CPAC: NORMAN - Post-Tropical

[Kingarabian]

18z GFS and the past 6 runs trending closer to Hawaii.

[cycloneye]

Hurricane Norman Discussion Number 16
NWS National Hurricane Center Miami FL EP162018
800 PM PDT Fri Aug 31 2018

Several recent microwave passes indicate that Norman continues to
feel the effects of northeasterly shear, with the cyclone vertically
titled and its upper-level core disrupted in the northern
semicircle. Furthermore, the eye of the hurricane has disappeared
on IR and visible imagery. Satellite intensity estimates from
TAFB and SAB have also decreased since the previous advisory, and
therefore, the initial intensity has been decreased to 105 kt, and
this value could be a little generous.

Model guidance continues to indicate moderate northeasterly shear
over the cyclone for the next day or so, which should cause
the gradual weakening to continue. Thereafter, the shear is
forecast to lessen somewhat, but the cyclone is expected to begin
entraining dry air from its surrounding environment. There may be
some time between 24-48 hours when the lessening shear and warm SSTs
could overcome the drier air in the environment to allow for either
a steadying of intensity or perhaps even some slight
re-strengthening. Beyond 48 hours, however, the environment is
forecast to become even drier, which should induce another weakening
trend. The NHC intensity forecast has been changed little through 24
h, but now shows a leveling off of the intensity from 24-48 h.
Steady weakening is still anticipated beyond that time.

The initial motion is estimated to be west-southwest, or 250/7 kt.
Mid- to upper-level ridging that extends west-southwestward from
the Baja California peninsula to just northwest of the cyclone
should steer Norman west-southwestward for the next several hours.
By Saturday morning, the ridge should begin to become oriented more
east-to-west then southeast-to-northwest by Sunday. This will cause
the system to be steered on a more westward then west-northwestward
track with an increase in forward speed over the weekend and into
early next week. The NHC track forecast has been shifted slightly
left and is a little faster than the previous advisory. This
forecast is generally between the previous NHC forecast and the
consensus guidance track. Based on this forecast, Norman is
expected to move into the central Pacific basin by Tuesday.

FORECAST POSITIONS AND MAX WINDS

INIT 01/0300Z 16.3N 122.2W 105 KT 120 MPH
12H 01/1200Z 16.2N 123.6W 95 KT 110 MPH
24H 02/0000Z 16.4N 125.9W 90 KT 105 MPH
36H 02/1200Z 17.0N 128.7W 90 KT 105 MPH
48H 03/0000Z 17.7N 131.8W 90 KT 105 MPH
72H 04/0000Z 19.1N 138.0W 80 KT 90 MPH
96H 05/0000Z 20.3N 142.7W 70 KT 80 MPH
120H 06/0000Z 21.2N 146.3W 65 KT 75 MPH

$$
Forecaster Cangialosi/Latto

[Kingarabian]

GFS ensemble trend:


Big differences between the Euro and GFS in track around hour 120:

[cycloneye]

Hurricane Norman Discussion Number 17
NWS National Hurricane Center Miami FL EP162018
200 AM PDT Sat Sep 01 2018

Norman continues to weaken due to the effects of moderate
northeasterly shear of about 20 kt, as analyzed in SHIPS
diagnostics. The hurricane has taken on a traditional IR shear
pattern structure, with a tight gradient of brightness temperatures
observed up-shear of the estimated center position. Satellite
intensity estimates have continued to drop and no longer support
keeping Norman at major hurricane strength. The initial intensity
has been lowered to 95 kt, just above the latest SATCON estimate,
but this still could be generous.

The shear affecting Norman is expected to continue for at least the
next 24 h. Some of the dynamical models hint that the shear could
relax between 24-48 h, which would likely bring an end to Norman's
weakening trend. While it is not explicitly reflected in the
intensity forecast, a decrease in shear could even allow the
hurricane to briefly restrengthen. Recent microwave imagery
indicates that the mid- to lower-level inner-core and eye of Norman
are still intact. If this structure can survive the next 24 h of
shear, reintensification would be more likely. By 72 h, the
hurricane will reach drier, more stable air and moderate SSTs, and
these factors will likely cause it to steadily weaken through the
remainder of the forecast period.

