ATL: GASTON - Post-Tropical - Discussion

[Ntxw]

RGB loop. This is a great storm for cyclone enthusiasts of the Atlantic to track. Very reminiscent of the Pacific systems and (Joaquin aside arguably) could be the best system in years in this basin IMO.

[cycloneye]

No Hurricane yet?

18z Best track:

Location: 13.9°N 35.1°W
Maximum Winds: 55 kt Gusts: N/A
Minimum Central Pressure: 1002 mb
Environmental Pressure: 1013 mb
Radius of Circulation: 270 NM
Radius of Maximum Wind: 20 NM
Eye Diameter: N/A

[Nimbus]

Smal eye will help it with the dry air, will need a couple eyewall replacement cycles before it gets "picturesque". May be too dry to get that classic pentagram formation in the eye.

[cycloneye]

TROPICAL STORM GASTON DISCUSSION NUMBER 5
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
500 PM AST TUE AUG 23 2016

The cloud pattern of Gaston has not changed much during the past
several hours, although perhaps the convection has become more
symmetric. Satellite classifications are about the same as before,
so the initial wind speed remains 55 kt. Gaston has about 24-36
hours to intensify before southwesterly vertical wind shear
associated with a mid-tropospheric trough is forecast to increase.
This shear should result in some weakening of the cyclone in the
2 or 3 day time frame. Thereafter, Gaston moves away from the
trough, and since the cyclone should be over warm waters near 29C,
some restrengthing is likely. Considering the complexity of the
scenario, the guidance is in relatively good agreement on this
pattern. The official forecast follows the trend of the previous
forecast and the intensity consensus.

The initial motion estimate is 290/16. Gaston should gradually turn
northwestward during the next couple of days as it moves around the
subtropical ridge. Guidance is in very good agreement on the
forecast during that time, and little change is made to the
previous NHC track in the shorter term. Beyond 3 days, a break in
the subtropical ridge is forecast, although the models are not in
great agreement on exactly what longitude Gaston reaches before its
likely recurvature. Overall, the model guidance has shifted a bit
westward, and the latest NHC track forecast is shifted in that
direction.

FORECAST POSITIONS AND MAX WINDS

INIT 23/2100Z 14.2N 35.8W 55 KT 65 MPH
12H 24/0600Z 15.2N 38.1W 65 KT 75 MPH
24H 24/1800Z 16.8N 40.7W 75 KT 85 MPH
36H 25/0600Z 18.7N 43.2W 80 KT 90 MPH
48H 25/1800Z 20.8N 45.4W 80 KT 90 MPH
72H 26/1800Z 25.5N 49.6W 70 KT 80 MPH
96H 27/1800Z 28.5N 53.5W 75 KT 85 MPH
120H 28/1800Z 31.0N 54.5W 85 KT 100 MPH

$$
Forecaster Blake

[Kazmit]

I'm surprised the wind speed is still at 55 kt. The new track has shifted a bit more west, closer to Bermuda.

FORECAST POSITIONS AND MAX WINDS

INIT 23/2100Z 14.2N 35.8W 55 KT 65 MPH
12H 24/0600Z 15.2N 38.1W 65 KT 75 MPH
24H 24/1800Z 16.8N 40.7W 75 KT 85 MPH
36H 25/0600Z 18.7N 43.2W 80 KT 90 MPH
48H 25/1800Z 20.8N 45.4W 80 KT 90 MPH
72H 26/1800Z 25.5N 49.6W 70 KT 80 MPH
96H 27/1800Z 28.5N 53.5W 75 KT 85 MPH
120H 28/1800Z 31.0N 54.5W 85 KT 100 MPH

[cycloneye]

Weakens a little but intensifies again at day 5.

Gaston has about 24-36
hours to intensify before southwesterly vertical wind shear
associated with a mid-tropospheric trough is forecast to increase.
This shear should result in some weakening of the cyclone in the
2 or 3 day time frame. Thereafter, Gaston moves away from the
trough, and since the cyclone should be over warm waters near 29C,
some restrengthing is likely.

[HurricaneBelle]

I'm surprised the wind speed is still at 55 kt. The new track has shifted a bit more west, closer to Bermuda.

