CPAC: MIRIAM - Post-Tropical

[HurricaneRyan]

Such a polar opposite from Norman. Crazy

[cycloneye]

Hurricane Miriam Discussion Number 20
NWS Central Pacific Hurricane Center Honolulu HI EP152018
500 PM HST Thu Aug 30 2018

Deep convection has been pulsing and producing bursts of lightning
near the center of Miriam today, but after a brief sighting this
morning, an eye has not reappeared in traditional satellite
imagery. Dvorak current intensity estimates from HFO/SAB/GTW remain
4.5/77 kt, and with little overall change in the satellite
presentation from earlier today, the initial intensity will remain
75 kt for this advisory.

The initial motion estimate is 350/07 kt. A motion toward the north
will continue over the next 36 to 48 h, as Miriam is carried by the
gradient between a deep-layer ridge to the east and a deep-layer
trough to the north. Decreasing SSTs and increasingly strong
southwesterly vertical wind shear lie along the forecast path, and
Miriam's time as a tropical cyclone is limited. Gradual weakening
in the short term is expected to be followed by a more rapid rate
of decay between 24 h and 72 h, and Miriam is expected to become a
post-tropical remnant low on day 3, dissipating by day 5. As Miriam
weakens, it is expected to turn toward the northwest as it becomes
shallow and steered by the low-level trade flow. Track model
guidance is in better agreement as compared to 24 h ago, with the
GFS shifting markedly poleward over the past several runs, closer
to the other reliable dynamical aids. The CPHC track forecast was
shifted to the right of the previous and very closely mimics TVCE
and HCCA. The intensity forecast follows trends presented by all
reliable guidance.


FORECAST POSITIONS AND MAX WINDS

INIT 31/0300Z 16.5N 141.6W 75 KT 85 MPH
12H 31/1200Z 17.9N 141.4W 70 KT 80 MPH
24H 01/0000Z 19.7N 141.5W 65 KT 75 MPH
36H 01/1200Z 21.5N 141.9W 50 KT 60 MPH
48H 02/0000Z 23.2N 143.0W 40 KT 45 MPH
72H 03/0000Z 26.6N 146.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 04/0000Z 30.0N 150.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 05/0000Z...DISSIPATED

$$
Forecaster Birchard

[cycloneye]

Hurricane Miriam Discussion Number 21
NWS Central Pacific Hurricane Center Honolulu HI EP152018
1100 PM HST Thu Aug 30 2018

The satellite presentation of Miriam has changed little over the
past 6 hours, but a slight improvement in the convective cloud
coverage over the low level circulation center appears to have
occurred during the past several hours. A large area of -65 to -80C
cloud tops remain over the difficult to locate low level circulation
center. Several microwave passes since 30/2330Z have been helpful in
confidently determining the center location of Miriam as well as
estimating the motion of the system this evening, with a 0346Z
Windsat and 0636Z MHS Metop-A pass particularly useful. Subjective
Dvorak fixes from PHFO, SAB, and JTWC all came in with intensity
estimates of 4.5 (77 knots) with the Advanced Dvorak Technique from
UW-CIMSS slightly lower at 4.3 (72 knots). Several images around
31/06Z showed the center sufficiently within the deeper colder cloud
tops to yield a T5.0 (90 knots). Based on the slight improvement in
the convective cloud coverage over Miriam, and several images
around the synoptic hour yielding higher intensity estimates, the
initial intensity for this advisory has been weighted slightly
higher than the intensity estimates indicated from the various
agencies. The initial intensity has been raised to 80 knots with
this advisory with a motion of 360/07 knots.

Miriam is being steered by a large subtropical ridge to the
northeast and a mid-upper level trough to the north and northwest.
A general northward motion is expected to continue tonight through
Friday night as the system remains deep and intact following the
deep layer steering flow. Strong southwesterly shear is then
expected to decouple the system by late Friday night or early
Saturday, and this is expected to result in a turn toward the
northwest with Miriam being steered by the low level trade wind
flow. The official forecast has been shifted slightly to the right
through 48 hours to better align with the HWRF, TVCE, HCCA and GFS
which indicate a fairly deep circulation. Beyond 48 hours the
official forecast track lies roughly on top of the previous forecast
as the system becomes increasingly shallow and steered by the low
level trade wind flow.

