EPAC: HENRIETTE - Post-Tropical - Discussion

[cycloneye]

Tropical Storm Henriette Discussion Number 11
NWS National Hurricane Center Miami FL EP082025
1100 AM HST Wed Aug 06 2025

Henriette continues along with little change in its structure. Like
6 h ago, it is producing a relatively small area of deep convection,
with cold cloud tops present mostly to the north of its low-level
center. Recent scatterometer data showed winds just above 40 kt,
which supports maintaining the intensity at 45 kt for this
advisory, after accounting for undersampling. The scatterometer data
was also helpful with identifying the exact position of Henriette's
center, which was slightly south of previous estimates.

No significant change was made to the NHC track forecast outside a
slight southward adjustment based on the initial position estimate
in the short term. Henriette is moving westward to
west-northwestward to the south of a deep ridge centered over the
northern east Pacific. In a few days, a trough approaching from the
west will turn Henriette toward the northwest, taking the tropical
cyclone north of Hawaii. The various deterministic and global
ensemble models are all in good agreement on the forecast, so
confidence in the track forecast is fairly high.

The tropical storm is still forecast to slowly weaken during the
next few days while it moves over cool SSTs near 24C. However, once
Henriette moves north of Hawaii, it will move over warmer waters.
Upper-level difluent flow associated with a mid-latitude trough to
the northwest may also provide additional support for
intensification. As a result, most of the dynamical models forecast
strengthening to occur near the end of the forecast period, and the
NHC intensity forecast reflects this and is very similar to the
previous advisory.

FORECAST POSITIONS AND MAX WINDS

INIT 06/2100Z 18.1N 131.3W 45 KT 50 MPH
12H 07/0600Z 18.3N 133.5W 45 KT 50 MPH
24H 07/1800Z 18.6N 136.5W 40 KT 45 MPH
36H 08/0600Z 19.0N 139.5W 40 KT 45 MPH
48H 08/1800Z 19.7N 142.5W 40 KT 45 MPH
60H 09/0600Z 20.7N 145.2W 40 KT 45 MPH
72H 09/1800Z 22.0N 147.8W 40 KT 45 MPH
96H 10/1800Z 24.9N 152.0W 50 KT 60 MPH
120H 11/1800Z 28.5N 156.0W 60 KT 70 MPH

$$
Forecaster Santos/D. Zelinsky

[Kingarabian]

Models seeing a strong weakness NW of the Hawaiian Islands that pulls this NW. Looks like no WPAC crosser or any Hawaii threat.

[cycloneye]

EP, 08, 2025080700, , BEST, 0, 181N, 1317W, 45, 1004, TS

[Yellow Evan]

GFS last 2 runs have backed off re-intensification.

[cycloneye]

Tropical Storm Henriette Discussion Number 12
NWS National Hurricane Center Miami FL EP082025
500 PM HST Wed Aug 06 2025

Henriette’s satellite presentation has deteriorated since the
previous advisory, with the cyclone now nearly devoid of all deep
convection and the low-level center fully exposed. The most recent
subjective Dvorak intensity estimates were 3.0/45 kt from TAFB,
while SAB deemed the cyclone too weak to classify. Meanwhile,
objective estimates from UW-CIMSS have ranged from 37 to 51 kt over
the past several hours. An earlier 06/1755Z Metop-C ASCAT pass
depicted numerous 40 kt wind barbs, with a single 40–45 kt wind barb
noted north of the low-level center. Based on these data, the
initial intensity for this advisory is maintained, at perhaps a
generous, 45 kt.

The cyclone is moving westward, or 275 degrees, at 14 kt. This
general motion is expected to persist tonight and Thursday, as
Henriette continues to be steered by a strengthening subtropical
ridge to its north. A gradual turn toward the west-northwest and
eventually northwest is expected to begin Friday and continue
through the weekend, as an amplifying longwave trough northwest of
Hawaii begins to erode the western extent of the subtropical ridge.
The official track forecast remains closely aligned with the latest
multi-model consensus aids and is largely unchanged from the
previous advisory. There is high confidence that the center of
Henriette will remain far to the north of the Hawaiian Islands.

Henriette will be moving over gradually cooling sea surface
temperatures, lowering to near 24C, while mid-level relative
humidity also falls below 50 percent. Despite these marginal
thermodynamic conditions, Henriette’s well-established circulation
is likely to remain resilient due to the low-shear environment the
cyclone will be transiting through. As a result, only slight
weakening is forecast during the next 12 hours or so, followed by
little change in strength through 72 hours. If Henriette can
survive the passage over the cooler waters, as has been advertised
by the GFS and ECMWF models for several days now, re-intensification
appears likely over the weekend and into early next week as sea
surface temperatures warm to levels conducive for strengthening.
The official intensity forecast reflects this, bringing Henriette to
hurricane strength by 120 hours. The intensity forecast is mostly
unchanged and remains closely aligned with the dynamical intensity
guidance aid HCCA and the regional hurricane models.