FORECAST POSITIONS AND MAX WINDS

INIT 23/2100Z 14.2N 35.8W 55 KT 65 MPH
12H 24/0600Z 15.2N 38.1W 65 KT 75 MPH
24H 24/1800Z 16.8N 40.7W 75 KT 85 MPH
36H 25/0600Z 18.7N 43.2W 80 KT 90 MPH
48H 25/1800Z 20.8N 45.4W 80 KT 90 MPH
72H 26/1800Z 25.5N 49.6W 70 KT 80 MPH
96H 27/1800Z 28.5N 53.5W 75 KT 85 MPH
120H 28/1800Z 31.0N 54.5W 85 KT 100 MPH

That's still a good 10 degrees east of Bermuda, though. They'll get some serious swells on that track.

[Kazmit]

Should reach it's highest intensity after exiting the shear. Looking good right now, with more convection.

[cycloneye]

Models continue very bullish.They stall the intensity around 72 hours but ramp up again after that time.

[Hybridstorm_November2001]

Satellite presentation is fantastic.

[psyclone]

what a system. we needed a late August long tracker and this one looks good.

[abajan]

It's begun to form a fist in the last few frames:



May be a sign it's about to undergo rapid intensification.

[Yellow Evan]

Code: Select all

 23/2345 UTC   14.3N     36.1W       T3.0/4.0         GASTON -- Atlantic 

Why use curved band pattern given it's clearly not weakened the past 12 hours?

[HurricaneRyan]

Definitely the most exciting storm of the season so far

[Yellow Evan]

Code: Select all

                    * ATLANTIC     SHIPS INTENSITY FORECAST          *
                    * IR SAT DATA AVAILABLE,       OHC AVAILABLE     *
                    *  GASTON      AL072016  08/24/16  00 UTC        *

TIME (HR)          0     6    12    18    24    36    48    60    72    84    96   108   120
V (KT) NO LAND    55    58    61    65    67    67    64    63    69    75    82    86    88
V (KT) LAND       55    58    61    65    67    67    64    63    69    75    82    86    88
V (KT) LGEM       55    57    60    63    64    65    61    59    60    67    79    90    93
Storm Type      TROP  TROP  TROP  TROP  TROP  TROP  TROP  TROP  TROP  TROP  TROP  TROP  TROP

SHEAR (KT)         2     3     9     9    10    22    28    20     5     6     8    10    16
SHEAR ADJ (KT)     0     3     2     2     5     6     5    -1    -1    -8    -4    -2     0
SHEAR DIR         56   307   305   297   279   259   237   213   197   311   292   324   301
SST (C)         27.2  27.0  26.8  26.6  26.6  27.2  27.5  27.8  28.4  28.9  29.2  29.2  28.8
POT. INT. (KT)   129   126   124   122   122   128   132   136   144   150   154   154   147
ADJ. POT. INT.   128   124   121   119   118   123   125   127   131   131   132   129   123
200 MB T (C)   -53.0 -53.1 -53.2 -52.9 -53.2 -53.7 -54.3 -54.5 -54.3 -54.3 -53.6 -52.9 -52.5
200 MB VXT (C)  -0.2  -0.1   0.0   0.1   0.3   0.4   0.5   0.5   0.4   0.0   0.5   1.0   1.9
TH_E DEV (C)       7     7     8     8     8     8     8     8     9     9    10    10    10
700-500 MB RH     66    67    68    67    67    67    68    66    63    60    56    58    56
MODEL VTX (KT)    20    21    23    24    24    24    22    22    25    26    30    32    34
850 MB ENV VOR   105    96    86    68    50    24    18    11    25    16    10    14     3
200 MB DIV        14    41    69    90   103    88    65    22    28    20    23    27     1
700-850 TADV       0     0     2     3     5    23    38    35    -4    -2     0     0     4
LAND (KM)       1979  1903  1841  1828  1827  1847  1977  1917  1788  1713  1667  1734  1643
LAT (DEG N)     14.4  15.1  15.7  16.7  17.6  19.5  21.8  24.2  26.3  27.8  28.8  30.1  31.5
LONG(DEG W)     36.5  37.9  39.3  40.5  41.8  44.2  46.2  48.3  50.6  52.5  54.0  54.5  54.1
STM SPEED (KT)    16    15    15    15    15    15    15    15    13    10     7     6     7
HEAT CONTENT      11    12    12     7    13    10     5    22    34    26    29    28    25

  FORECAST TRACK FROM OFCI      INITIAL HEADING/SPEED (DEG/KT):290/ 16      CX,CY: -14/  5
  T-12 MAX WIND:  55            PRESSURE OF STEERING LEVEL (MB):  546  (MEAN=618)
  GOES IR BRIGHTNESS TEMP. STD DEV.  50-200 KM RAD:  12.6 (MEAN=14.5)
  % GOES IR PIXELS WITH T < -20 C    50-200 KM RAD:  76.0 (MEAN=65.0)
  PRELIM RI PROB (DV .GE. 30 KT IN 24 HR):            7.5