The cyclone appears to have finally turned westward, and the
initial motion is 265/7 kt. No significant changes have been made
to the track forecast. Norman is still expected to move westward
to west-northwestward for the next several days, steered primarily
by an extensive deep-layer ridge to the north. The models remain
in good agreement on the track of Norman throughout the forecast
period, and the official track forecast is near the middle of the
guidance envelope and very close to the various consensus aids.

FORECAST POSITIONS AND MAX WINDS

INIT 01/0900Z 16.3N 123.0W 95 KT 110 MPH
12H 01/1800Z 16.3N 124.4W 85 KT 100 MPH
24H 02/0600Z 16.6N 126.8W 85 KT 100 MPH
36H 02/1800Z 17.3N 129.8W 85 KT 100 MPH
48H 03/0600Z 18.2N 132.9W 85 KT 100 MPH
72H 04/0600Z 19.9N 139.1W 70 KT 80 MPH
96H 05/0600Z 21.0N 143.5W 65 KT 75 MPH
120H 06/0600Z 21.5N 147.0W 60 KT 70 MPH

$$
Forecaster Zelinsky

[Kingarabian]

06z GFS even closer to the big island. Trend on the GFS isn't too good.

[Kingarabian]

00z EPS had more members showing a Hawaii impact or a closer track.

[xtyphooncyclonex]

Further southwest and stronger this time. Dangerously close.



Nonethless, my gut tells me this could pass to the south instead.

This sounds different compared to the previous storms in the same area where west shifts occurred equated to weakening or a weaker storm itself; it does depend indeed on the steering currents.

[cycloneye]

Hurricane Norman Discussion Number 18
NWS National Hurricane Center Miami FL EP162018
800 AM PDT Sat Sep 01 2018

Although satellite intensity estimates indicate that Norman has
continued to weaken, the weakening trend appears to have abated.
This is based on recent infrared imagery showing a better developed
CDO feature accompanied by improved outflow, and also a well-defined
closed eye now depicted in a 1148Z AMSR and 1158Z SSMIS microwave
satellite images. The initial intensity has been lowered to 90 kt,
which is a blend of the various satellite intensity estimates, with
a little more weight placed on the TAFB estimate of T5.0/90 kt.

Norman's initial motion estimate is 270/10 kt. The aforementioned
eye noted in the microwave passes greatly helped with determining
the cyclone's location and past motion. Other than some slight
forward speed adjustments made in the first 24 hours due to the
faster initial motion, no significant changes were required to the
previous track forecast. Norman is forecast to move westward to
west-northwestward for the next several days as the hurricane moves
along the southern periphery of strong deep-layer ridge to the
north. The models are in excellent agreement on the track of Norman
through 72 h, and then diverge noticeably after that time with the
GFS taking Norman more westward in the general direction of the
Hawaiian Islands, whereas the ECMWF, HWRF, and HMON models keep
Norman well to the northeast of the islands. The official forecast
track lies close to the middle of the tightly packed guidance
envelope through 72 h, and then is close to the consensus aids HCCA
and FSSE after that.

The shear that has been affecting Norman appears to have weakened
some this morning, and that decreasing trend is expected to
continue throughout the forecast period, becoming near zero in
48-72 h according to the ECMWF model. The GFS model shows a
similar decreasing shear trend, but just not as much as the ECMWF
model. The HWRF and HMON models also have the shear decreasing and
do a complete reversal by re-strengthening Norman into a major
hurricane again during the next 24 h, followed by slow weakening
thereafter. For now, the official intensity forecast shows little
change in strength for the next 24 h, followed by slow weakening
during the remainder of the forecast period as the cyclone
encounters drier air and cooler sea-surface temperatures near 26C.

