EPAC: EUGENE - Post-Tropical - Discussion

[cycloneye]

TXPZ22 KNES 061223
TCSENP

A. 06E (EUGENE)

B. 06/1200Z

C. 21.1N

D. 110.4W

E. FIVE/GOES-E

F. T3.0/3.0

G. IR/EIR/SWIR

H. REMARKS...6/10 BANDING ON A LOG10 SPIRAL YIELDS A DT OF 3.0. MET IS
2.5 DUE TO A DEVELOPING TREND OVER THE LAST 24 HOURS. PT AGREES WITH
DT. THE FT IS BASED ON THE PT DUE TO BANDING FEATURES NOT BEING CLEAR
CUT AND UNCERTAINTY IN THE CENTER POSITION.

I. ADDL POSITIONS

NIL


...NGUYEN

[cycloneye]

Almost a hurricane.

EP, 06, 2023080612, , BEST, 0, 214N, 1107W, 60, 992, TS

[Extratropical94]

SSD ADT estimates have been slowly creeping into the T4.x region

[cycloneye]

Tropical Storm Eugene Discussion Number 5
NWS National Hurricane Center Miami FL EP062023
900 AM MDT Sun Aug 06 2023

Eugene is on the verge of becoming a hurricane this morning.
Scatterometer data from overnight indicated that the maximum winds
were 55-60 kt, and a GMI microwave pass now shows the development of
a partial eyewall. The storm isn't as impressive on conventional
satellite imagery, however, with the central dense overcast
weakening during the past several hours. Intensity estimates range
from 45-60 kt, and 60 kt is chosen as the initial wind speed, based
on the improved microwave structure and overnight scatterometer
data.

The storm has today to strengthen in marginally conducive
conditions before it crosses over very cool waters overnight.
Eugene should weaken steadily on Monday and Tuesday due to the lack
of instability over the cool waters. Most of the guidance shows
Eugene losing deep convection in 36-48 hours over sub-23C waters,
so post-tropical status is moved up to day 2 in this forecast. No
significant changes were made to the intensity forecast, which
remains close to the intensity consensus.

Microwave data show that Eugene is moving faster to the west-
northwest at about 16 kt. This general motion is anticipated with
some reduction in forward speed during the next day or two while the
storm moves on the southern side of a mid-level ridge. Eugene
should reach the western periphery of the ridge on Tuesday, which
will cause the weakening system to turn and move more slowly
northward. Model guidance has trended westward on this advisory,
and the official forecast follows the trend at longer range. The
global models degenerate the system into a trough in 3-4 days.

Eugene will likely produce areas of heavy rains and gusty winds
across southern portions of the Baja California Sur today as it
passes to the south of the peninsula. Interests there should
monitor the progress of this system.


FORECAST POSITIONS AND MAX WINDS

INIT 06/1500Z 21.8N 111.5W 60 KT 70 MPH
12H 07/0000Z 22.9N 113.8W 65 KT 75 MPH
24H 07/1200Z 24.2N 117.1W 55 KT 65 MPH
36H 08/0000Z 25.2N 119.7W 45 KT 50 MPH
48H 08/1200Z 26.0N 121.4W 35 KT 40 MPH...POST-TROPICAL
60H 09/0000Z 27.0N 121.9W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 09/1200Z 28.0N 121.5W 20 KT 25 MPH...POST-TROP/REMNT LOW
96H 10/1200Z...DISSIPATED

$$
Forecaster Blake

[Sciencerocks]

[Ntxw]

Might be a HU but time is running out.

[Yellow Evan]

Eye feature on vis inspires confidence in a hurricane.

[Yellow Evan]

TXPZ22 KNES 061824
TCSENP

A. 06E (EUGENE)

B. 06/1800Z

C. 22.5N

D. 112.5W

E. FIVE/GOES-E

F. T2.0/3.0

G. IR/EIR/VIS

H. REMARKS...5/10 BANDING ON A LOG10 SPIRAL YIELDS A DT OF 2.5. MET IS
A 2.0 DUE TO A STEADY TREND IN THE SYSTEM OVER THE LAST 24 HOURS. PT
AGREES WITH MET. THE FT IS BASED ON THE MET DUE TO BANDING FEAUTURES
NOT BEING CLEAR CUT.

I. ADDL POSITIONS

NIL


...NGUYEN

[cycloneye]

What? 2.0/3.0 Yellow Evan?

[Sciencerocks]

I'd estimate 65 knots based on the eye feature.

I wouldn't put much credit into these satellite estimates.