FORECAST POSITIONS AND MAX WINDS

INIT 07/0300Z 18.2N 132.4W 45 KT 50 MPH
12H 07/1200Z 18.3N 134.8W 40 KT 45 MPH
24H 08/0000Z 18.7N 137.9W 40 KT 45 MPH
36H 08/1200Z 19.2N 141.0W 40 KT 45 MPH
48H 09/0000Z 20.0N 143.8W 40 KT 45 MPH
60H 09/1200Z 21.1N 146.4W 40 KT 45 MPH
72H 10/0000Z 22.5N 149.0W 45 KT 50 MPH
96H 11/0000Z 25.5N 153.3W 55 KT 65 MPH
120H 12/0000Z 29.0N 157.5W 65 KT 75 MPH

$$
Forecaster Jelsema (CPHC)

[cycloneye]

Tropical Storm Henriette Discussion Number 13
NWS National Hurricane Center Miami FL EP082025
1100 PM HST Wed Aug 06 2025

Satellite images indicate that a small burst of deep convection has
developed just to the northwest of Henriette’s low-level center this
evening, after several hours with not much more than a shallow cloud
swirl. The most recent subjective Dvorak current intensity estimate
from TAFB was 3.0/45 kt, while the objective estimates from UW-CIMSS
ranged between 32 to 42 kt over the past several hours. A timely
07/0645Z Metop-C ASCAT pass depicted several 40 kt wind barbs, with
a single 40–45 kt wind barb noted north of the low-level center.
The initial intensity for this advisory will be held at 45 kt,
utilizing the ASCAT data while accounting for some undersampling and
a known low bias at higher speeds.

The cyclone is moving westward, or 275 degrees, at 14 kt. This
general motion is expected to persist through Thursday, as Henriette
continues to be steered by a strengthening subtropical ridge to its
north. A gradual turn toward the west-northwest and eventually
northwest is anticipated Friday and over the weekend, as an
amplifying longwave trough northwest of Hawaii begins to erode the
western extent of the subtropical ridge. The northwestward motion is
expected to continue into early next week. The official track
forecast remains closely aligned with the latest multi-model
consensus aids and is nearly identical to the previous advisory.

Henriette will be moving over gradually cooling sea surface
temperatures near 24C, while the environmental humidities
surrounding the cyclone will drop below 50 percent. Despite these
hostile thermodynamic conditions, Henriette’s well-established
circulation is likely to remain resilient due to the low-shear
environment the cyclone will be transiting through. As a result,
only a slight weakening is forecast tonight, followed by little
change in strength during the next few days. If Henriette can
survive the passage over the cool waters, as persistently suggested
by the GFS and ECMWF models for several days now, re-intensification
appears likely over the weekend and into early next week as sea
surface temperatures warm to levels conducive for strengthening.
The official forecast continues to reflect this, bringing Henriette
to hurricane strength by 120 hours. The intensity forecast is
mostly unchanged and remains aligned best with the dynamical
intensity consensus aid HCCA and the regional hurricane models.


FORECAST POSITIONS AND MAX WINDS

INIT 07/0900Z 18.4N 133.9W 40 KT 45 MPH
12H 07/1800Z 18.6N 136.2W 40 KT 45 MPH
24H 08/0600Z 19.1N 139.3W 40 KT 45 MPH
36H 08/1800Z 19.8N 142.3W 40 KT 45 MPH
48H 09/0600Z 20.7N 145.1W 40 KT 45 MPH
60H 09/1800Z 21.9N 147.7W 40 KT 45 MPH
72H 10/0600Z 23.3N 150.1W 45 KT 50 MPH
96H 11/0600Z 26.9N 154.8W 55 KT 65 MPH
120H 12/0600Z 30.2N 158.9W 65 KT 75 MPH

$$
Forecaster Jelsema (CPHC)

[cycloneye]

Tropical Storm Henriette Discussion Number 14
NWS National Hurricane Center Miami FL EP082025
500 AM HST Thu Aug 07 2025

Henriette continues to hang in there despite straddling 25 C
sea-surface temperatures. Since the prior advisory, a little more
convection has redeveloped close to the estimated center, though
overall the appearance of the tropical storm is still rather ragged
looking. The current intensity estimate from TAFB has not changed
for 12 UTC at 45 kt. In deference to this value and earlier
scatterometer data, the initial intensity is being maintained at 45
kt this advisory.

The tropical storm continues to move westward, or 280 degrees at 14
kt. This general motion will continue through today, followed by a
turn west-northwestward and then more northwestward due to the
influence of a subtropical ridge to its north that will become
gradually eroded by a large mid-oceanic trough amplifying over the
North-Central Pacific in 2-3 days. The track guidance is essentially
a carbon copy of the previous cycle, and only slight changes were
made to the official track forecast. This forecast lies near the
various multi-model consensus aids.