FORECAST POSITIONS AND MAX WINDS

INIT 01/1500Z 16.2N 123.7W 90 KT 105 MPH
12H 02/0000Z 16.3N 125.4W 90 KT 105 MPH
24H 02/1200Z 16.9N 128.2W 90 KT 105 MPH
36H 03/0000Z 17.8N 131.3W 85 KT 100 MPH
48H 03/1200Z 18.7N 134.6W 85 KT 100 MPH
72H 04/1200Z 20.3N 140.6W 70 KT 80 MPH
96H 05/1200Z 21.3N 145.3W 65 KT 75 MPH
120H 06/1200Z 22.0N 148.6W 60 KT 70 MPH

$$
Forecaster Stewart

[xtyphooncyclonex]

12z GFS rolling. Norman makes a turn to the WNW (just like other runs) but past TAU 72, he begins strengthening a bit and turning south of west... Very similar to 06z

[Kingarabian]

Outflow expanding north and south of the system. Past couple of microwave images from about 4 hours ago show the eyewall has recovered and is slowly rebuilding itself.

[cycloneye]

Hurricane Norman Discussion Number 19
NWS National Hurricane Center Miami FL EP162018
200 PM PDT Sat Sep 01 2018

Since the previous advisory, a well-defined closed eye has remained
apparent in microwave satellite data, and a cloud-filled eye has
appeared in visible satellite imagery during the past couple of
hours. Satellite intensity estimated haven't changed since the
previous advisory, so the initial intensity remains 90 kt, which is
supported by a 1501Z SATCON estimate of 88 kt and a Dvorak CI value
of T5.0/90 kt.

Norman's initial motion estimate is now 275/12 kt based on microwave
and visible satellite eye position estimates. There are
no significant changes to the previous track forecast and reasoning.
The hurricane is expected to be steered by a strong deep-layer
subtropical ridge to the north, resulting in a westward motion for
the next 12-24 hours, followed by a west-northwestward motion at a
faster forward speed. The latest model guidance is tightly packed
about the previous forecast track through 96 hours, with much less
divergence after that compared to previous model runs. Therefore,
the new forecast track is essentially just an extension of the
previous advisory track, and lies close to a blend of the HCCA,
FSSE, and TVCE consensus track models.

The GFS and ECMWF models are forecasting the 15-20 kt of vertical
wind shear that has been affecting Norman to steadily decrease for
the next 60-72 hours, possibly becoming near zero if the ECMWF
upper-level wind forecasts verify. Since the hurricane is expected
to remain over 27 deg C and warmer SSTs for the next 48 hours, only
slow weakening is forecast and that is due mainly to occasional
intrusions of drier and more stable air coming in from the
northwest, where a large field of cold-air stratocumulus clouds is
currently lurking close by. The HWRF and HMON models continue to
forecast Norman to re-strengthen into a major hurricane during the
next 24 hours, but this scenario is being discounted at this time
due to Norman's proximity to the aforementioned stratocumulus cloud
field. By 72 hours, increasing southwesterly shear and cooler SSTs
should combine to induce more significant weakening. The NHC
intensity forecast is similar to the HCCA and IVCN consensus model
forecasts.

FORECAST POSITIONS AND MAX WINDS

INIT 01/2100Z 16.3N 125.1W 90 KT 105 MPH
12H 02/0600Z 16.6N 127.0W 90 KT 105 MPH
24H 02/1800Z 17.4N 130.1W 85 KT 100 MPH
36H 03/0600Z 18.2N 133.2W 85 KT 100 MPH
48H 03/1800Z 19.1N 136.5W 80 KT 90 MPH
72H 04/1800Z 20.4N 142.0W 70 KT 80 MPH
96H 05/1800Z 21.4N 146.4W 65 KT 75 MPH
120H 06/1800Z 22.2N 149.6W 60 KT 70 MPH

$$
Forecaster Stewart

[Kingarabian]

The past 4 GFS solutions have been a recurve closer to Hawaii, while the Euro continues to show a comfortable recurve well northeast of Hawaii.