It appears that the window for Miriam to intensify has closed, with
the latest UW-CIMSS vertical shear analysis showing 21 knots of
southwesterly shear over the core of the system. The hurricane is
expected to slowly weaken tonight and Friday as shear steadily
increases. Rapid weakening is then forecast Friday night and
Saturday as Miriam moves into a region of strong southwesterly shear
of 35 to 50 knots and moves over unfavorable sea surface
temperatures below 26C. Miriam is forecast to become a remnant low
by late Sunday.


FORECAST POSITIONS AND MAX WINDS

INIT 31/0900Z 17.4N 141.5W 80 KT 90 MPH
12H 31/1800Z 18.7N 141.3W 75 KT 85 MPH
24H 01/0600Z 20.5N 141.5W 65 KT 75 MPH
36H 01/1800Z 22.3N 142.3W 50 KT 60 MPH
48H 02/0600Z 24.2N 143.6W 35 KT 40 MPH
72H 03/0600Z 27.7N 147.3W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 04/0600Z 31.0N 152.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 05/0600Z...DISSIPATED

$$
Forecaster Jelsema

[cycloneye]

Hurricane Miriam Discussion Number 22
NWS Central Pacific Hurricane Center Honolulu HI EP152018
500 AM HST Fri Aug 31 2018

Miriam is beginning to feel the effects of increasing southwesterly
shear, with the latest UW-CIMSS analysis depicting 30 knots of
shear over the system. Despite the increasing shear, the system
continues to hold a large area of deep convection with -65 to -80C
cloud tops over the low level circulation center. The latest
subjective Dvorak intensity estimates from PHFO, SAB, and JTWC all
came in at 4.5 (77 knots) with the Advanced Dvorak Technique from
UW-CIMSS slightly higher 4.6 (80 knots). The initial intensity for
this advisory will be held at 80 knots based on a blend of these
intensity estimates and recent satellite imagery suggesting the
intensity could be as high as T5.0 (90 knots). The motion is
somewhat uncertain given the deep convection over the center of
Miriam and a lack of timely microwave data. Using a combination of
interpolation of the movement when confidence in the center position
was high, along with current satellite trends, the motion is set at
005/09 knots.

Hurricane Miriam is being steered by a large subtropical ridge to
the east and northeast along with a deep mid-upper level trough to
the north and northwest. A general northward motion is expected to
continue today and tonight as the system remains fairly deep and
follows the deep layer steering flow. Strong southwesterly shear is
then expected to decouple the system by late tonight or early
Saturday, and this is expected to result in a turn toward the
northwest with Miriam being steered by the low level trade wind
flow. The official forecast has been nudged slightly to the left
through 24 hours based on the estimated initial motion slightly to
the east of due north. Beyond 24 hours the track forecast lies
virtually on top of the forecast from the previous advisory. The
track forecast closely follows the latest TVCE/HCCA consensus
guidance through 48 hours, then is slightly to the left of the
consensus guidance beyond 48 hours expecting a fairly shallow
system being steered by the trades and more in line with the GFS
solution.

Miriam peaked at an intensity of 80 knots overnight, a high end
category one hurricane, and it appears likely that this will be as
strong as the system gets. Southwesterly shear is forecast to
increase further today, with 35 to 50 knots of shear expected over
the cyclone tonight through the end of the forecast period, while
the system is passing over sea surface temperatures below 26C.
Rapid weakening should begin later today, with Miriam expected to
drop below hurricane strength late today or tonight, and become a
post-tropical remnant low Sunday or Sunday night. The intensity
forecast is closely aligned with the latest dynamical and consensus
guidance which were all in good agreement.


