
200 MB DIV 2 -6 -11 -22 -19 -4 -4 19 22 31 43 1 9
700-850 TADV -6 -6 -6 -8 -7 -4 0 0 0 0 2 0 0
LAND (KM) 760 715 682 655 641 617 515 389 358 456 313 144 81
LAT (DEG N) 10.6 10.8 10.9 11.1 11.3 11.7 12.5 13.3 14.0 14.8 15.7 16.7 17.7
LONG(DEG W) 48.6 49.6 50.6 51.6 52.6 54.8 56.6 58.5 60.6 62.4 64.2 65.9 67.9
STM SPEED (KT) 11 10 10 10 10 10 10 11 10 10 9 10 11
HEAT CONTENT 11 12 12 12 14 26 40 41 38 49 47 65 84

FORECAST TRACK FROM OFCI INITIAL HEADING/SPEED (DEG/KT):280/ 11 CX,CY: -10/ 2
T-12 MAX WIND: 25 PRESSURE OF STEERING LEVEL (MB): 534 (MEAN=620)
GOES IR BRIGHTNESS TEMP. STD DEV. 50-200 KM RAD: 20.2 (MEAN=14.5)
% GOES IR PIXELS WITH T < -20 C 50-200 KM RAD: 45.0 (MEAN=65.0)
PRELIM RI PROB (DV .GE. 35 KT IN 36 HR): 6.3

INDIVIDUAL CONTRIBUTIONS TO INTENSITY CHANGE
6 12 18 24 36 48 60 72 84 96 108 120
----------------------------------------------------------
SAMPLE MEAN CHANGE 1. 2. 3. 4. 6. 8. 9. 10. 11. 11. 12. 12.
SST POTENTIAL 0. 0. 1. 1. 3. 8. 15. 20. 25. 28. 31. 33.
VERTICAL SHEAR MAG 1. 2. 3. 4. 6. 8. 9. 9. 9. 9. 8. 7.
VERTICAL SHEAR ADJ 0. 0. 0. 0. 0. 0. 1. 2. 3. 2. 2. 2.
VERTICAL SHEAR DIR 0. 0. 1. 1. 2. 3. 3. 2. 1. -1. -2. -4.
PERSISTENCE 1. 1. 1. 1. 1. 0. 0. 0. 0. 0. 0. 0.
200/250 MB TEMP. 0. 0. -1. -1. 0. 0. 0. 0. 0. 1. 1. 1.
THETA_E EXCESS 0. 0. 0. 0. 1. 1. 1. 1. 1. 1. 1. 1.
700-500 MB RH 0. 0. 1. 1. 1. 2. 3. 3. 3. 2. 2. 2.
MODEL VTX TENDENCY 0. -1. -1. -2. -3. -3. -6. -7. -11. -12. -15. -18.
850 MB ENV VORTICITY 0. 0. 0. 0. 0. 0. 0. 0. -1. -1. -1. -1.
200 MB DIVERGENCE 0. 0. -1. -1. -1. -1. -1. -1. -1. 0. 0. 1.
850-700 T ADVEC 0. 0. 0. 0. -1. -1. -1. -1. -1. -1. 0. 0.
ZONAL STORM MOTION 0. 0. 0. 0. 0. 1. 1. 1. 1. 2. 2. 2.
STEERING LEVEL PRES 0. 0. 0. 0. 1. 1. 0. 1. 1. 1. 1. 1.
DAYS FROM CLIM. PEAK 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0.
GOES PREDICTORS 0. 0. 0. -1. -1. -1. -2. -2. -3. -3. -3. -3.
OCEAN HEAT CONTENT 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0.
RI POTENTIAL 0. 0. -1. -1. -2. -2. -1. -1. 0. 0. 1. 1.
----------------------------------------------------------
TOTAL CHANGE 2. 4. 6. 9. 14. 22. 29. 36. 37. 41. 40. 39.