18z GFS shifted a bit north compared to the 12z and 06z runs. More in line with yesterdays 00z run.



Storm is still 6-7days away. Lot's of model error possible. Both the GFS and Euro ensembles have shown a lot of spread.

[Kingarabian]

Looks like half of the 18z GFS ensembles show a track closer or over Hawaii compared to the operational model...

[cycloneye]

Hurricane Norman Discussion Number 20
NWS National Hurricane Center Miami FL EP162018
800 PM PDT Sat Sep 01 2018

Norman looked a little ragged in satellite imagery near 0000 UTC.
Since that time, though, the hurricane looks better organized, with
the eyewall convection better defined in visible and infrared
imagery. Satellite intensity estimates have changed little since
the past advisory, so the initial intensity remains a possibly
generous 90 kt.

The initial motion is now 280/11. The hurricane is expected to be
steered by a strong deep-layer subtropical ridge to the north,
resulting in a generally west-northwestward motion with an increase
in forward speed during the next 2-3 days. After that time, a
decrease in forward speed is expected as Norman approaches a
weakness in the ridge. There is some spread in the guidance at
days 4-5, with the HWRF on the north side of the guidance envelope
showing a northwestward turn and the GFS on the south side showing a
more westward motion. The new forecast track is similar to the
previous track and lies just to the south of the center of the
guidance envelope.

Norman is expected to be in a light shear environment for 48-72 h.
However, during this time the cyclone will be moving over cooler
sea surface temperatures and into a drier air mass. Based on the
guidance, the intensity forecast calls for little change in
strength for 24 h followed by a gradual weakening from 24-72 h.
After 72 h, increasing southerly shear should cause a faster
weakening. It should be noted that there is a chance that Norman
could get stronger than forecast while over warm water during the
next 12-18 h as indicated by the HWRF and HMON models.

FORECAST POSITIONS AND MAX WINDS

INIT 02/0300Z 16.7N 126.0W 90 KT 105 MPH
12H 02/1200Z 17.1N 128.3W 90 KT 105 MPH
24H 03/0000Z 18.0N 131.4W 90 KT 105 MPH
36H 03/1200Z 18.9N 134.7W 85 KT 100 MPH
48H 04/0000Z 19.8N 137.8W 80 KT 90 MPH
72H 05/0000Z 21.0N 143.5W 70 KT 80 MPH
96H 06/0000Z 21.5N 147.5W 60 KT 70 MPH
120H 07/0000Z 23.0N 150.5W 55 KT 65 MPH

$$
Forecaster Beven

[Kingarabian]

Guess who's back

https://i.imgur.com/chW5qX3.gif

[Kingarabian]

Solid 6.0 right now. Think Zelinsky shouldve upped it to a cat.3.



Eye warms a bit more and it'll be close to a 6.5.

[Kingarabian]

II. PACIFIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
2. OUTLOOK FOR SUCCEEDING DAY.....NEGATIVE.
3. ADDITIONAL DAY OUTLOOK: POSSIBLE NOAA G-IV SYNOPTIC
SURVEILLANCE MISSION AROUND HURRICANE NORMAN FOR
05/0000Z DEPARTING PHNL AT 04/1730Z.

[cycloneye]

Hurricane Norman Discussion Number 21
NWS National Hurricane Center Miami FL EP162018
200 AM PDT Sun Sep 02 2018

Norman's structure has continued to slowly improve this morning. A
ragged, but fairly clear, eye has been apparent in shortwave and
longwave IR imagery for the past several hours, and cloud tops
around the eye have generally cooled. The initial intensity has
been held at 90 kt, in agreement with the latest Dvorak fixes from
TAFB and SAB. However, the most recent objective intensity
estimates from the UW-CIMSS ADT are slightly higher, suggesting this
estimate could be conservative.