Henriette is already moving over cool ocean waters, which are
expected to cool to 24C over the next 12-24 hours. While it would
not be surprising to see a little more weakening over the short
term, the storm has proven to be resilient thus far. Another
environmental factor to consider is the upper-level temperatures,
which are colder than normal due to a negatively tilted upper-level
trough to the storm's west. This trough might help to sustain some
convection over what would ordinarily be waters too cool to allow
such activity to persist. Once Henriette begins to move over warmer
ocean waters again in the Central Pacific west of 150W, the other
environmental factors are expected to remain favorable, and
intensification is shown in the latter half of the forecast period.
In fact, Henriette could become a hurricane in 96-120 h well to the
north of Hawaii. The latest NHC intensity forecast is a little
higher than the prior advisory, though there remain some guidance
aids that are even higher than the NHC forecast at the end of the
period (HAFS-B).


FORECAST POSITIONS AND MAX WINDS

INIT 07/1500Z 18.6N 135.5W 45 KT 50 MPH
12H 08/0000Z 19.0N 137.9W 45 KT 50 MPH
24H 08/1200Z 19.5N 140.9W 45 KT 50 MPH
36H 09/0000Z 20.2N 143.8W 45 KT 50 MPH
48H 09/1200Z 21.4N 146.5W 45 KT 50 MPH
60H 10/0000Z 22.7N 148.9W 45 KT 50 MPH
72H 10/1200Z 24.3N 151.4W 50 KT 60 MPH
96H 11/1200Z 28.0N 155.8W 65 KT 75 MPH
120H 12/1200Z 31.5N 160.0W 70 KT 80 MPH

$$
Forecaster Papin

[Kingarabian]

NHC forecasting this to become a hurricane well North of Hawaii.

[cycloneye]

NHC forecasting this to become a hurricane well North of Hawaii.

Do you know how many times it has occured? I guess not many.

[Hurricanehink]

NHC forecasting this to become a hurricane well North of Hawaii.

Do you know how many times it has occured? I guess not many.

Check out Hurricane Hiki in 1950, which was a hurricane just north of Hawaii. https://en.wikipedia.org/wiki/Hurricane_Hiki

Or in 1975, when a hurricane was closer to Alaska than Hawaii! https://en.wikipedia.org/wiki/1975_Pacific_hurricane_season#Unnamed_hurricane

[cycloneye]

Tropical Storm Henriette Discussion Number 15
NWS National Hurricane Center Miami FL EP082025
1100 AM HST Thu Aug 07 2025

Henriette has been producing a smaller area of deep convection than
earlier, as it seems to be struggling a bit with dry air and
sea-surface temperatures near 24 C. The latest subjective Dvorak
current intensity estimates are 2.5/35 kt from TAFB and 1.5/25 kt
from SAB. The latest objective estimates from UW-CIMMS range from
about 30 to 40 kt. A recent 1914 UTC ASCAT-C pass suggests that
Henriette has likely weakened a bit from earlier. Based on the
above data, the initial intensity is lowered to 40 kt for this
advisory.

The motion of 280/14 kt is unchanged from the previous advisory.
This motion will continue through today as Henriette is steered by
mid-level ridging well to its north. The cyclone will then round
the southwestern periphery of the mid-level ridge as a large
deep-layer trough approaches from the west. These features will
cause Henriette to gradually turn toward the northwest in a couple
of days. Very little change has been made to the NHC track
forecast, which lies near the tightly clustered consensus aids.
Confidence in the track forecast is high through the weekend, and
Henriette will not directly impact the Hawaiian Islands.

Henriette is expected to continue moving over cool ocean waters near
24C for another 36 h before it begins to gradually move over
increasing water temperatures. The tropical storm will also
continue moving through a very dry environment. Most of the
guidance shows the storm maintaining a 35-40 kt intensity during
this time. Henriette is also expected to encounter colder than
normal mid- and upper-level temperatures in a couple of days. If
Henriette survives the next 48 h or so, then strengthening would
appear likely later in the forecast period due to increasing
sea-surface temperatures, very low vertical wind shear, and
decreasing mid- to upper-level temperatures as the aforementioned
deep-layer trough approaches. The official forecast shows some
slight weakening in the short term, followed by strengthening to a
hurricane by day 4 well to the north of Hawaii. The latest NHC
forecast is near the intensity consensus and close to the higher end
of the guidance at day 4 and 5. It should be noted that the HAFS
models are showing a slightly higher intensity than the NHC
forecast.


FORECAST POSITIONS AND MAX WINDS

INIT 07/2100Z 18.9N 136.8W 40 KT 45 MPH
12H 08/0600Z 19.3N 139.2W 40 KT 45 MPH
24H 08/1800Z 19.9N 142.2W 40 KT 45 MPH
36H 09/0600Z 20.9N 145.0W 40 KT 45 MPH
48H 09/1800Z 22.1N 147.5W 40 KT 45 MPH
60H 10/0600Z 23.5N 150.0W 45 KT 50 MPH
72H 10/1800Z 25.2N 152.3W 55 KT 65 MPH
96H 11/1800Z 28.9N 156.7W 70 KT 80 MPH
120H 12/1800Z 32.6N 160.6W 65 KT 75 MPH

$$
Forecaster Hagen

[Kingarabian]

NHC forecasting this to become a hurricane well North of Hawaii.