CURRENT MAX WIND (KT): 30. LAT, LON: 10.6 48.6

** 2019 ATLANTIC RI INDEX AL052019 FIVE 08/24/19 18 UTC **
(SHIPS-RII PREDICTOR TABLE for 30 KT OR MORE MAXIMUM WIND INCREASE IN NEXT 24-h)

Predictor Value RI Predictor Range Scaled Value(0-1) % Contribution
12 HR PERSISTENCE (KT) : 5.0 -49.5 to 33.0 0.66 5.9
850-200 MB SHEAR (KT) : 6.7 30.1 to 2.3 0.84 2.9
HEAT CONTENT (KJ/CM2) : 12.2 0.0 to 151.8 0.08 0.2
STD DEV OF IR BR TEMP : 20.2 36.6 to 2.8 0.49 1.8
MAXIMUM WIND (KT) : 30.0 22.5 to 137.5 0.20 0.4
2nd PC OF IR BR TEMP : -0.9 2.9 to -2.9 0.66 1.6
POT = MPI-VMAX (KT) : 106.4 27.5 to 139.6 0.70 1.7
D200 (10**7s-1) : -11.2 -29.7 to 185.9 0.09 0.1
%area of TPW <45 mm upshear : 15.6 100.0 to 0.0 0.84 0.0
BL DRY-AIR FLUX (W/M2) : 264.6 895.4 to -55.0 0.66 0.0

SHIPS Prob RI for 20kt/ 12hr RI threshold= 6% is 1.1 times climatological mean ( 5.2%)
SHIPS Prob RI for 25kt/ 24hr RI threshold= 21% is 1.9 times climatological mean (10.9%)
SHIPS Prob RI for 30kt/ 24hr RI threshold= 15% is 2.1 times climatological mean ( 6.9%)
SHIPS Prob RI for 35kt/ 24hr RI threshold= 10% is 2.5 times climatological mean ( 3.8%)
SHIPS Prob RI for 40kt/ 24hr RI threshold= 10% is 4.0 times climatological mean ( 2.4%)
SHIPS Prob RI for 45kt/ 36hr RI threshold= 12% is 2.6 times climatological mean ( 4.5%)
SHIPS Prob RI for 55kt/ 48hr RI threshold= 16% is 3.4 times climatological mean ( 4.6%)
SHIPS Prob RI for 65kt/ 72hr RI threshold= 33% is 6.2 times climatological mean ( 5.4%)

Matrix of RI probabilities
------------------------------------------------------------------------------
RI (kt / h) | 20/12 | 25/24 | 30/24 | 35/24 | 40/24 | 45/36 | 55/48 |65/72
------------------------------------------------------------------------------
SHIPS-RII: 5.9% 20.9% 14.6% 9.6% 9.5% 11.5% 15.7% 33.4%
Logistic: 4.8% 20.1% 16.5% 5.3% 1.9% 10.3% 13.1% 20.1%
Bayesian: 0.6% 4.1% 2.4% 0.0% 0.0% 0.6% 1.1% 0.7%
Consensus: 3.8% 15.0% 11.2% 5.0% 3.8% 7.5% 10.0% 18.1%
DTOPS: 0.0% 1.0% 0.0% 0.0% 0.0% 0.0% 3.0% 4.0%

## ANNULAR HURRICANE INDEX (AHI) AL052019 FIVE 08/24/19 18 UTC ##
## STORM NOT ANNULAR, SCREENING STEP FAILED, NPASS=4 NFAIL=3 ##
## AHI= 0 (AHI OF 100 IS BEST FIT TO ANN. STRUC., 1 IS MARGINAL, 0 IS NOT ANNULAR) ##

** PROBLTY OF AT LEAST 1 SCNDRY EYEWL FORMTN EVENT AL052019 FIVE 08/24/2019 18 UTC **
TIME(HR) 0-12 12-24(0-24) 24-36(0-36) 36-48(0-48)
CLIMO(%) 0 0( 0) 0( 0) 0( 0) <-- PROB BASED ON INTENSITY ONLY
PROB(%) 0 0( 0) 0( 0) 0( 0) <-- FULL MODEL PROB (RAN NORMALLY)

** DSHIPS INTENSITY FORECAST ADJUSTED RELATIVE TO ONSET OF ERC WEAKENING PHASE **
TIME (HR) 0 6 12 18 24 36 48 60 72 84 96 108 120
>24HR AGO (DSHIPS) 30 32 34 36 39 44 52 59 66 67 71 70 69
18HR AGO 30 29 31 33 36 41 49 56 63 64 68 67 66
12HR AGO 30 27 26 28 31 36 44 51 58 59 63 62 61
6HR AGO 30 24 21 20 23 28 36 43 50 51 55 54 53
NOW CURRENT INTENSITY < 83 KT
IN 6HR INTENSITY IN 6HR < 83 KT
IN 12HR INTENSITY IN 12HR < 83 KT

[zhukm29]

It appears that the NHC is claiming that their intensity forecast is conservative... that's certainly alarming. The NHC is known for underdoing the intensity forecasts, so the fact that this forecast is considered conservative is not good news. They do have more resources than we do, so this is a bit worrying.

