EPAC: FERNANDA - Remnants - Discussion

[Sciencerocks]

[cycloneye]

Hurricane Fernanda Discussion Number 13
NWS National Hurricane Center Miami FL EP072023
1100 AM HST Tue Aug 15 2023

Fernanda seems to be resuming a weakening trend possibly due to
moderate deep-layer shear and embedded dry air. Infrared satellite
images indicate that the coverage of deep convection has decreased
during the past few hours. Subjective Dvorak estimates from SAB and
TAFB remain at 77 kt and 102 kt, respectively. CIMSS ADT and AiDT
estimates are in the 90 kt to 99 kt range. Thus, the initial
intensity is decreased to 90 kt for this advisory.

The hurricane is now moving westward at 10 kt. The track forecast
reasoning remains unchanged. A weak mid-level ridge to the northwest
of Fernanda is expected to steer the cyclone generally westward over
the next several days. The current NHC track forecast has been
updated with minor adjustments.

The official forecast track takes Fernanda over cooler waters,
crossing the 26C isotherm in 18 to 24 hours. While the current
moderate vertical wind shear is expected to diminish in about 12
hours, the hurricane will be encountering an increasingly dry and
stable airmass. Therefore, Fernanda is forecast to quickly weaken
over the next couple of days. Fernanda is now expected to become a
post-tropical cyclone in 48 hours.


FORECAST POSITIONS AND MAX WINDS

INIT 15/2100Z 17.3N 122.8W 90 KT 105 MPH
12H 16/0600Z 17.4N 124.6W 80 KT 90 MPH
24H 16/1800Z 17.6N 127.2W 65 KT 75 MPH
36H 17/0600Z 17.7N 129.9W 50 KT 60 MPH
48H 17/1800Z 17.9N 132.8W 35 KT 40 MPH...POST-TROPICAL
60H 18/0600Z 18.2N 135.8W 30 KT 35 MPH...POST-TROP/REMNT LOW
72H 18/1800Z 18.4N 138.8W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 19/1800Z 18.4N 144.9W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 20/1800Z 18.2N 150.5W 25 KT 30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Delgado/Bucci

[cycloneye]

Hurricane Fernanda Discussion Number 14
NWS National Hurricane Center Miami FL EP072023
500 PM HST Tue Aug 15 2023

Fernanda continues weakening this evening. The overall structure of
the hurricane on visible and infrared satellite has not changed
much, with its central dense overcast remaining mostly intact.
However, recent microwave imagery from GMI and SSMIS show the
inner-core structure has degraded more quickly, with the low- and
mid-level eye signatures no longer aligned, and the deepest
convection becoming increasingly displaced west of the low-level
center. Subjective intensity estimates were both down to T4.5/77 kt
from TAFB and SAB, but some of the objective intensity estimates,
such as UW-CIMSS ADT remain a bit higher, up near 90 kt. The initial
intensity this advisory is set at 80 kt, closer to the lower end of
the intensity guidance range.

Fernanda's inner core is becoming increasingly ragged, likely due to
the unfavorable combination of mid-level shear undercutting its
outflow, very dry mid-level environmental air, and sea-surface
temperatures which are quickly decreasing. These factors foreshadow
weakening, likely rapid, over the next few days, and Fernanda is
expected to become a post-tropical remnant low in about 48 hours.
This forecast is in good agreement with the global and
regional-hurricane model guidance which shows the cyclone losing
organized deep convection around that time frame.

The motion of Fernanda remains just poleward of due west, but a bit
faster than before at 280/12 kt, as the mid-level ridge to its north
has become better established. The track guidance this cycle has
actually shifted a bit south, possibly in response to the storm
quickly weakening in the short-term forecast and becoming more
steered by the low-level trade wind flow. Thus, the latest NHC track
forecast has been shifted a bit to the south of the prior one, but
not quite as far as HCCA and TVCE consensus aids.