Do you know how many times it has occured? I guess not many.

Check out Hurricane Hiki in 1950, which was a hurricane just north of Hawaii. https://en.wikipedia.org/wiki/Hurricane_Hiki

Or in 1975, when a hurricane was closer to Alaska than Hawaii! https://en.wikipedia.org/wiki/1975_Pacific_hurricane_season#Unnamed_hurricane

That 1975 track is impressive. Let's see if Henriette will do something similar. Hurricane Hikis track has been common in the 90s and 2000s.

[cycloneye]

Tropical Storm Henriette Discussion Number 16
NWS National Hurricane Center Miami FL EP082025
500 PM HST Thu Aug 07 2025

Henriette’s satellite presentation has changed little since the
previous advisory, with the low-level center remaining mostly
exposed and only a few small, intermittent bursts of deep convection
developing near the low-level center. The latest subjective Dvorak
intensity estimate from TAFB was 2.5/35 kt, while objective
estimates from UW-CIMSS have ranged from 28 to 41 kt over the past
several hours. Taking a blend of these data, the initial intensity
has been reduced to 35 kt for this advisory.

Henriette is moving westward, or 280 degrees at 14 kt. A turn
toward the west-northwest is expected tonight, with this general
motion expected to persist over the next couple of days as the
cyclone tracks along the southwestern periphery of a subtropical
ridge to its north. A turn toward the northwest is forecast this
weekend and into early next week as Henriette becomes
steered between an amplifying longwave trough northwest of Hawaii
and the subtropical ridge to its northeast. The official track
forecast remains in close agreement with the latest multi-model
consensus aids and is essentially unchanged from the previous
advisory. Confidence remains high that Henriette will remain far
to the north of Hawaii.

Henriette will traverse sea surface temperatures near 24C with
mid-level relative humidity below 50 percent during the next 24 to
36 hours. Despite these unfavorable thermodynamic conditions, the
cyclone’s well-defined circulation is expected to remain fairly
resilient within the prevailing low-shear environment, allowing for
occasional pulses of deep convection to persist. As a result,
little change in intensity is anticipated in the short term. If
Henriette can withstand the period over cooler waters, as has been
consistently indicated by the GFS and ECMWF models for several days
now, re-intensification will likely occur over the weekend and into
early next week as sea surface temperatures rise to levels conducive
for strengthening. The official forecast continues to reflect
intensification, bringing Henriette to hurricane strength by 96
hours. The intensity forecast is on the higher end of the guidance
envelope, and is most closely aligned with the dynamical intensity
consensus HCCA.


FORECAST POSITIONS AND MAX WINDS

INIT 08/0300Z 19.1N 138.4W 35 KT 40 MPH
12H 08/1200Z 19.6N 140.8W 35 KT 40 MPH
24H 09/0000Z 20.4N 143.8W 35 KT 40 MPH
36H 09/1200Z 21.6N 146.5W 35 KT 40 MPH
48H 10/0000Z 22.9N 149.0W 40 KT 45 MPH
60H 10/1200Z 24.4N 151.3W 50 KT 60 MPH
72H 11/0000Z 26.2N 153.6W 60 KT 70 MPH
96H 12/0000Z 30.2N 157.7W 70 KT 80 MPH
120H 13/0000Z 34.8N 161.8W 65 KT 75 MPH

$$
Forecaster Jelsema (CPHC)

[cycloneye]

Last advisory from NHC.

BULLETIN
Tropical Storm Henriette Advisory Number 17
NWS National Hurricane Center Miami FL EP082025
1100 PM HST Thu Aug 07 2025

...HENRIETTE ENTERS THE CENTRAL PACIFIC BASIN...


SUMMARY OF 1100 PM HST...0900 UTC...INFORMATION
-----------------------------------------------
LOCATION...19.2N 140.1W
ABOUT 975 MI...1570 KM E OF HILO HAWAII
MAXIMUM SUSTAINED WINDS...40 MPH...65 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 17 MPH...28 KM/H
MINIMUM CENTRAL PRESSURE...1008 MB...29.77 INCHES

[StormWeather]

If Henriette degrades to a remnant low, the NHC plans to maintain advisories on it due to the high chance that it will regenerate

ZCZC HFOTCDCP3 ALL
TTAA00 PHFO DDHHMM

Tropical Storm Henriette Discussion Number 18
NWS Central Pacific Hurricane Center Honolulu HI EP082025
Issued by NWS National Hurricane Center Miami FL
500 AM HST Fri Aug 08 2025

Henriette has failed to produce deep convection for about 12 hours
now. The latest subjective Dvorak estimates are 25 kt from JTWC and
too weak to classify from SAB and PHFO. Recent objective intensity
estimates range from 25 to 40 kt. An earlier ASCAT pass from 0535
UTC showed a large area of 30-33 kt vectors on the north side of
Henriette. Henriette will be maintained as a 35-kt tropical storm
for this advisory, but it could degenerate to a post-tropical
remnant low at any time today.

