CPAC: DARBY - Post-Tropical

[Kingarabian]

Looks like weakening has begun.

[cycloneye]

HURRICANE DARBY DISCUSSION NUMBER 19
NWS NATIONAL HURRICANE CENTER MIAMI FL EP052016
200 AM PDT SAT JUL 16 2016

Darby appears to be maintaining its strength. Satellite images
indicate that the eye of the hurricane has become a bit more
distinct and circular than it was several hours ago. Although the
cloud tops have warmed a bit in the eyewall, the convective pattern
is quite symmetric. A blend of the latest Dvorak classifications
from TAFB and SAB, and automated values from CIMSS at the University
of Wisconsin support holding the initial intensity at 90 kt.

Although the wind shear is expected to remain light during the next
several days, the oceanic conditions will soon become unfavorable
for strengthening. Sea surface temperatures beneath the hurricane
are expected to fall below 26 deg C in about 12 hours, and Darby is
headed for even cooler waters after that. The cool waters combined
with a progressively drier air mass should induce a gradual
weakening trend beginning later today and continuing during the
next several days. The NHC intensity forecast is largely an update
of the previous one and is not too different from the intensity
model consensus.

Darby has been wobbling around during the past 12-18 hours, but
smoothing through these positions yields an initial motion estimate
of 295/9 kt. A gradual turn toward the west is expected during
the next several days as a mid-level ridge builds to the north of
the tropical cyclone. The model guidance is in fair agreement in
the future track of Darby, and the NHC forecast lies close to the
various consensus aids.

An ASCAT pass from a few hours ago was helpful in estimating the
size of the wind field of Darby.

FORECAST POSITIONS AND MAX WINDS

INIT 16/0900Z 17.6N 123.1W 90 KT 105 MPH
12H 16/1800Z 18.0N 124.4W 85 KT 100 MPH
24H 17/0600Z 18.4N 126.0W 75 KT 85 MPH
36H 17/1800Z 18.8N 127.8W 70 KT 80 MPH
48H 18/0600Z 19.1N 129.8W 65 KT 75 MPH
72H 19/0600Z 19.8N 134.2W 50 KT 60 MPH
96H 20/0600Z 20.1N 138.9W 45 KT 50 MPH
120H 21/0600Z 19.5N 144.0W 40 KT 45 MPH

$$
Forecaster Cangialosi

[Kingarabian]

Almost annular.

[stormwise]

Long way to the Big Island and its all dryair to the west.

[NDG]

Darby may have not gotten to Cat 3 but I give it an A for effort, right when I think it's weakening has begun it shakes the dry air off and looks fairly impressive at least for a couple of hours.

[Yellow Evan]

Code: Select all

 
EP, 05, 2016071612,   , BEST,   0, 177N, 1235W,  90,  972, HU,  34, NEQ,  100,   70,   50,   70, 1011,  240,  20, 110,   0,   E,   0,    ,   0,   0,      DARBY, D,  0,    ,    0,    0,    0,    0, genesis-num, 011,
EP, 05, 2016071612,   , BEST,   0, 177N, 1235W,  90,  972, HU,  50, NEQ,   50,   40,   30,   40, 1011,  240,  20, 110,   0,   E,   0,    ,   0,   0,      DARBY, D,  0,    ,    0,    0,    0,    0, genesis-num, 011,
EP, 05, 2016071612,   , BEST,   0, 177N, 1235W,  90,  972, HU,  64, NEQ,   30,   25,   20,   25, 1011,  240,  20, 110,   0,   E,   0,    ,   0,   0,      DARBY, D,  0,    ,    0,    0,    0,    0, genesis-num, 011,


[Yellow Evan]

----- Current Analysis -----
Date : 16 JUL 2016 Time : 140000 UTC
Lat : 17:54:46 N Lon : 123:42:52 W


CI# /Pressure/ Vmax
5.4 / 963.1mb/ 99.6kt


Final T# Adj T# Raw T#
5.4 5.9 5.9

Estimated radius of max. wind based on IR : 27 km

Center Temp : +9.4C Cloud Region Temp : -63.1C

Scene Type : EYE

[Yellow Evan]

[cycloneye]

HURRICANE DARBY DISCUSSION NUMBER 20
NWS NATIONAL HURRICANE CENTER MIAMI FL EP052016
800 AM PDT SAT JUL 16 2016

Darby continues to have a well-defined 20 n mi wide eye, which is
completely encircled by convective cloud tops as cold as -70C.
Satellite intensity estimates at 1200 UTC were rather conflicting.
Subjective Dvorak numbers increased from six hours ago, but at the
same time objective ADT estimates have decreased. Given this
discrepancy, the initial intensity is kept at 90 kt.

