EPAC: OLAF - Post-Tropical

[Yellow Evan]

Close but not classifiable.

[Sciencerocks]

[Yellow Evan]

15E FIFTEEN-E 210907 1800 18.1N 107.8W EPAC 30 1007

[cycloneye]

Tropical Depression Fifteen-E Discussion Number 1
NWS National Hurricane Center Miami FL EP152021
300 PM MDT Tue Sep 07 2021

Over the past day or so, convection has gradually become better
organized in association with the area of low pressure offshore
of the coast of southwestern Mexico. There is now a large curved
band to the east of the center, and outflow is increasing in all
quadrants. Based on the improving convective organization,
advisories are being initiated on Tropical Depression Fifteen-E. An
ASCAT-B overpass a few hours ago indicated the peak winds associated
with the depression were 26 kt, and assuming some undersampling, the
initial advisory intensity is set at 30 kt.

The depression has been moving slowly west-northwestward today, to
the south of a weak mid-level ridge over northwestern Mexico.
Another ridge is forecast to begin building from the southwestern
United States to over northern Mexico tonight, which should turn the
cyclone to the northwest. The system should then gradually
accelerate through midweek as it gets caught in the flow between
this ridge, and a mid- to upper-level trough to its west. By late in
the forecast period, a turn to the west is expected as the cyclone
weakens and becomes steered by the low-level flow. The model
guidance is generally in good agreement on this scenario, and the
NHC track forecast is close to the various model consensus
solutions. It should be noted that based on this track forecast,
the center of the cyclone would approach within 120 n mi of the
southern tip of the Baja California peninsula on Thursday.
Therefore, any deviation in the track to the right would increase
the chance for impacts to that area.

There are very favorable environmental conditions around the
depression that should allow for strengthening over the next couple
of days. The only inhibiting factor for quick strengthening in the
short term appears to be the lack of a tight circulation and
inner-core convection. Because of this, the NHC intensity forecast
is on the lower end of the guidance through the first 24 hours,
nearest to the LGEM, as it appears the HWRF/HMON are a bit too
aggressive in intensifying the cyclone during that time. By 24
hours, it is assumed that the inner-core will become better
established, and faster strengthening is indicated from 24 to 48
hours. By 72 hours, the system is forecast to begin moving over
much cooler waters and into a dry, stable atmospheric environment,
which should cause weakening. By this weekend, the cyclone is
expected to degenerate into a remnant low. The NHC intensity
forecast beyond 24 hours is very near the IVCN consensus.


FORECAST POSITIONS AND MAX WINDS

INIT 07/2100Z 18.2N 107.9W 30 KT 35 MPH
12H 08/0600Z 18.4N 108.1W 35 KT 40 MPH
24H 08/1800Z 19.0N 108.6W 45 KT 50 MPH
36H 09/0600Z 20.0N 109.3W 55 KT 65 MPH
48H 09/1800Z 21.1N 110.5W 65 KT 75 MPH
60H 10/0600Z 22.4N 112.0W 65 KT 75 MPH
72H 10/1800Z 23.4N 113.7W 55 KT 65 MPH
96H 11/1800Z 24.5N 116.5W 40 KT 45 MPH
120H 12/1800Z 24.5N 118.9W 30 KT 35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Latto

[Kingarabian]

Yeah low end hurricane probably its ceiling.

[Yellow Evan]

Given the structure of the storm, I wouldn’t expect much development until about 24-36 hours from now. By then, it won’t have much time until it moves over the steep gradient of the California Current. I don’t think it’ll become a hurricane.

[Kingarabian]

Given the structure of the storm, I wouldn’t expect much development until about 24-36 hours from now. By then, it won’t have much time until it moves over the steep gradient of the California Current. I don’t think it’ll become a hurricane.

This is pretty reasonable.

[Yellow Evan]

TXPZ26 KNES 072354
TCSENP

A. 15E (NONAME)

B. 07/2330Z

C. 18.5N

D. 106.8W

E. FIVE/GOES-W

F. T2.0/2.5

G. IR/EIR/VIS

H. REMARKS...CIRCULAR TIGHTLY DEFINED CLOUD LINES AROUND A LLCC THAT IS
UNDER A SMALL CLOUD OVERCAST MAKES THE DT EQUAL TO 2.0 USING THE SHEAR
PATTERN. THE MET AND PT AGREE WITH THE DT BASED ON A DEVELOPMENT TREND
OVER THE PAST 24 HOURS. THE FT IS BASED ON THE MET DUE TO UNCERTAINTY
WITH THE EXACT LLCC POSITION IN RECENT SATELLITE IMAGERY.