FORECAST POSITIONS AND MAX WINDS

INIT 16/0300Z 17.3N 124.1W 80 KT 90 MPH
12H 16/1200Z 17.4N 126.1W 65 KT 75 MPH
24H 17/0000Z 17.5N 128.9W 55 KT 65 MPH
36H 17/1200Z 17.6N 131.7W 40 KT 45 MPH
48H 18/0000Z 17.7N 134.7W 30 KT 35 MPH...POST-TROP/REMNT LOW
60H 18/1200Z 17.9N 137.7W 30 KT 35 MPH...POST-TROP/REMNT LOW
72H 19/0000Z 17.9N 140.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 20/0000Z 18.0N 146.7W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 21/0000Z 18.1N 152.3W 25 KT 30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Papin

[Sciencerocks]

[cycloneye]

Hurricane Fernanda Discussion Number 15
NWS National Hurricane Center Miami FL EP072023
1100 PM HST Tue Aug 15 2023

Fernanda's structure is becoming more ragged and less organized this
evening, as it moves into a drier and more stable airmass. Infrared
satellite trends since the previous advisory have drastically
deteriorated, with convection dissipating, particularly on the
northern side of the system. Cloud tops have been warming over the
last few hours as well. Subjective Dvorak final-T estimates were
lower for this cycle as well with SAB and TAFB at T3.5 and 4.0,
respectively. Although, some of the objective intensity estimates
from UW-CIMSS are still a bit higher. Using a blend of satellite
estimates and assuming a lag in the spin down of Fernanda's winds,
the initial intensity for this advisory is set at 65 kt.

Fernanda continues to weaken, barely holding on to hurricane
strength. Vertical wind shear continues to effect the system, as
well as rapidly cooling sea-surface temperatures, and mid-level
relative humidity levels below 40 percent. This combination will
continue to cause rapid weakening, and Fernanda is expected to
become a tropical storm within very soon, and a post-tropical
cyclone in about 36 h. There is good agreement from global model
simulated infrared satellite images that the cyclone will be void
of deep convection in about 36 h. The remnant low is now expected
to open up into a trough by day 5.

The motion of Fernanda remains generally westward, with a mid-level
ridge expected to continue to steer the cyclone generally westward
throughout the forecast period. The track guidance this cycle once
again shifted a bit south, possibly in response to the storm quickly
weakening and becoming more steered by the low-level flow. Thus,
the latest NHC track forecast has been shifted a bit to the south of
the prior one, but not quite as far as south as the HCCA corrected
consensus.


FORECAST POSITIONS AND MAX WINDS

INIT 16/0900Z 17.4N 125.5W 65 KT 75 MPH
12H 16/1800Z 17.2N 127.5W 55 KT 65 MPH
24H 17/0600Z 17.1N 130.2W 40 KT 45 MPH
36H 17/1800Z 17.2N 132.9W 35 KT 40 MPH...POST-TROPICAL
48H 18/0600Z 17.3N 135.7W 30 KT 35 MPH...POST-TROP/REMNT LOW
60H 18/1800Z 17.5N 138.7W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 19/0600Z 17.7N 141.6W 20 KT 25 MPH...POST-TROP/REMNT LOW
96H 20/0600Z 17.7N 147.6W 20 KT 25 MPH...POST-TROP/REMNT LOW
120H 21/0600Z...DISSIPATED

$$
Forecaster Kelly/Berg

[Sciencerocks]

[cycloneye]

BULLETIN
Tropical Storm Fernanda Advisory Number 16
NWS National Hurricane Center Miami FL EP072023
500 AM HST Wed Aug 16 2023

...FERNANDA NOW A TROPICAL STORM...


SUMMARY OF 500 AM HST...1500 UTC...INFORMATION
----------------------------------------------
LOCATION...17.1N 126.8W
ABOUT 1165 MI...1875 KM WSW OF THE SOUTHERN TIP OF BAJA CALIFORNIA
MAXIMUM SUSTAINED WINDS...65 MPH...100 KM/H
PRESENT MOVEMENT...W OR 260 DEGREES AT 15 MPH...24 KM/H
MINIMUM CENTRAL PRESSURE...994 MB...29.36 INCHES

[wxman57]

It had no convection at 9Z and was still classified as a 65kt hurricane. Looking more like a remnant low now.

[cycloneye]

Tropical Storm Fernanda Discussion Number 17
NWS National Hurricane Center Miami FL EP072023
1100 AM HST Wed Aug 16 2023

Fernanda's weakening trend appears to be continuing. Deep
convection remains minimal, and is confined to a few cells over the
southwestern portion of the circulation while the system moves over
marginal SSTs and into a dry low- to mid-level air mass. There have
been no recent scatterometer overpasses from which to estimate
intensity. Assuming a continued spin down of the circulation, the
advisory intensity is set to a somewhat uncertain 45 kt.

The cyclone has been moving just slightly south of due west or
260/12 kt. A mid-level ridge is forecast to remain established to
the north of Fernanda through 72 hours. This should maintain a
mostly westward track for the next few days. There is little
change to the new official track forecast, which remains close to
the multi-model dynamical consensus.