FORECAST POSITIONS AND MAX WINDS

INIT 31/1500Z 18.3N 141.2W 80 KT 90 MPH
12H 01/0000Z 19.6N 141.2W 70 KT 80 MPH
24H 01/1200Z 21.4N 141.7W 55 KT 65 MPH
36H 02/0000Z 23.2N 142.8W 45 KT 50 MPH
48H 02/1200Z 25.1N 144.4W 35 KT 40 MPH
72H 03/1200Z 28.5N 148.4W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 04/1200Z...DISSIPATED

$$
Forecaster Jelsema

[HurricaneRyan]

Miriam is doing pretty ok despite only being a Cat 1

[Kingarabian]

Probably close to major hurricane status if it weren't for constraints:

CI# /Pressure/ Vmax
4.9 / 968.1mb/ 87.4kt


Final T# Adj T# Raw T#
4.9 5.5 5.5

[Kingarabian]

[cycloneye]

Hurricane Miriam Discussion Number 23
NWS Central Pacific Hurricane Center Honolulu HI EP152018
1100 AM HST Fri Aug 31 2018

Miriam has been resilient under increasing vertical wind shear. A
ragged, cloud-filled eye has reappeared, despite southwesterly
vertical wind shear of about 25 to 35 kt according to SHIPS and
CIMSS, respectively. Subjective Dvorak current intensity estimates
came in at 5.0/90 kt across the board from HFO, SAB, and JTWC, while
CIMSS ADT yielded 80 kt. Given the longer term improvement in the
satellite presentation but noting the periodic filling of the eye
during the past several hours, the initial intensity has been raised
to 85 kt, which may be conservative.

The initial motion estimate is slightly east of due north (010
degrees) at 9 kt. An SSMIS pass from 1352Z suggested some tilt
toward the northeast with height, which led to the placement of the
center near the southwestern edge of the eye as seen on
geostationary satellite imagery. Through the next 24 hours, Miriam
will continue to be steered northward by a mid to upper level trough
to the northwest and a deep ridge to the northeast. Later Saturday,
Miriam will begin a turn toward the northwest. This will occur as
the steering flow of the weakening system becomes increasingly
influenced by the low level ridge that will shift to the north of
Miriam. A general northwestward motion is expected to persist until
dissipation. The track was nudged to the right of the prior forecast
and lies near the middle of the guidance envelope, close to HCCA and
TVCE.

The slight increase in intensity will be short-lived. The already
vigorous, southwesterly vertical wind shear will increase through
the next 36 to 48 hours. In addition, SSTs, which are currently
running around 26.5 C, will steadily decrease along the forecast
track. Expect weakening to commence later today, with a sharp
decrease in intensity tonight through Sunday. The intensity
forecast goes nearly down the middle of the guidance envelope and is
close to the statistical models and FSSE. On this forecast, Miriam
will be a tropical storm by Saturday and will weaken to a remnant
low late Sunday or Monday.


FORECAST POSITIONS AND MAX WINDS

INIT 31/2100Z 19.2N 141.1W 85 KT 100 MPH
12H 01/0600Z 20.6N 141.2W 75 KT 85 MPH
24H 01/1800Z 22.6N 141.7W 55 KT 65 MPH
36H 02/0600Z 24.6N 143.0W 40 KT 45 MPH
48H 02/1800Z 26.6N 144.7W 35 KT 40 MPH
72H 03/1800Z 30.0N 148.6W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 04/1800Z...DISSIPATED

$$
Forecaster Wroe

[hurricanes1234]

This basin hasn't ceased to put on a show this month. The monthly ACE in August is almost one and a half average Atlantic seasons. Simply incredible, and there's yet more to come.

[cycloneye]

Hurricane Miriam Discussion Number 24
NWS Central Pacific Hurricane Center Honolulu HI EP152018
500 PM HST Fri Aug 31 2018

Vertical wind shear has begun to take its toll on Miriam. The eye is
no longer present in geostationary satellite imagery, and a
decreasing amount of deep convection has become confined to
the northern semicircle. Subjective Dvorak current intensity
estimates remained at 5.0/90 kt from all fix agencies. However, the
final T numbers were down to 4.0 or 4.5, and given the degradation
of the satellite presentation, the initial intensity will be lowered
to 80 kt. Also, a minor adjustment was made to the wind radii based
on partial ASCAT passes from this morning.

