CPAC: DARBY - Post-Tropical

[wxman57]

it has 40 to 50 kt winds at landfall

That could be the peak winds, but average winds around most of the storm should be a good bit less.

[Alyono]

ec is coming in quite a bit weaker

[Alyono]

EC passes south as a collapsing system

[wxman57]

ec is coming in quite a bit weaker

But straight into the Big Island. Maybe the SW edge of the island. Well, next panel came in and the center may pass just south of the Big Island, but it may be torn apart in the process.

[tolakram]

Live visible loop

http://weather.msfc.nasa.gov/cgi-bin/get-goes?satellite=GOES-W%20PACUS&lat=19&lon=-149&info=vis&zoom=1&width=1000&height=800&type=Animation&quality=85&palette=ir1.pal&numframes=14

[gatorcane]

Live visible loop

http://weather.msfc.nasa.gov/cgi-bin/get-goes?satellite=GOES-W%20PACUS&lat=19&lon=-149&info=vis&zoom=1&width=1000&height=800&type=Animation&quality=85&palette=ir1.pal&numframes=14

Looks to be building some storms around the center so maybe it is on an organizing trend.

[Kingarabian]

Looks like a hit near Kona - Big Islands second most populated city.

[Kingarabian]

TS watch for the Big Island.

[gatorcane]

[cycloneye]

TROPICAL STORM DARBY DISCUSSION NUMBER 41
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP052016
1100 AM HST THU JUL 21 2016

Darby's satellite signature has changed little since the last
advisory, with a compact area of deep convection wrapping around
the center, mainly in the northern semicircle. Although subjective
Dvorak fixes from HFO/SAB/GTW all indicated a data-T of 3.0/45 kt,
the initial intensity for this advisory will be maintained at 55 kt.
Reconnaissance aircraft from the 53rd Weather Reconnaissance
Squadron are en route to Hawaii, and initial flights into
Darby are scheduled for this time tomorrow, allowing for a much
better estimate of Darby's actual intensity.

The initial motion for this advisory is estimated to be 260/12 kt,
with Darby being steered by a retrograding mid-level ridge centered
well north of Hawaii. This ridge will be the primary steering
mechanism over the next 48 hours or so, after which time a deep
layer low digging southward will weaken the ridge, causing a
reduction in Darby's forward speed. Between 48 hours and 72 hours,
steering currents are expected to be weak, with Darby still expected
to make a turn toward the northwest. In the longer range, a deep
layer southerly flow should steer Darby more quickly toward the
north and lead to weakening. Latest guidance however has trended
toward a less dramatic turn, and shifted closer to Hawaii. The
updated track forecast is similar to the previous through 48 hours,
after which time it has been shifted closer to Hawaii, in response
to a significant westward shift in most of the reliable guidance,
namely the TVCN and GFEX. The official forecast lies on the right
hand side of the guidance suite, and if model trends continue, the
forecast may need to shifted westward with subsequent forecasts. The
updated track forecast necessitates the issuance of a tropical storm
watch for the Big Island and Maui County.

The intensity forecast is essentially unchanged from the previous,
with light to moderate shear inhibiting strengthening while
Darby traverses slightly warmer water over the next 48 hours.
Gradually cooling water temperatures and increasing shear are
expected to lead to a weakening trend on days 4 and 5, and the
updated forecast is close to the IVCN consensus. Of note, while the
official track forecast indicates Darby tracking over portions of
the Hawaiian Islands, the intensity forecast is thus far not
indicating significant weakening due to interaction with land.

Interests elsewhere in the Hawaiian islands should monitor the
progress of Darby, as it could eventually have impacts on all
islands. Remember, it is important not to focus too closely on the
exact track and intensity forecasts because the average track error
72 hours out is near 100 miles, while the average intensity error is
about 15 kt. In addition, the hazards of a tropical cyclone can
extend over a broad area well away from the center.


FORECAST POSITIONS AND MAX WINDS

INIT 21/2100Z 18.6N 146.6W 55 KT 65 MPH
12H 22/0600Z 18.4N 148.3W 55 KT 65 MPH
24H 22/1800Z 18.3N 150.5W 55 KT 65 MPH
36H 23/0600Z 18.5N 152.1W 55 KT 65 MPH
48H 23/1800Z 18.9N 153.6W 55 KT 65 MPH
72H 24/1800Z 20.3N 155.7W 55 KT 65 MPH
96H 25/1800Z 22.5N 157.9W 50 KT 60 MPH
120H 26/1800Z 25.5N 160.5W 40 KT 45 MPH

$$
Forecaster Birchard

[Kingarabian]

Hawaii has to thank the dry air environment Darby is surrounded by, otherwise it would had made a run to become a hurricane again before affecting Hawaii with warm waters and low shear. IMO.

Agreed. Looking at the latest CIMSS maps, it's <= 10kts under the Big Island. If Darby hooks under the Big Island then it'll give the storm even more time to strengthen before hitting the other islands. The 20kt-30kt shear vector lies proportionally with the islands. So the storm could strengthen quite a bit and not feel the shear until landfall or prelandfall.

So hopefully dry air keeps this storm in check.

[cycloneye]

 https://twitter.com/EricBlake12/status/756205376840736768

[Alyono]

the shear should increase dramatically if this does go south of the Big Island. Would not be much left of it if it went to the other islands

[MGC]

Biggest threat from Darby will be the rains. When I was stationed at Pearl, there were several heavy rain events on Oahu which caused quite a bit of destruction. I remember the ocean waters turned red from the runoff from one of the heavy rains......MGC

[CrazyC83]

Do we have many members in Hawaii? Wondering if an obs/preps thread is warranted.

[gatorcane]

Saved loop

[Kingarabian]

Not exactly 55kts worthy but getting there.

[Alyono]

if it would sustain convection, it could quickly become a hurricane

[Kingarabian]

Convections seems to be expanding. Sign that warm waters are near?

[stormwise]

12Z was south, models not really nailing this storm track fluctuations with each output.