[cycloneye]

EP, 06, 2023080618, , BEST, 0, 223N, 1124W, 60, 993, TS

[Ntxw]

[cycloneye]

Tropical Storm Eugene Discussion Number 6
NWS National Hurricane Center Miami FL EP062023
300 PM MDT Sun Aug 06 2023

Eugene is sending some mixed signals this afternoon. While earlier
a possible eye feature was present on the visible imagery, the
feature has weakened and become part of a ragged central dense
overcast. Overall, the system doesn't seem much different than the
last advisory, so 60 kt is maintained on this cycle. The Dvorak
estimate ranges are quite large, with estimates of 40-65 kt, so
the initial wind is a bit more uncertain than average.

The storm should begin to weaken overnight as it crosses a tight
sea-surface temperature gradient, with very cold waters along the
forecast track within 24 h. By early Tuesday, Eugene should
transition to a non-convective post-tropical low, consistent with
the stable environment and the latest global model infrared
satellite forecasts. The new NHC forecast is slightly lower than
the last one, between the model consensus and the NOAA
corrected-consensus prediction.

Eugene is moving along pretty quickly to the west-northwest at
about 17 kt. This motion should continue for about a day until it
reaches the edge of the subtropical ridge. Thereafter, a
weaker cyclone should slow down and turn northward toward a
weakness in the ridge. However, the very hostile environment should
cause what's left of Eugene to stall well west of Baja California
and degenerate to a trough in about 3 days. The latest NHC track
is basically an update of the previous one, close to the eastern
Pacific track consensus TVCE.


FORECAST POSITIONS AND MAX WINDS

INIT 06/2100Z 22.7N 113.2W 60 KT 70 MPH
12H 07/0600Z 23.7N 115.7W 55 KT 65 MPH
24H 07/1800Z 24.9N 118.9W 45 KT 50 MPH
36H 08/0600Z 25.7N 121.1W 35 KT 40 MPH...POST-TROPICAL
48H 08/1800Z 26.5N 122.3W 25 KT 30 MPH...POST-TROP/REMNT LOW
60H 09/0600Z 27.0N 122.0W 20 KT 25 MPH...POST-TROP/REMNT LOW
72H 09/1800Z...DISSIPATED

$$
Forecaster Blake

[cycloneye]

Begins to weaken.

EP, 06, 2023080700, , BEST, 0, 230N, 1142W, 50, 997, TS

[Sciencerocks]

[cycloneye]

Tropical Storm Eugene Discussion Number 7
NWS National Hurricane Center Miami FL EP062023
800 PM PDT Sun Aug 06 2023

Deep convection associated with Eugene has been decreasing as the
cyclone begins to move over cooler waters. There is
significant uncertainty in the current intensity of the storm,
which is set at 50 kt based on a blend of subjective and objective
Dvorak estimates. Given the diminishing convection, this may be a
generous estimate, however.

Eugene continues to move briskly toward the west-northwest with an
initial motion estimate of 295/17 kt. A pronounced weakness in the
mid-level subtropical ridge along 120W-125W should cause the
cyclone to slow down considerably in 24 to 36 hours. Thereafter
Eugene is likely to turn northward into the weakness, and by 48-60
hours, the system should drift slowly as the steering currents
collapse. The official track forecast follows the corrected
multi-model consensus, HCCA, and is quite similar to the previous
NHC prediction.

The cyclone will be moving over progressively cooler waters and
into an increasingly drier air mass. Thus Eugene should continue
to weaken and degenerate into a post-tropical remnant low pressure
system in 36 hours, or sooner. The NHC intensity forecast is close
to the model consensus, IVCN. Given the recent decay of
convection, however, the system could weaken even faster than
shown here.


FORECAST POSITIONS AND MAX WINDS

INIT 07/0300Z 23.3N 115.0W 50 KT 60 MPH
12H 07/1200Z 24.3N 117.5W 40 KT 45 MPH
24H 08/0000Z 25.3N 120.1W 30 KT 35 MPH
36H 08/1200Z 26.1N 121.7W 25 KT 30 MPH...POST-TROP/REMNT LOW
48H 09/0000Z 26.8N 122.2W 25 KT 30 MPH...POST-TROP/REMNT LOW
60H 09/1200Z 27.5N 122.0W 20 KT 25 MPH...POST-TROP/REMNT LOW
72H 10/0000Z...DISSIPATED

$$
Forecaster Pasch

[cycloneye]

Tropical Storm Eugene Discussion Number 8
NWS National Hurricane Center Miami FL EP062023
200 AM PDT Mon Aug 07 2023

Deep convection has been withering away, and Eugene is getting
closer to becoming a post-tropical cyclone. Even though the system
is producing a minimal amount of convection, an ASCAT-B pass
indicated that there is still a considerable area of
tropical-storm-force winds near the center. The maximum winds in
the pass were in the 40-45 kt range, and based on that data, the
initial intensity is nudged downward to 45 kt. This intensity value
is higher than the Dvorak estimates.