                        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.  11.  11.  12.  13.  13.
  SST POTENTIAL          1.   2.   2.   3.   3.   4.   4.   5.   5.   5.   5.   4.
  VERTICAL SHEAR MAG     1.   2.   2.   3.   2.   0.  -1.   1.   3.   4.   4.   4.
  VERTICAL SHEAR ADJ     0.   0.   0.  -1.  -1.  -2.  -2.  -2.   0.   1.   1.   1.
  VERTICAL SHEAR DIR     0.   0.   0.   0.  -1.  -2.  -2.  -2.  -2.  -2.  -2.  -2.
  PERSISTENCE            0.  -1.  -1.  -1.  -1.  -1.  -1.  -1.   0.   0.   0.   0.
  200/250 MB TEMP.       0.  -1.  -1.  -2.  -2.  -1.  -1.  -1.  -1.   0.   0.  -1.
  THETA_E EXCESS         0.   0.   0.   0.   0.   0.   0.   0.   0.   0.   0.   0.
  700-500 MB RH          0.   0.   0.  -1.  -1.  -2.  -3.  -4.  -4.  -4.  -4.  -4.
  MODEL VTX TENDENCY     0.   1.   2.   2.   2.   0.  -1.   2.   4.   7.  10.  11.
  850 MB ENV VORTICITY   0.   1.   1.   1.   1.   1.   1.   1.   1.   1.   1.   0.
  200 MB DIVERGENCE      0.   0.   0.   1.   1.   1.   1.   1.   1.   0.   0.  -1.
  850-700 T ADVEC        0.   0.   0.   0.   0.   1.   2.   2.   1.   1.   1.   1.
  ZONAL STORM MOTION     0.   0.   1.   1.   2.   2.   2.   3.   3.   3.   4.   4.
  STEERING LEVEL PRES    0.   0.   0.   0.   1.   1.   1.   1.   1.   1.   1.   1.
  DAYS FROM CLIM. PEAK   0.   0.   0.   0.   0.   0.   0.   0.   0.   0.   0.   0.
  GOES PREDICTORS        0.   1.   1.   1.   1.   1.   1.   0.   0.   0.   0.   0.
  OCEAN HEAT CONTENT     0.   0.   0.   0.  -1.  -1.  -1.  -1.  -1.  -1.  -1.  -1.
                        ----------------------------------------------------------
  TOTAL CHANGE           3.   6.  10.  12.  12.   9.   8.  14.  20.  27.  31.  33.

                CURRENT MAX WIND (KT):   55. LAT, LON:   14.4    36.5

      ** 2015 ATLANTIC RI INDEX AL072016 GASTON     08/24/16  00 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):     0.0     -49.5  to   33.0       0.60           3.9
 850-200 MB SHEAR (KT) :     6.7      28.8  to    2.9       0.85           2.4
 HEAT CONTENT (KJ/cm2) :    11.0       0.0  to  155.1       0.07           0.2
 STD DEV OF IR BR TEMP :    12.6      37.5  to    2.9       0.72           2.0
 2nd PC OF IR BR TEMP  :     0.2       2.8  to   -3.1       0.45           1.2
 MAXIMUM WIND (kt)     :    55.0      22.5  to  121.0       0.92           0.9
 D200 (10**7s-1)       :    63.4     -23.1  to  181.5       0.42           0.5
 POT = MPI-VMAX (KT)   :    67.2      28.4  to  139.1       0.35           0.6
 % AREA WITH TPW <45 mm:     0.0     100.0  to    0.0       1.00           0.7
 BL DRY-AIR FLUX (w/m2):   266.0     960.3  to  -67.1       0.68           0.0
 
 SHIPS Prob RI for 20kt/ 12hr RI threshold=   7% is   1.3 times sample mean ( 5.5%)
 SHIPS Prob RI for 25kt/ 24hr RI threshold=  22% is   1.9 times sample mean (11.6%)
 SHIPS Prob RI for 30kt/ 24hr RI threshold=  12% is   1.7 times sample mean ( 7.2%)
 SHIPS Prob RI for 35kt/ 24hr RI threshold=  12% is   2.9 times sample mean ( 4.2%)
 SHIPS Prob RI for 40kt/ 24hr RI threshold=  10% is   3.6 times sample mean ( 2.8%)
 SHIPS Prob RI for 45kt/ 36hr RI threshold=  14% is   2.8 times sample mean ( 4.9%)
 SHIPS Prob RI for 55kt/ 48hr RI threshold=  16% is   3.2 times sample mean ( 5.1%)
 