Darby is beginning to move over cooler water, with the eye having
reached the 26C isotherm. Although vertical shear over the cyclone
is expected to be low for the next few days, SSTs will be dropping
to as cold as 23C by 72 hours. Therefore, gradual weakening is
anticipated to begin soon, with Darby likely becoming a tropical
storm in about 48 hours. Increasing shear should then contribute to
a faster weakening rate after 48 hours. The new NHC intensity
forecast is very close to the IVCN intensity consensus during the
entire forecast period, and it is a little lower than the previous
forecast from 36 hours and beyond.

The initial motion is west-northwestward, or 290/9 kt. The
subtropical ridge to the north of Darby is in the process of
weakening due to an amplifying trough along the west coast of the
United States. Therefore, Darby is expected to continue moving
west-northwestward for the next 24 hours. After that time, the
weakening cyclone will come under the influence of lower-level
steering, causing it to move westward through the end of the
forecast period. There is very little spread among the track
models, and the NHC track forecast is just an update of the
previous one.

FORECAST POSITIONS AND MAX WINDS

INIT 16/1500Z 17.8N 123.9W 90 KT 105 MPH
12H 17/0000Z 18.2N 125.1W 85 KT 100 MPH
24H 17/1200Z 18.6N 126.8W 75 KT 85 MPH
36H 18/0000Z 18.9N 128.7W 65 KT 75 MPH
48H 18/1200Z 19.1N 130.7W 60 KT 70 MPH
72H 19/1200Z 19.7N 135.2W 50 KT 60 MPH
96H 20/1200Z 19.9N 140.0W 40 KT 45 MPH
120H 21/1200Z 19.0N 145.0W 35 KT 40 MPH

$$
Forecaster Berg

[CrazyC83]

I'm thinking that brief peak will result in its post-analysis intensity being raised to 95 kt.

[Kingarabian]

First Vis:

[Kingarabian]

Not feeling that NHC discussion.

No mention of going annular at all.

[Yellow Evan]

Also, ADT's are not falling like they claim.

[1900hurricane]

Playing Devil's Advocate here, technically the ADT CI is lower right now than it was at the time of the last advisory, despite Darby currently having the highest raw T# yet.

[Kingarabian]

Playing Devil's Advocate here, technically the ADT CI is lower right now than it was at the time of the last advisory, despite Darby currently having the highest raw T# yet.

Well why didn't they factor in the ADT CI when it was at 5.6 and 104kts for 6+ hours?

[Yellow Evan]

----- Current Analysis -----
Date : 16 JUL 2016 Time : 143000 UTC
Lat : 17:55:51 N Lon : 123:53:09 W


CI# /Pressure/ Vmax
5.6 / 959.1mb/104.6kt


Final T# Adj T# Raw T#
5.6 5.7 5.7

Estimated radius of max. wind based on IR : 26 km

Center Temp : +9.8C Cloud Region Temp : -61.3C

Scene Type : EYE

[Kingarabian]

4 hours old:

[Yellow Evan]

----- Current Analysis -----
Date : 16 JUL 2016 Time : 150000 UTC
Lat : 17:56:59 N Lon : 124:03:27 W


CI# /Pressure/ Vmax
5.6 / 959.1mb/104.6kt


Final T# Adj T# Raw T#
5.6 5.6 5.6

Estimated radius of max. wind based on IR : 26 km

Center Temp : +10.9C Cloud Region Temp : -59.6C

Scene Type : EYE

[CrazyC83]

Maybe even increase to 100 kt in post-analysis?

[Kingarabian]

Maybe even increase to 100 kt in post-analysis?

Most likely. But they'll likely assign it cat.3 status in the next advisory if Dvorak numbers increase a little but more before then (and Darby not weakening of course).