Given that Norman appears to be on the upswing, the forecast now
allows for some slight re-strengthening over the next 12 h while the
hurricane remains over warm waters and the shear is expected to be
light. Beyond that time, however, there has been no significant
change to the intensity forecast reasoning or the guidance. The
cyclone is still expected to gradually weaken as it encounters a
marginal environment consisting of cool SSTs, fairly dry air, and by
the end of the forecast period, increasing shear. At 24 h and
beyond, the NHC forecast is very close to the intensity consensus,
and has not been substantially changed from the previous advisory.

Norman is beginning to accelerate and the initial motion estimate is
290/11. A strong deep-layer subtropical ridge to the north should
keep Norman moving generally westward to west-northwestward through
most of the forecast period, with a notable increase in speed for
the next day or two. All of the models agree on this general
scenario, however there is still some north-south spread in the
guidance, with the GFS and ECMWF on opposite sides of the guidance
envelope. Like the previous forecast, the official track forecast
generally splits these models and lies near the middle of the
guidance envelope and the consensus aids, FSSE and HCCA.

FORECAST POSITIONS AND MAX WINDS

INIT 02/0900Z 17.1N 127.5W 90 KT 105 MPH
12H 02/1800Z 17.7N 129.8W 95 KT 110 MPH
24H 03/0600Z 18.6N 133.0W 90 KT 105 MPH
36H 03/1800Z 19.4N 136.3W 85 KT 100 MPH
48H 04/0600Z 20.1N 139.7W 80 KT 90 MPH
72H 05/0600Z 20.8N 144.6W 70 KT 80 MPH
96H 06/0600Z 21.5N 149.0W 65 KT 75 MPH
120H 07/0600Z 23.0N 152.0W 60 KT 70 MPH

$$
Forecaster Zelinsky

[xtyphooncyclonex]

Road to Cat 5? (Part 2)

16E NORMAN 180902 1200 17.4N 128.3W EPAC 115 948

[cycloneye]

Hurricane Norman Discussion Number 22
NWS National Hurricane Center Miami FL EP162018
800 AM PDT Sun Sep 02 2018

Norman has made a remarkable and surprising come back today.
Satellite images reveal a distinct eye surrounded by a ring of very
deep convection, and Dvorak T-numbers from both TAFB and SAB reached
T6.0 around 1200 UTC. These numbers have leveled off since then. On
this basis, the initial intensity has been increased to 115 kt,
making Norman again a Category Four Hurricane on the Saffir-Simpson
Scale. The hurricane, however, will begin to approach lower SSTs,
and although some of the intensity models are more aggressive in
forecasting strengthening, the NHC forecast prefers the consensus
IVCN, and forecasts a gradual weakening beyond 12 to 24 hours.

Norman is moving toward the west-northwest at 16 kt. There is a
strong subtropical ridge anchored to the north of Norman, and this
flow pattern will continue to steer the hurricane between the
west and west-northwest at the same speed for the next 2 to 3 days.
By then, the ridge is forecast to be weaker and a turn toward the
northwest is expected by the end of the forecast period. Track
guidance is in very good agreement, and unanimously, all models
forecast the gradual turn to the northwest beyond 4 days. The NHC
track forecast is in the middle of the envelope and is not much
different from the earlier one.

FORECAST POSITIONS AND MAX WINDS

INIT 02/1500Z 17.6N 129.1W 115 KT 130 MPH
12H 03/0000Z 18.2N 131.5W 115 KT 130 MPH
24H 03/1200Z 19.1N 134.7W 100 KT 115 MPH
36H 04/0000Z 20.0N 138.2W 90 KT 105 MPH
48H 04/1200Z 20.5N 141.5W 80 KT 90 MPH
72H 05/1200Z 21.0N 146.0W 70 KT 80 MPH
96H 06/1200Z 22.0N 150.0W 65 KT 75 MPH
120H 07/1200Z 24.0N 153.0W 55 KT 65 MPH

$$
Forecaster Avila