 Matrix of RI probabilities
 ---------------------------------------------------------------------
  RI (kt / h)  | 20/12 | 25/24 | 30/24 | 35/24 | 40/24 | 45/36 | 55/48
 ---------------------------------------------------------------------
   SHIPS-RII:     7.1%   21.7%   12.4%   12.4%   10.1%   14.0%   16.5%
    Logistic:     4.6%   12.7%    5.6%    2.9%    0.0%    1.8%    0.7%
    Bayesian:     1.9%    2.7%    0.8%    0.2%    0.1%    0.4%    0.3%
   Consensus:     4.5%   12.4%    6.3%    5.1%    3.4%    5.4%    5.8%

   ##         ANNULAR HURRICANE INDEX (AHI) AL072016 GASTON     08/24/16  00 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 AL072016 GASTON     08/24/2016  00 UTC **
TIME(HR)   0-12  12-24(0-24)  24-36(0-36)  36-48(0-48)
CLIMO(%)     0      0(  0)       3(  3)       3(  6)     <-- 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)  55    58    61    65    67    67    64    63    69    75    82    86    88
 18HR AGO           55    54    57    61    63    63    60    59    65    71    78    82    84
 12HR AGO           55    52    51    55    57    57    54    53    59    65    72    76    78
  6HR AGO           55    49    46    45    47    47    44    43    49    55    62    66    68
      NOW                              CURRENT INTENSITY < 83 KT
  IN  6HR                              INTENSITY IN  6HR < 83 KT
  IN 12HR                              INTENSITY IN 12HR < 83 KT

[cycloneye]

TROPICAL STORM GASTON DISCUSSION NUMBER 6
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016
1100 PM AST TUE AUG 23 2016

Gaston's cloud pattern has a figure-nine appearance, with an
apparent dry slot over the southwest quadrant, and lacks a
well-defined CDO at this time. The intensity is held at 55 kt in
agreement with subjective and objective Dvorak estimates. The
system has fairly well-defined upper-level outflow and is expected
to remain in a low-shear environment for the next day or so.
Therefore, the cyclone is likely to intensify into a hurricane in 12
to 24 hours. In about 36 hours, however, Gaston should encounter
increasing southwesterly shear associated with an upper-tropospheric
trough near 50-55W. This should at least temporarily halt the
intensification process, and probably cause a little weakening.
The global models indicate that Gaston will pass by the trough in 72
hours, and reintensification should commence around that time. The
official intensity forecast is near the high end of the guidance
models through 72 hours, and close to the model consensus
thereafter.

The motion continues toward the west-northwest, or 290/15 kt.
Gaston should gradually turn toward the northwest in response to a
break in the subtropical ridge near 60W. The official track
forecast, which is very similar to the previous one, follows the
latest dynamical model consensus, TVCN.

FORECAST POSITIONS AND MAX WINDS

INIT 24/0300Z 14.7N 37.1W 55 KT 65 MPH
12H 24/1200Z 15.8N 39.2W 65 KT 75 MPH
24H 25/0000Z 17.5N 41.7W 70 KT 80 MPH
36H 25/1200Z 19.5N 44.1W 75 KT 85 MPH
48H 26/0000Z 22.0N 46.2W 75 KT 85 MPH
72H 27/0000Z 26.5N 51.0W 70 KT 80 MPH
96H 28/0000Z 29.5N 54.5W 75 KT 85 MPH
120H 29/0000Z 31.5N 55.0W 85 KT 100 MPH

$$
Forecaster Pasch

[cycloneye]

This is why they not upgraded yet to Hurricane.

Gaston's cloud pattern has a figure-nine appearance, with an
apparent dry slot over the southwest quadrant, and lacks a
well-defined CDO at this time.

[Hammy]

That outflow to the NW isn't expanding outward anymore and is just straight SW-NE--I think 99L is going to end up causing some shear trouble for this over the next few days and I wouldn't be surprised if it is at a short-term peak at the moment should this be the case.

[SeGaBob]

Definitely the most exciting storm of the season so far

Not even close

[Blinhart]

Definitely the most exciting storm of the season so far

Not even close

Not anymore, future Hermine will be making this board go nuts.