The initial motion estimate is slightly east of due north (010
degrees) at 10 kt. Timely microwave passes (SSMI at 0014Z and SSMIS
at 0106Z) were helpful in placing the center and determining the
short-term motion. Through tonight, Miriam will continue to be
steered northward by a mid to upper level trough to the northwest
and a deep ridge to the northeast. On Saturday, Miriam will begin a
turn toward the northwest. This will occur as the steering flow of
the weakening system becomes increasingly influenced by the low
level ridge that will shift to the north of Miriam. The general
northwestward motion is expected to persist until dissipation. The
track is essentially an update to the prior forecast and is close to
the middle of the guidance envelope near CTCI and HCCA.

Rapid weakening will occur during the next couple of days. The
already vigorous, southwesterly vertical wind shear of 30 to 35 kt
will increase through the next 36 to 48 hours to about 50 kt. In
addition, SSTs, which are currently running around 26.5 C, will
steadily decrease along the forecast track. This will cause Miriam
to weaken to a tropical storm on Saturday and become a remnant low
late Sunday or Monday. The intensity forecast remains in the middle
of the guidance envelope and is close to LGEM through 36 hours,
then remains closer to HWRF.


FORECAST POSITIONS AND MAX WINDS

INIT 01/0300Z 20.1N 141.0W 80 KT 90 MPH
12H 01/1200Z 21.7N 141.1W 65 KT 75 MPH
24H 02/0000Z 23.6N 142.1W 50 KT 60 MPH
36H 02/1200Z 25.6N 143.7W 40 KT 45 MPH
48H 03/0000Z 27.4N 145.6W 35 KT 40 MPH
72H 04/0000Z 30.7N 149.3W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 05/0000Z...DISSIPATED

$$
Forecaster Wroe

[HurricaneRyan]

Miriam did pretty ok for herself

[cycloneye]

Hurricane Miriam Discussion Number 25
NWS Central Pacific Hurricane Center Honolulu HI EP152018
1100 PM HST Fri Aug 31 2018

Miriam's satellite presentation has deteriorated significantly over
the past six hours, with 30 to 35 kt of vertical wind shear
beginning to profoundly affect the core of this tropical cyclone.
Deep convection lies only along the northern flank of the
circulation and outflow has become almost non-existent except to
the north and northeast. Subjective Dvorak current intensity
estimates decreased to 4.5/77 kt from JTWC and SAB, while PHFO
remained at 5.0/90 kt. ADT from UW-CIMSS was 77 kt. Initial
intensity for this advisory is set at 75 kt, which may be high given
what appears to be the beginning of rapid system erosion.

Initial motion is 355/08 kt, based mainly on a 0600 UTC fix
influenced strongly by a 0409 UTC SSMIS pass. Miriam has likely
begun its turn to the north northwest this evening as it is steered
between an upper trough to the northwest and a deep ridge to the
northeast. The track that Miriam actually takes will be determined
by how fast the vertical wind shear decapitates it, with a weaker
Miriam likely forced to turn northwestward faster as system
steering becomes influenced more by low level flow. The track
guidance envelope shifted a bit to the left, likely in anticipation
of more rapid Miriam weakening. The forecast track was shifted
slightly left as well, remaining within the rather tight envelope
between ECMWF and TVCE.

Miriam will continue to weaken in the face of increasing shear and
sub-26 degree C SSTs through the forecast period, with this system
forecast to dissipate at 96 hours. We expect Miriam will weaken to
a tropical storm Saturday before becoming a post tropical remnant
low Monday. While some guidance, like SHIPS, wants to dissipate
Miriam within 48 hours, our intensity forecast follows HWRF between
ECMWF and FSSE.


