CPAC: DARBY - Post-Tropical

[cycloneye]

TROPICAL STORM DARBY DISCUSSION NUMBER 55
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP052016
1100 PM HST SUN JUL 24 2016

Bands of heavy rain with embedded strong thunderstorms have been
developing to the north through southeast of Darby's center
over the past several hours, with some of these bands causing
significant flooding impacts over the island of Oahu. The
subjective Dvorak intensity estimates from HFO/SAB/GTW all indicated
a current intensity of 2.0/30 kt. However, the current intensity
will be maintained at 35 kt for this advisory due to the strong
thunderstorms leading to tropical storm conditions over areas to the
north through southeast of the center.

The initial motion vector for this advisory 325/10 kt, with Darby
becoming increasingly shallow as it is embedded in an environment
characterized by strong southwesterly shear. Although SHIPS
guidance reduces the shear on days 2 and 3, Darby is not expected to
survive the trek over increasingly cooler waters, and degeneration
to a post-tropical low is expected relatively soon. Global models
indicate Darby will track toward the northwest before weakening to a
trough by day 3, and the official forecast follows closely. The
updated track forecast follows the trajectory of the previous
closely, except for a slight westward shift in order to come in line
with the latest GFEX guidance.


FORECAST POSITIONS AND MAX WINDS

INIT 25/0900Z 22.4N 159.4W 35 KT 40 MPH
12H 25/1800Z 23.3N 160.3W 30 KT 35 MPH
24H 26/0600Z 24.4N 161.7W 30 KT 35 MPH
36H 26/1800Z 25.6N 163.1W 30 KT 35 MPH...POST-TROP/REMNT LOW
48H 27/0600Z 27.1N 164.4W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 28/0600Z...DISSIPATED

$$
Forecaster Birchard

[cycloneye]

TROPICAL DEPRESSION DARBY DISCUSSION NUMBER 56
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP052016
500 AM HST MON JUL 25 2016

Areas of heavy rain and strong thunderstorms continue to develop to
the north through east of Darby's poorly-defined center as it
interacts with a sharp trough aloft, and the system is in the
process of losing tropical characteristics. The center passed very
close to the island of Kauai overnight, but appeared to remain
offshore before taking a turn toward the west-northwest. Subjective
Dvorak intensity estimates for this forecast cycle ranged from
1.5/25 kt from SAB, to 2.0/30 kt from HFO, to 2.5/35 kt from GTW.
Based on a blend of those estimates, the initial intensity for
this advisory is 30 kt.

The initial motion vector is estimated to be 280/10 kt, as an
increasingly shallow and poorly-defined Darby is now being steered
by the low-level trade wind flow. Strong southwesterly shear will
preclude re-organization, and Darby is expected to move toward the
west-northwest, then northwest, toward a weakness in the low-level
ridge to its north. On this track, water temperatures will
gradually cool, and Darby is expected to soon become a post-tropical
remnant low, with dissipation expected shortly thereafter, close to
the LGEM intensity guidance. The updated forecast track was shifted
to the left of the previous to account for the current motion, and
lies close to the EMXI.


FORECAST POSITIONS AND MAX WINDS

INIT 25/1500Z 22.4N 160.6W 30 KT 35 MPH
12H 26/0000Z 23.1N 162.0W 30 KT 35 MPH
24H 26/1200Z 24.2N 163.6W 25 KT 30 MPH...POST-TROP/REMNT LOW
36H 27/0000Z 25.5N 165.2W 20 KT 25 MPH...POST-TROP/REMNT LOW
48H 27/1200Z...DISSIPATED

$$
Forecaster Birchard

[cycloneye]

TROPICAL DEPRESSION DARBY DISCUSSION NUMBER 57
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP052016
1100 AM HST MON JUL 25 2016

The low level center of Darby appeared to be trackable from
satellite, surface observations on Kauai, and helpful reports from
the NOAA ship Hiialakai overnight. Visible imagery this morning
shows Darby as a low level swirl west of Niihau and becoming
increasingly seperated from deep convection well north of Oahu. The
satellite-based current intensity estimates were 2.0 from CPHC and
JTWC, and 1.5 from SAB. There were some believable 30 kt winds
northeast of the center from the 16 UTC RapidScat pass, so the
intensity for this advisory will be maintained at 30 kt.

Shear has taken its toll on Darby and it seems quite unlikely that
the system will be able to recover. The remnant circulation will be
steered in part by the low level easterlies. Have adjusted the
forecast slightly to the left of the previous official forecast to
account for this as well as recent motion, which has been somewhat
erratic. Darby is expected to be a post-tropical remnant low within
12 hours, followed by dissipation by Tuesday.

FORECAST POSITIONS AND MAX WINDS

INIT 25/2100Z 22.2N 161.0W 30 KT 35 MPH
12H 26/0600Z 22.6N 162.1W 30 KT 35 MPH...POST-TROP/REMNT LOW
24H 26/1800Z 23.5N 163.9W 25 KT 30 MPH...POST-TROP/REMNT LOW
36H 27/0600Z...DISSIPATED

$$
Forecaster R Ballard

[1900hurricane]

The Himawari-8 Loop of the Day is of Darby.

Linked because It's a massive loop

[cycloneye]

POST-TROPICAL CYCLONE DARBY DISCUSSION NUMBER 58
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP052016
500 PM HST MON JUL 25 2016

Darby is an elliptical low-level swirl devoid of persistent deep
convection. All 3 satellite agencies considered the system too weak
to classify. A combination of moderate shear and cooler waters along
the expected track of the feature makes regeneration unlikely.
Thus, the system is being declared a post-tropical remnant low with
this advisory. The remnants of Darby are expected to become a
trough which should continue tracking toward the west-northwest
toward a weakness in the subtropical ridge over the next couple of
days.

This will be the last advisory issued by the Central Pacific
Hurricane Center on Darby unless regeneration occurs. Additional
information on this system can be found in the High Seas Forecasts
issued by the National Weather Service in Honolulu under AWIPS
header HFOHSFNP and WMO header FZPN40 PHFO.


FORECAST POSITIONS AND MAX WINDS

INIT 26/0300Z 22.6N 161.8W 25 KT 30 MPH...POST-TROP/REMNT LOW
12H 26/1200Z 23.3N 163.0W 20 KT 25 MPH...POST-TROP/REMNT LOW
24H 27/0000Z...DISSIPATED

$$
Forecaster R Ballard