The cyclone is moving just north of due west at 280/15 kt. A turn to
the west-northwest is expected soon as the cyclone tracks along the
southwestern periphery of a subtropical ridge to its northeast. A
turn toward the northwest is forecast late this weekend into early
next week as Henriette becomes steered between an amplifying
longwave trough northwest of Hawaii and the subtropical ridge to its
northeast. The NHC track forecast is nearly identical to the
previous one and is in good agreement with the tightly clustered
consensus aids. Confidence remains high that Henriette will remain
far to the north of Hawaii.

Henriette is over 24C sea-surface temperatures (SSTs) and is
embedded within a dry airmass. These cold SSTs are expected to
persist along the cyclone's track for another 12 to 24 h. If
Henriette doesn't generate organized convection soon, it could
degenerate to a remnant low today, and this is explicitly shown in
the NHC forecast Beyond 24 h, Henriette (or its remnants) will
encounter progressively warmer water temperatures over the weekend,
peaking around 26-27C in about 3 days. Upper-level temperatures are
also expected to decrease in a couple of days as the aforementioned
trough approaches Henriette, which would increase instability. These
factors, along with relatively low shear, will likely allow
Henriette to restrengthen later this weekend into early next week,
as depicted by most of the models. The NHC intensity forecast is at
the low end of the guidance envelope through 36 h, and at the high
end of the guidance at 72-96 h. Beyond day 4, wind shear from the
longwave trough and cooling SSTs should lead to steady weakening as
Henriette moves farther into the mid-latitudes.

Even if Henriette becomes post-tropical today, given the high
likelihood of regeneration back into a tropical cyclone and
subsequent restrengthening, NHC plans on maintaining advisories
during the post-tropical phase.


FORECAST POSITIONS AND MAX WINDS

INIT 08/1500Z 19.7N 141.5W 35 KT 40 MPH
12H 09/0000Z 20.3N 143.7W 30 KT 35 MPH...POST-TROP/REMNT LOW
24H 09/1200Z 21.3N 146.3W 30 KT 35 MPH...POST-TROP/REMNT LOW
36H 10/0000Z 22.6N 148.7W 35 KT 40 MPH...TROPICAL CYCLONE
48H 10/1200Z 24.1N 150.9W 45 KT 50 MPH
60H 11/0000Z 25.9N 153.2W 55 KT 65 MPH
72H 11/1200Z 27.9N 155.7W 65 KT 75 MPH
96H 12/1200Z 32.3N 160.4W 65 KT 75 MPH
120H 13/1200Z 37.1N 165.1W 50 KT 60 MPH

$$
Forecaster Hagen

NNNN

[cycloneye]

Post-Tropical Cyclone Henriette Discussion Number 19
NWS Central Pacific Hurricane Center Honolulu HI EP082025
Issued by NWS National Hurricane Center Miami FL
1100 AM HST Fri Aug 08 2025

Approximately 18 hours have passed since Henriette last produced any
significant areas of deep convection, and the cyclone has now been
downgraded to a post-tropical remnant low. The current motion is
now west-northwestward, or 285/15 kt. There are no changes to the
track forecast philosophy. Henriette will move west-northwestward
along the southwestern periphery of a subtropical ridge to its
northeast. A turn toward the northwest is forecast late this
weekend into early next week as Henriette becomes steered between an
amplifying longwave trough northwest of Hawaii and the subtropical
ridge to its northeast. No significant changes were made to the NHC
track forecast, which is near the middle of the guidance envelope.
Confidence remains high that Henriette will remain far to the north
of Hawaii.

The cyclone is currently over 24C sea-surface temperatures (SSTs)
and located within a very dry environment. Over the next couple of
days, Henriette will enter an area of gradually increasing SSTs. At
the same time, an approaching longwave trough will bring colder
temperatures aloft near Henriette, which will increase the
instability. The majority of the model guidance indicates this will
be enough to reignite convection and cause Henriette to restrengthen
to a tropical storm. The peak intensity forecast in about 72 hours
has been lowered slightly from the previous NHC forecast, and now
lies between the middle and upper end of the guidance. Beyond day
4, wind shear from the longwave trough and cooling SSTs should lead
to steady weakening as Henriette moves farther into the
mid-latitudes.

Given the high likelihood of regeneration back into a tropical
cyclone and subsequent restrengthening, NHC will be maintaining
advisories during the post-tropical phase.