FORECAST POSITIONS AND MAX WINDS

INIT 01/0900Z 20.9N 141.2W 75 KT 85 MPH
12H 01/1800Z 22.2N 141.6W 65 KT 75 MPH
24H 02/0600Z 24.1N 143.0W 50 KT 60 MPH
36H 02/1800Z 25.9N 144.7W 40 KT 45 MPH
48H 03/0600Z 27.6N 146.5W 35 KT 40 MPH
72H 04/0600Z 30.7N 150.6W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 05/0600Z...DISSIPATED

$$
Forecaster Powell

[wxman57]

Miriam looks closer to a remnant low than a hurricane this morning. Center exposed due to high shear. Limited convection. Bye Miriam.

[cycloneye]

Hurricane Miriam Discussion Number 26
NWS Central Pacific Hurricane Center Honolulu HI EP152018
500 AM HST Sat Sep 01 2018

Shear continues to profoundly affect the core of Miriam this
morning, with the low level circulation center (LLCC) now mostly
exposed along the southwest flank of diminishing deep convection.
UW-CIMSS reports 41 kt of vertical wind shear across this system,
up from 34 kt last evening. Good outflow exists only to the north
through north-northeast, consistent with the shear direction.
Subjective Dvorak current intensity estimates decreased to 4.0/65
kt from PHFO and SAB, and to 3.5/55 kt from JTWC. ADT from UW-CIMSS
was 65 kt. Initial intensity for this advisory is set at 65 kt
which, like last time, represents weakening but may still be a bit
too high given the rapidly deteriorating satellite presentation.

Initial motion is 355/10 kt as Miriam continues northward between
an upper trough to the northwest and a deep ridge to the northeast.
Track guidance continues to depict a turn toward the
north-northwest through Sunday and toward the northwest on Monday.
The guidance envelope is rather tight through 48 hours, with HWRF
depicting a sharper turn toward the left as it forecasts rapid
dissipation of this system and a greater role for low level steering
in the near term. In contrast, ECMWF lies along the right side of
the guidance envelope. The forecast track closely follows the
previous one, neatly following TCVE consensus, but adjusted slightly
to the right through 24 hours to account for initial motion.

Miriam will continue to weaken in the face of increasing shear and
sub-26 degree C SSTs through the forecast period, with this system
forecast to dissipate at 72 hours. We expect Miriam will weaken to
a tropical storm later today before becoming a post tropical
remnant low early Monday. Some guidance dissipate Miriam earlier,
with DSHIP and LGME calling for this at 36 and 48 hours,
respectively. Our intensity curve follows HMNI through 12 hours,
then along HWRF through dissipation.


FORECAST POSITIONS AND MAX WINDS

INIT 01/1500Z 22.2N 141.3W 65 KT 75 MPH
12H 02/0000Z 23.6N 141.9W 55 KT 65 MPH
24H 02/1200Z 25.4N 143.4W 40 KT 45 MPH
36H 03/0000Z 27.1N 145.2W 30 KT 35 MPH
48H 03/1200Z 28.7N 147.2W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 04/1200Z...DISSIPATED

$$
Forecaster Powell

[wxman57]

A hurricane with a raw Dvorak number of 1.5. That's interesting. Dvorak constraints prevent going lower than the 2.8 estimated now. Clearly a highly-sheared TS or depression.

Here's the first visible image. Swirl of low stratus, no convection. A hurricane in name only, it would appear.

[cycloneye]

Tropical Storm Miriam Discussion Number 27
NWS Central Pacific Hurricane Center Honolulu HI EP152018
1100 AM HST Sat Sep 01 2018

Under the effects of strong vertical wind shear, the low level
center of Miriam is now completely exposed, and a diminishing amount
of deep convection is confined to the north quadrant. Subjective
Dvorak current intensity estimates came in at 3.0/45 kt from HFO
and JTWC, while SAB gave a 3.5/55 kt. All final T numbers were
lower. CIMSS ADT yielded a 3.0, and its earlier SATCON from 1642Z
produced 48 kt. Given the significant decay in the satellite
presentation, the initial intensity will be lowered to 50 kt,
making Miriam a rapidly weakening tropical storm.