Sea surface temperatures beneath the cyclone should gradually
decrease and the environmental air mass is expected to become even
drier over the next couple of days. Therefore, continued weakening
is expected which should result in Fernanda degenerating into a
post-tropical cyclone in 12 hours and dissipating within 72 hours.


FORECAST POSITIONS AND MAX WINDS

INIT 16/2100Z 16.8N 127.8W 45 KT 50 MPH
12H 17/0600Z 16.6N 130.0W 35 KT 40 MPH...POST-TROPICAL
24H 17/1800Z 16.6N 132.6W 30 KT 35 MPH...POST-TROP/REMNT LOW
36H 18/0600Z 16.7N 135.3W 25 KT 30 MPH...POST-TROP/REMNT LOW
48H 18/1800Z 16.7N 138.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
60H 19/0600Z 16.7N 140.6W 20 KT 25 MPH...POST-TROP/REMNT LOW
72H 19/1800Z...DISSIPATED

$$
Forecaster Pasch

[Sciencerocks]

[cycloneye]

Tropical Storm Fernanda Discussion Number 18
NWS National Hurricane Center Miami FL EP072023
500 PM HST Wed Aug 16 2023

Fernanda has refused to give in to the increasingly inhibiting
environment and has recently produced a fragmented band with
associated -63 degree Celsius cloud top temperatures in the
west quadrant of the cyclone. Assuming, however, that the
new burst is insufficient to maintain Fernanda's previous advisory
intensity of 45 kt, the initial intensity is lowered to 40 kt.

Cooler oceanic temperatures (sub 26C) and an very dry, stable
marine-layer air mass should result in continued weakening. Fernanda
is expected to degenerate into a post-tropical cyclone in 12 hours,
with dissipation occurring this weekend.

The initial motion is estimated to be just south of due west, or
265/13 kt. There has been no change to the forecast track
philosophy. A subtropical ridge should remain anchored to the north
of Fernanda during the next few days. Accordingly, Fernanda is
forecast to move generally westward through the period. The track
guidance remains tightly clustered, and only a slight along-track
adjustment was needed for the latest NHC forecast.


FORECAST POSITIONS AND MAX WINDS

INIT 17/0300Z 16.7N 129.4W 40 KT 45 MPH
12H 17/1200Z 16.6N 131.4W 35 KT 40 MPH...POST-TROPICAL
24H 18/0000Z 16.5N 134.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
36H 18/1200Z 16.5N 136.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
48H 19/0000Z 16.5N 139.1W 25 KT 30 MPH...POST-TROP/REMNT LOW
60H 19/1200Z 16.5N 141.7W 20 KT 25 MPH...POST-TROP/REMNT LOW
72H 20/0000Z...DISSIPATED

$$
Forecaster Roberts

[Sciencerocks]

[Sciencerocks]

[cycloneye]

Bye.

EP, 07, 2023081712, , BEST, 0, 164N, 1315W, 30, 1005, LO

[cycloneye]

Post-Tropical Cyclone Fernanda Discussion Number 20
NWS National Hurricane Center Miami FL EP072023
500 AM HST Thu Aug 17 2023

Fernanda has lacked convective activity since yesterday evening and
is therefore considered a post-tropical cyclone. With no
convective activity, Dvorak estimates are no longer a reliable
source for intensity guidance. The initial intensity is lowered to
30 kt for this advisory largely based on the trend in geostationary
satellite imagery. An occasional burst of convection is still
possible given 25-26 degrees C sea surface temperatures along the
forecast track of Fernanda. Model guidance indicates the cyclone
will continue to weaken in an increasingly dry and stable
environment for the next few days and is likely to dissipate by
day 3.

The remnant low is moving westward at 13 kt. This general motion
is expected to continue for the next few days as the system is
steered by the low-level flow around a ridge to its north.

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


FORECAST POSITIONS AND MAX WINDS

INIT 17/1500Z 16.4N 132.2W 30 KT 35 MPH...POST-TROPICAL
12H 18/0000Z 16.4N 134.1W 25 KT 30 MPH...POST-TROP/REMNT LOW
24H 18/1200Z 16.4N 136.6W 25 KT 30 MPH...POST-TROP/REMNT LOW
36H 19/0000Z 16.4N 139.2W 25 KT 30 MPH...POST-TROP/REMNT LOW
48H 19/1200Z 16.3N 141.7W 20 KT 25 MPH...POST-TROP/REMNT LOW
60H 20/0000Z 16.4N 144.4W 20 KT 25 MPH...POST-TROP/REMNT LOW
72H 20/1200Z...DISSIPATED

$$
Forecaster Bucci