FORECAST POSITIONS AND MAX WINDS

INIT 08/2100Z 19.9N 143.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
12H 09/0600Z 20.7N 145.1W 30 KT 35 MPH...POST-TROP/REMNT LOW
24H 09/1800Z 21.9N 147.5W 30 KT 35 MPH...POST-TROP/REMNT LOW
36H 10/0600Z 23.3N 149.8W 40 KT 45 MPH...TROPICAL CYCLONE
48H 10/1800Z 25.0N 152.0W 50 KT 60 MPH
60H 11/0600Z 26.9N 154.3W 55 KT 65 MPH
72H 11/1800Z 29.1N 156.9W 60 KT 70 MPH
96H 12/1800Z 33.5N 161.5W 55 KT 65 MPH
120H 13/1800Z 39.0N 165.9W 45 KT 50 MPH

$$
Forecaster Hagen

Post-Tropical Cyclone Henriette Discussion Number 20
NWS Central Pacific Hurricane Center Honolulu HI EP082025
Issued by NWS National Hurricane Center Miami FL
500 PM HST Fri Aug 08 2025

Henriette remains a post-tropical remnant low, consisting of a
well-defined low-level swirl with a recent burst of deep convection
that has persisted north of the center for the past few hours. This
convective pulse has not persisted long enough, nor organized
sufficiently, to justify reclassifying the system as a tropical
cyclone at this time. Given the marginal environment and a recent
ASCAT pass, the initial intensity is held at 30 kt for this
advisory.

The remnant low is moving west-northwestward at 290/14 kt, steered
by a low- to mid-level ridge to its north. This general motion is
expected to continue through tonight. From 24 to 72 hours, Henriette
should gradually turn toward the northwest as it approaches a
weakness in the ridge caused by an amplifying upper-level trough
well northwest of Hawaii. Between 72 and 96 hours, the system is
forecast to turn toward the north-northwest as the trough becomes
the primary steering feature. The updated track forecast is very
similar to the previous advisory and lies close to the consensus
aids, which remain tightly clustered through the forecast period.

The system is currently located over sea-surface temperatures near
24 degrees C and within a stable, dry mid- to upper-level
environment, which should limit convective coverage in the short
term. However, global model guidance continues to indicate that the
system will traverse a tongue of slightly warmer waters over the
weekend. At the same time, increasing upper-level divergence
associated with the approaching trough should enhance instability
and favor the redevelopment of persistent deep convection. This is
expected to allow the system to regenerate into a tropical cyclone
over the weekend, with gradual strengthening into early next week.
Model phase-space diagrams indicate it will likely maintain a
shallow warm-core structure during its peak. Thereafter, increasing
shear and diminishing outflow should support a transition to steady
weakening as it becomes absorbed into the mid-latitudes. The new
intensity forecast is very similar to the previous NHC forecast and
lies near the middle- to upper-end of the guidance envelope.


FORECAST POSITIONS AND MAX WINDS

INIT 09/0300Z 20.2N 144.6W 30 KT 35 MPH...POST-TROP/REMNT LOW
12H 09/1200Z 21.1N 146.4W 30 KT 35 MPH...POST-TROP/REMNT LOW
24H 10/0000Z 22.3N 148.7W 35 KT 40 MPH...TROPICAL CYCLONE
36H 10/1200Z 23.9N 151.0W 40 KT 45 MPH
48H 11/0000Z 25.8N 153.2W 50 KT 60 MPH
60H 11/1200Z 27.8N 155.6W 55 KT 65 MPH
72H 12/0000Z 29.9N 158.1W 55 KT 65 MPH
96H 13/0000Z 34.5N 162.6W 50 KT 60 MPH
120H 14/0000Z 39.7N 166.1W 40 KT 45 MPH

$$
Forecaster Gibbs (CPHC)

[cycloneye]

Tropical Depression Henriette Discussion Number 21
NWS Central Pacific Hurricane Center Honolulu HI EP082025
Issued by NWS National Hurricane Center Miami FL
1100 PM HST Fri Aug 08 2025

Deep convection that developed north of Henriette’s well-defined
low-level circulation earlier today has persisted during the past
several hours. Given this sustained convective activity and the
presence of a closed surface circulation, Henriette is being
reclassified as a tropical depression. A Metop-B ASCAT pass at 0655
UTC indicated peak winds up to 30 kt in the northern semicircle,
supporting the initial intensity estimate of 30 kt.

The initial motion is toward the west-northwest at about 13 kt,
steered by a low- to mid-level ridge to its north. This general
motion is expected to continue through the next 24 hours. From 24 to
72 hours, the cyclone should gradually turn toward the northwest as
it approaches a weakness in the ridge caused by an amplifying
upper-level trough well northwest of Hawaii. Between 72 and 96
hours, Henriette is forecast to turn toward the north-northwest as
the trough becomes the primary steering feature. The updated track
forecast remains very similar to the previous advisory and is near
the middle of the tightly clustered consensus aids.