The initial motion is north-northwest (345 degrees) at 11 kt, and a
turn toward the northwest is under way. A mid to upper level trough
to the northwest of Miriam is producing strong, southwesterly
vertical wind shear of 40 to 50 kt according to analyses, and the
shear will likely continue to increase through the next 18 hours. As
Miriam becomes increasingly shallow and less intense under the
effects of the shear, the system will be steered toward the
northwest under a greater influence of a deep ridge located far to
the northeast. The general northwestward motion will persist through
the duration of the tropical cyclone's existence, which will be a
few days at best. The forecast track lies just right of the middle
of the guidance envelope between HCCA and TVCE. Under the hostile
vertical wind shear and decreasing SSTs, Miriam is expected to
weaken to a post-tropical remnant low on Sunday, with dissipation
likely on Monday. The official forecast weakens Miriam at a slightly
slower rate than most guidance through the next 36 hours and is
close to HMNI and AVNI.



FORECAST POSITIONS AND MAX WINDS

INIT 01/2100Z 23.3N 141.5W 50 KT 60 MPH
12H 02/0600Z 24.7N 142.5W 40 KT 45 MPH
24H 02/1800Z 26.3N 144.1W 30 KT 35 MPH
36H 03/0600Z 27.6N 146.1W 25 KT 30 MPH...POST-TROP/REMNT LOW
48H 03/1800Z 28.7N 148.3W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 04/1800Z...DISSIPATED

$$
Forecaster Wroe

[cycloneye]

Tropical Storm Miriam Discussion Number 28
NWS Central Pacific Hurricane Center Honolulu HI EP152018
500 PM HST Sat Sep 01 2018

The satellite presentation of Miriam continues to steadily
deteriorate under the effects of 45 to 55 kt of southwesterly
vertical wind shear. The center has been completely exposed during
daylight hours, and a diminishing cluster of deep convection in the
north quadrant has been pushed off to more than 100 n mi from the
center. Subjective Dvorak current intensity estimates range from
2.5/35 kt from JTWC and SAB to 3.0/45 kt from HFO. Final T numbers
from all agencies are lower, and CIMSS ADT yielded an estimate of 32
kt. Given these inputs and an 1844Z ASCAT-A pass that showed wind
retrievals near 45 kt, the initial intensity is lowered to 40 kt.
The ASCAT-A pass was also used to adjust the wind radii.

The initial motion is north-northwest (330 degrees) at 11 kt. A mid
to upper level trough to the northwest of Miriam will continue to
produce very strong vertical wind shear during the next couple of
days. As Miriam becomes increasingly shallow under the effects of
the shear, the system will be steered toward the northwest under a
greater influence of a deep ridge located far to the northeast. Once
the turn is made tonight, the general northwestward motion will
persist through dissipation on Monday. The forecast track was nudged
to the left of the prior advisory and lies near the middle of the
guidance envelope near TVCE and HCCA. Under the hostile vertical
wind shear and decreasing SSTs, Miriam is expected to weaken to a
post-tropical remnant low on Sunday. The official forecast weakens
Miriam rather quickly, though at a slightly slower rate than almost
all guidance, and is closest to AVNI.


FORECAST POSITIONS AND MAX WINDS

INIT 02/0300Z 24.2N 142.3W 40 KT 45 MPH
12H 02/1200Z 25.6N 143.6W 35 KT 40 MPH
24H 03/0000Z 27.0N 145.4W 30 KT 35 MPH...POST-TROP/REMNT LOW
36H 03/1200Z 28.2N 147.6W 25 KT 30 MPH...POST-TROP/REMNT LOW
48H 04/0000Z...DISSIPATED

$$
Forecaster Wroe

[AJC3]

Tropical Storm Miriam Discussion Number 29
NWS Central Pacific Hurricane Center Honolulu HI EP152018
1100 PM HST Sat Sep 01 2018

The latest estimates from UW-CIMSS and SHIPS indicate Miriam is
being hammered by 50 to 60 kt of southwesterly vertical wind
shear. As a result, the totally exposed and well defined low-level
circulation center (LLCC) is evident in infrared satellite imagery
this evening. The last hints of deep convection associated with
Miriam are now more than 130 n mi north-northeast of the LLCC.
The latest subjective Dvorak current intensity estimates range from
T2.0/30 kt from JTWC and SAB to T2.5/35 kt from HFO. Final T
numbers from all agencies are lower, and the CIMSS ADT yielded an
estimate of 26 kt. An ASCAT pass from 0557z showed a large area of
30 kt winds east and northeast of the LLCC. Based on a blend of
these estimates, the initial intensity is lowered to 35 kt for
this advisory.