[PTrackerLA]

It appears that the NHC is claiming that their intensity forecast is conservative... that's certainly alarming. The NHC is known for underdoing the intensity forecasts, so the fact that this forecast is considered conservative is not good news. They do have more resources than we do, so this is a bit worrying.

That part didn't male any sense to me, their intensity forecast is conservative yet above ALL model guidance?

[Kazmit]

It appears that the NHC is claiming that their intensity forecast is conservative... that's certainly alarming. The NHC is known for underdoing the intensity forecasts, so the fact that this forecast is considered conservative is not good news. They do have more resources than we do, so this is a bit worrying.

That part didn't male any sense to me, their intensity forecast is conservative yet above ALL model guidance?

I suppose they don't have to base their forecast off of what the models show.

[DioBrando]

 https://twitter.com/CC_StormWatch/status/1165367509337481217

[AxaltaRacing24]

if this storm goes north of the shredder, things might get very interesting.

[Hypercane_Kyle]

It appears that the NHC is claiming that their intensity forecast is conservative... that's certainly alarming. The NHC is known for underdoing the intensity forecasts, so the fact that this forecast is considered conservative is not good news. They do have more resources than we do, so this is a bit worrying.

That part didn't male any sense to me, their intensity forecast is conservative yet above ALL model guidance?

I'm betting the NHC thinks the global models have a poor handle on the system, which makes sense considering the ECMWF hardly even showed a vortex, let alone a TC, until like yesterday for Dorian.

[zal0phus]

I'm anticipating something like 2015 Danny, Dorian doesn't have the devastating hurricane vibe to me but you never know
The possibility of intensification that was mentioned is alarming. I wonder where this will end up.

[1900hurricane]

This is the core structure NHC is mentioning. It looks much better than the IR presentation, and even includes the cyan ring on 37 GHz.

[zhukm29]

It appears that the NHC is claiming that their intensity forecast is conservative... that's certainly alarming. The NHC is known for underdoing the intensity forecasts, so the fact that this forecast is considered conservative is not good news. They do have more resources than we do, so this is a bit worrying.

That part didn't male any sense to me, their intensity forecast is conservative yet above ALL model guidance?

The thing is that models are only one factor that the NHC uses to determine the track, and we all know that intensity is the factor that models are most wrong about. I believe that the NHC is saying that even though the intensity models are not bullish, the environmental conditions that Dorian will be in for the next few days will be perfect for rapid intensification. Intensity models are very bad at predicting RI.

This is a situation where evidence on the environmental conditions is used to justify something happening that may not be picked up by the models. Forecasters at the NHC don't use models as the only source to follow when building a forecast; they use much more data that they have on hand, and it appears that this data is pointing to a stronger intensity than the models are predicting.

[AtlanticWind]

I think the small size of the system in a very low shear and high SST is always a threat for RI.

Models can be behind the curve on these situations.

Remember a few days ago I don't think anyone was expecting an intesfying system in the MDR this weekend.

[zhukm29]

 https://twitter.com/WxTca/status/1165369797162479617

[BYG Jacob]

This is the core structure NHC is mentioning. It looks much better than the IR presentation, and even includes the cyan ring on 37 GHz.

https://i.imgur.com/YIgaU0y.jpg

https://i.imgur.com/JCbZmi9.jpg

Looks damn close to hurricane status, like Beryl last year.

[Hypercane_Kyle]

I also think the NHC is calling the intensity forecast "conservative" through the next 48 hours. Dorian's a tiny system that looks primed to pull a fast one and become a hurricane in the MDR, much like Beryl last year.

[zhukm29]

 https://twitter.com/pppapin/status/1165371107014103040

[Hammy]

I also think the NHC is calling the intensity forecast "conservative" through the next 48 hours. Dorian's a tiny system that looks primed to pull a fast one and become a hurricane in the MDR, much like Beryl last year.

I think another factor is that due to the small size, the models are not able to initialize it as well--Danny in 2015 and Beryl last year were good examples of this.

[Nimbus]

Convective burst over the LLC at sunset, so its made it through the dry air.

[Weatherwatcher2018]

Should I cancel monday night dinner plans in Barbados or too early