The system is currently located over sea surface temperatures near
24 degrees C and within a stable, dry mid- to upper-level
environment, which should limit convective coverage in the near
term. However, global model guidance indicates that the cyclone will
traverse an area of slightly warmer water between 24 and 72 hours.
At the same time, upper-level divergence is forecast to increase in
association with the approaching trough, which should enhance
instability and support gradual strengthening beginning late
Saturday and continuing into early next week. After that time,
upper-level divergence is forecast to diminish, vertical shear will
increase, and water temperatures will cool sharply. This loss of
outflow support and more hostile environment should result in steady
weakening, with Henriette expected to become a post-tropical remnant
low by 120 h and dissipate soon thereafter as it is absorbed by a
larger mid-latitude system. The new intensity forecast is nearly
unchanged from the previous NHC forecast and lies near the middle-
to upper-end of the guidance envelope.


FORECAST POSITIONS AND MAX WINDS

INIT 09/0900Z 20.7N 145.7W 30 KT 35 MPH
12H 09/1800Z 21.6N 147.4W 30 KT 35 MPH
24H 10/0600Z 23.0N 149.6W 35 KT 40 MPH
36H 10/1800Z 24.8N 151.6W 45 KT 50 MPH
48H 11/0600Z 26.8N 154.2W 50 KT 60 MPH
60H 11/1800Z 28.7N 156.7W 55 KT 65 MPH
72H 12/0600Z 30.8N 159.2W 55 KT 65 MPH
96H 13/0600Z 35.2N 163.7W 45 KT 50 MPH
120H 14/0600Z 39.0N 167.0W 30 KT 35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Gibbs (CPHC)

[cycloneye]

Tropical Depression Henriette Discussion Number 22
NWS Central Pacific Hurricane Center Honolulu HI EP082025
Issued by NWS National Hurricane Center Miami FL
500 AM HST Sat Aug 09 2025

Convection has persisted and perhaps increased slightly in areal
coverage and organization over the last 6 hours. A recent AMSR2
microwave pass paints a similar picture to the GOES-18 imagery, with
the convection confined to the northwest quadrant and the center
located near the edge of the convection. The latest subjective
Dvorak classifications are 1.5/25 kt from JTWC and PHFO, and 1.0
from SAB. The UW-CIMSS objective intensity estimates are higher
than the subjective estimates, mostly in the 30-35 kt range. An
earlier ASCAT-B pass from 0655 UTC indicates that peak winds were at
least 30 kt. The initial intensity is held at 30 kt for this
advisory, but Henriette is close to regaining tropical storm
strength.

The initial motion is toward the west-northwest, or 300 degrees at
12 kt. The global models show that Henriette will round the
southwestern periphery of the subtropical ridge tonight, which will
cause the cyclone to turn toward the northwest, in between the ridge
and an approaching large deep-layer trough to the west. In a couple
days, the trough will become stationary or even retrograde westward.
This steering pattern favors a continued northwestward motion
through the forecast period. The NHC track forecast is very similar
to the previous one and lies near the middle of the tightly
clustered consensus aids.

Henriette will move over gradually warming sea-surface temperatures
(SSTs) and through gradually cooling upper-level temperatures now
through the next 72 h. SSTs currently near 24.5 to 25C are forecast
to warm to the 26.5 to 27C range along the cyclone's path. There is
some uncertainty as to how the expected moderate wind shear may
affect the cyclone, especially given how dry the mid-troposphere
will continue to be along Henriette's path. The shear direction
could be close to the direction of the cyclone's motion, so the
shear shouldn't be as much of a negative factor as the dry air.
Given all the competing factors mentioned above, slow strengthening
seems likely over the next few days. The latest NHC intensity
forecast is similar to the previous one and is near the middle of
the guidance envelope. Beyond day 3, wind shear should increase,
and Henriette will likely reach cooler water again by day 4. These
factors should cause the system to lose its convection and become
post-tropical in 4 to 5 days.


FORECAST POSITIONS AND MAX WINDS

INIT 09/1500Z 21.4N 146.8W 30 KT 35 MPH
12H 10/0000Z 22.3N 148.5W 35 KT 40 MPH
24H 10/1200Z 23.9N 150.6W 40 KT 45 MPH
36H 11/0000Z 25.8N 152.8W 45 KT 50 MPH
48H 11/1200Z 27.9N 155.3W 50 KT 60 MPH
60H 12/0000Z 29.9N 157.9W 55 KT 65 MPH
72H 12/1200Z 32.0N 160.4W 55 KT 65 MPH
96H 13/1200Z 36.1N 165.0W 40 KT 45 MPH
120H 14/1200Z 40.3N 168.5W 25 KT 30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Hagen

[cycloneye]

Tropical Storm Henriette Discussion Number 23
NWS Central Pacific Hurricane Center Honolulu HI EP082025
Issued by NWS National Hurricane Center Miami FL
1100 AM HST Sat Aug 09 2025

Deep convection has evolved a bit since the previous advisory with
a curved band wrapping around the west side of Henriette. The
latest subjective Dvorak classifications range from 25-30 kt, and
the objective intensity estimates from UW-CIMSS have been ranging
between 35-37 kt. Based mainly on the objective estimates, it is
estimated that Henriette has regained tropical storm strength with
maximum winds estimated at 35 kt.