The initial motion is 330 deg / 11 kt. A broad mid- to upper-level
trough to the northwest of Miriam will maintain the very strong
vertical wind shear during the next couple of days. As Miriam
becomes increasingly shallow under the effects of the shear, the
system will likely be steered more toward the northwest under a
greater influence of a deep ridge located far to the northeast.
Once the turn is made later tonight, the general northwestward
motion will likely persist through Monday. The latest forecast
track is close to the previous advisory, and remains near the
middle of the guidance envelope and close to the consensus model
guidance, TVCE and HCCA. Under the hostile vertical wind shear and
decreasing SSTs, Miriam will continue weakening. The latest
intensity forecast weakens Miriam at a slightly slower rate than
almost all of the guidance, and is closest to the GFS model. Note
that Miriam is forecast to be a remnant low by Sunday afternoon or
evening, followed by dissipation on Monday.


FORECAST POSITIONS AND MAX WINDS

INIT 02/0900Z 25.3N 142.9W 35 KT 40 MPH
12H 02/1800Z 26.5N 144.2W 30 KT 35 MPH
24H 03/0600Z 27.9N 146.1W 25 KT 30 MPH...POST-TROP/REMNT LOW
36H 03/1800Z 29.0N 148.3W 25 KT 30 MPH...POST-TROP/REMNT LOW
48H 04/0600Z...DISSIPATED

[cycloneye]

Tropical Depression Miriam Discussion Number 30
NWS Central Pacific Hurricane Center Honolulu HI EP152018
500 AM HST Sun Sep 02 2018

The center of Miriam has been completely devoid of deep
convection for almost 24 hours as nearly 50 kt of southwesterly
vertical wind shear has taken its toll on the system. The latest
subjective Dvorak current intensity estimates range from
unclassifiable by SAB to T1.5/25 kt by JTWC, and T2.0/30 kt by
PHFO. The most recent UW-CIMSS ADT yielded an estimated intensity
of 25 kt. Based on a blend of these estimates, the initial
intensity is lowered to 30 kt for this advisory.

The initial motion is 320 deg / 12 kt. A broad mid- to upper-level
trough to the northwest of Miriam will maintain the very strong
vertical wind shear during the next couple of days. Since Miriam
has transitioned to a shallow low-level cloud swirl, it is now
being steered more toward the northwest under the influence of
a deep subtropical ridge located to the northeast. This
northwestward motion will likely persist through Monday. The latest
forecast track is close to the previous advisory, and remains near
the middle of the guidance envelope and close to the consensus model
guidance, TVCE and HCCA. Under the hostile vertical wind shear and
decreasing SSTs, Miriam will continue weakening. The latest
intensity forecast weakens Miriam at a slightly slower rate than
almost all of the guidance, and is closest to the GFS output. Note
that Miriam is forecast to become a remnant low later today,
followed by dissipation late Monday.


FORECAST POSITIONS AND MAX WINDS

INIT 02/1500Z 26.1N 143.9W 30 KT 35 MPH
12H 03/0000Z 27.3N 145.3W 25 KT 30 MPH...POST-TROP/REMNT LOW
24H 03/1200Z 28.6N 147.4W 25 KT 30 MPH...POST-TROP/REMNT LOW
36H 04/0000Z 29.7N 149.6W 25 KT 30 MPH...POST-TROP/REMNT LOW
48H 04/1200Z...DISSIPATED

$$
Forecaster Houston

[HurricaneRyan]

Bye Miriam