Eugene is currently over cool 24 degree C waters and is headed over
progressively cooler waters during the next few days. These
unfavorable oceanic conditions combined with dry air and moderate
shear should cause the storm to continue to steadily weaken.
Eugene is expected to become a post-tropical cyclone in 12 to 24
hours and dissipate entirely in 2 to 3 days.

Eugene is moving quickly to the west-northwest at 18 kt on the
southwest side of a strong mid-level ridge. This motion should
continue today, but a significant slow down and turn to the north
are expected on Tuesday and Wednesday as the ridge breaks down.
The NHC track forecast is similar to the previous one and near the
various consensus models.


FORECAST POSITIONS AND MAX WINDS

INIT 07/0900Z 23.9N 116.9W 45 KT 50 MPH
12H 07/1800Z 24.8N 119.3W 35 KT 40 MPH
24H 08/0600Z 25.7N 121.4W 30 KT 35 MPH...POST-TROP/REMNT LOW
36H 08/1800Z 26.3N 122.3W 25 KT 30 MPH...POST-TROP/REMNT LOW
48H 09/0600Z 26.9N 122.4W 20 KT 25 MPH...POST-TROP/REMNT LOW
60H 09/1800Z...DISSIPATED

$$
Forecaster Cangialosi

[cycloneye]

Tropical Storm Eugene Discussion Number 9
NWS National Hurricane Center Miami FL EP062023
800 AM PDT Mon Aug 07 2023

Eugene has lacked deep convection for at least 7 hours now. Since
the tropical storm is moving over waters of 23 deg C or cooler,
redevelopment of convection is not expected, and it will likely be
classified as a post-tropical cyclone this afternoon. The initial
intensity has been lowered to 40 kt, based on the assumption that
the winds have decreased since the last advisory with no deep
convection to sustain the cyclone, and this could be generous.
Additional weakening appears inevitable, and Eugene is forecast to
dissipate by mid-week.

Eugene continues to move west-northwestward, steered by a strong
low- to mid-level ridge to its northeast. Eugene will likely slow
down significantly by tonight while it weakens, and turn northward
through mid-week. No changes of note were made to the NHC track
forecast.


FORECAST POSITIONS AND MAX WINDS

INIT 07/1500Z 24.5N 118.8W 40 KT 45 MPH
12H 08/0000Z 25.3N 120.5W 30 KT 35 MPH...POST-TROP/REMNT LOW
24H 08/1200Z 26.1N 122.1W 25 KT 30 MPH...POST-TROP/REMNT LOW
36H 09/0000Z 26.6N 122.6W 20 KT 25 MPH...POST-TROP/REMNT LOW
48H 09/1200Z 27.4N 122.4W 20 KT 25 MPH...POST-TROP/REMNT LOW
60H 10/0000Z...DISSIPATED

$$
Forecaster D. Zelinsky

[Sciencerocks]

[cycloneye]

Post-Tropical Cyclone Eugene Discussion Number 10
NWS National Hurricane Center Miami FL EP062023
200 PM PDT Mon Aug 07 2023

Eugene has not had any organized deep convection for over 12 hours
now, and since it is over very cold water, no further thunderstorm
activity is anticipated. Thus, Eugene has transitioned into a
post-tropical cyclone, and this is the last NHC advisory. The
initial wind speed is reduced to 30 kt, in accordance with the
remaining Dvorak estimates. The system should gradually spin down
and become a trough of low pressure in about 2 days. The remnants
of Eugene should turn northward tomorrow into a break in the
low- level ridge and slow down as it gets caught in weak steering
flow. No significant changes were made to the NHC track or
intensity forecasts.

For additional information on the remnant low please see High Seas
Forecasts issued by the National Weather Service, under AWIPS
header NFDHSFEPI, WMO header FZPN02 KWBC, and on the web at
ocean.weather.gov/shtml/NFDHSFEPI.php


FORECAST POSITIONS AND MAX WINDS

INIT 07/2100Z 25.1N 120.4W 30 KT 35 MPH...POST-TROP/REMNT LOW
12H 08/0600Z 25.7N 121.9W 25 KT 30 MPH...POST-TROP/REMNT LOW
24H 08/1800Z 26.3N 122.7W 20 KT 25 MPH...POST-TROP/REMNT LOW
36H 09/0600Z 27.0N 122.7W 20 KT 25 MPH...POST-TROP/REMNT LOW
48H 09/1800Z 27.8N 121.7W 20 KT 25 MPH...POST-TROP/REMNT LOW
60H 10/0600Z...DISSIPATED

$$
Forecaster Blake