Henriette is moving a little faster now in a direction between
west-northwest and northwest, at 14 kt. Henriette will round the
southwestern periphery of the subtropical ridge tonight as a
deep-layer mid-latitude trough approaches from the west. In a
couple of days, the trough will become stationary or even retrograde
westward. This steering pattern favors a continued northwestward
motion through the forecast period. The new NHC track forecast is a
little faster than the previous one, but along a similar track line,
and is in agreement with the consensus aids.

Henriette will move over gradually warming sea-surface temperatures
(SSTs) and through gradually cooling upper-level temperatures now
through the next 60 h or so. SSTs currently near 25C are forecast
to warm to the 26.5 to 27C range along the cyclone's path. The
cyclone is also currently embedded in very dry mid-tropospheric
air, and these dry conditions are expected to persist for the next
couple of days. Given the competing factors mentioned above, slow
strengthening seems likely over the next couple of days. The
latest NHC intensity forecast is similar to the previous one and is
near the middle of the guidance envelope. Beyond day 3, wind shear
should increase, and Henriette will also reach cooler water again
as it gains latitude. These factors should cause the system to
lose its convection and become post-tropical by day 4, with
dissipation in about 5 days.


FORECAST POSITIONS AND MAX WINDS

INIT 09/2100Z 22.3N 148.1W 35 KT 40 MPH
12H 10/0600Z 23.3N 149.8W 40 KT 45 MPH
24H 10/1800Z 25.1N 151.9W 45 KT 50 MPH
36H 11/0600Z 27.2N 154.3W 50 KT 60 MPH
48H 11/1800Z 29.3N 156.9W 55 KT 65 MPH
60H 12/0600Z 31.4N 159.5W 55 KT 65 MPH
72H 12/1800Z 33.5N 162.0W 50 KT 60 MPH
96H 13/1800Z 37.7N 166.2W 35 KT 40 MPH...POST-TROPICAL
120H 14/1800Z...DISSIPATED

$$
Forecaster Hagen

[cycloneye]

Tropical Storm Henriette Discussion Number 24
NWS Central Pacific Hurricane Center Honolulu HI EP082025
Issued by NWS National Hurricane Center Miami FL
500 PM HST Sat Aug 09 2025

Satellite imagery shows that Henriette's curved band of convection
on the west side of the circulation has fragmented with warming tops
in recent hours, though some redevelopment has begun near and
northwest of the center more recently. An AMSR2 pass at 2130 UTC
confirmed a well-organized low-level structure, and a 2012 UTC
ASCAT-C pass showed peak winds of about 35 kt, consistent with
objective estimates from UW-CIMSS. The initial intensity is held at
35 kt for this advisory.

The initial motion is northwest at 12 kt, steered by a subtropical
ridge to the northeast and an amplifying mid-latitude trough to the
northwest. This motion should persist through early next week,
keeping Henriette well northeast of the Hawaiian Islands. Guidance
indicates the sharp upper trough will cut off into an upper low on
Monday and retrograde westward, a pattern that should maintain
Henriette’s northwestward motion. The updated forecast is very
similar to the previous one and lies near the middle of the tightly
clustered consensus aids.

Sea-surface temperatures along the forecast track should gradually
warm from near 25 C to around 26–27 C through 60 h. Despite the
presence of dry mid- to upper-level air, a combination of warmer
waters and increasing upper-level divergence associated with an
upper trough to the northwest should enhance outflow and support
gradual strengthening. The NHC forecast continues to show a peak
near 55 kt in the 48–60 h period, nearly identical to the previous
forecast and near the middle of the guidance envelope. Thereafter,
cooler waters, increasing shear, and diminishing upper-level outflow
should result in steady weakening, with Henriette expected to become
a post-tropical remnant low by 96 h and dissipate by 120 h as it is
absorbed into the mid-latitude flow.


FORECAST POSITIONS AND MAX WINDS

INIT 10/0300Z 23.0N 149.1W 35 KT 40 MPH
12H 10/1200Z 24.2N 150.7W 40 KT 45 MPH
24H 11/0000Z 26.2N 152.9W 45 KT 50 MPH
36H 11/1200Z 28.3N 155.4W 50 KT 60 MPH
48H 12/0000Z 30.5N 158.1W 55 KT 65 MPH
60H 12/1200Z 32.7N 160.6W 55 KT 65 MPH
72H 13/0000Z 34.9N 163.0W 50 KT 60 MPH
96H 14/0000Z 38.8N 166.9W 35 KT 40 MPH...POST-TROPICAL
120H 15/0000Z...DISSIPATED

$$
Forecaster Gibbs (CPHC)