I. ADDL POSITIONS

NIL


...SAMBUCCI

[Yellow Evan]

15E FIFTEEN 210908 0000 18.1N 107.3W EPAC 30 1007

[Yellow Evan]

18z GFS increases the threat to Baja California Sur.

[Sciencerocks]

[Netzero9455]

Getting tired of all this rain. We got like 30 inches of rain last month here in Puerto Vallarta, and we're almost at twice the normal rainfall level year-to-date. I thought precipitation was generally elevated during El Nino years, and since this is a cool neutral tending towards La Nina, why is there so much rain for the coast of Jalisco? So many tropical disturbances brushing past us this year. Is there a general pattern that keeps disturbances closer to the coast for some reason?

[Yellow Evan]

577
WTPZ45 KNHC 080243
TCDEP5

Tropical Depression Fifteen-E Discussion Number 2
NWS National Hurricane Center Miami FL EP152021
900 PM MDT Tue Sep 07 2021

Satellite imagery indicates that Tropical Depression Fifteen-E has
changed little in organization during the past several hours.
While the system is producing good convective banding in the
eastern semicircle, the convection near the center is currently
poorly organized, and there is no evidence that the inner core has
consolidated. Thus, the initial intensity remains 30 kt based
mainly on continuity from the previous advisory. A combination of
conventional and 37 GHz microwave satellite imagery suggests that
the center is farther east than previously thought, so the new
initial position is about a half degree east of the previous
advisory position.

The initial motion is a somewhat uncertain 300/5. A large mid-level
anticyclone is located over the southwestern United States with a
ridge extending southeastward across Mexico. The anticyclone
should shift a little eastward during the next few days, with the
ridge extending southward across Mexico. This evolution should
steer the tropical cyclone generally northwestward for the next
several days, followed by a more westward motion as the cyclone
weakens over cooler water and is steered by low-level easterly flow.
The track guidance is in good agreement with this scenario, and the
new forecast track is near the consensus models. However, the
more eastward initial position required an eastward shift to the
forecast track. It should be noted that some erratic motion is
possible until the cyclone develops a better-defined inner core.

Conditions appear favorable for strengthening until the system
reaches the 26-deg-C SST isotherm in 60-72 h, with the main
restraining factor being the current lack of internal organization.
The intensity forecast has only minor adjustments from the previous
forecast and calls for the depression to become a tropical storm in
about 12 h and a hurricane in about 48 h. Steady to rapid weakening
is expected after 60-72 h due to the cooler water and dry air
entrainment.

The more easterly initial position and the new forecast track
require a Tropical Storm Watch for portions of Baja California Sur
at this time. Interests elsewhere in Baja California Sur should
monitor the progress of this system.


FORECAST POSITIONS AND MAX WINDS

INIT 08/0300Z 18.2N 107.4W 30 KT 35 MPH
12H 08/1200Z 18.6N 107.7W 35 KT 40 MPH
24H 09/0000Z 19.4N 108.4W 45 KT 50 MPH
36H 09/1200Z 20.4N 109.2W 55 KT 65 MPH
48H 10/0000Z 21.7N 110.6W 65 KT 75 MPH
60H 10/1200Z 22.8N 112.0W 65 KT 75 MPH
72H 11/0000Z 23.7N 113.7W 55 KT 65 MPH
96H 12/0000Z 24.5N 116.5W 40 KT 45 MPH
120H 13/0000Z 24.0N 119.0W 25 KT 30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Beven

[Yellow Evan]

TXPZ26 KNES 080558
TCSENP

A. 15E (NONAME)

B. 08/0530Z

C. 18.7N

D. 106.9W

E. FIVE/GOES-W

F. T2.0/2.5

G. IR/EIR/SWIR

H. REMARKS...CIRCULAR TIGHTLY DEFINED CLOUD LINES AROUND A LLCC THAT
IS LESS THAN 1.25 DEGREES FROM A LARGE COLD OVERCAST MAKES THE DT EQUAL
TO 2.0 USING THE SHEAR PATTERN. THE MET AND PT AGREE WITH THE DT BASED
ON A DEVELOPMENT TREND OVER THE PAST 24 HOURS. THE FT IS BASED ON THE
MET DUE TO UNCERTAINTY WITH THE EXACT LLCC POSITION.

I. ADDL POSITIONS

NIL


...SAMBUCCI

[Kingarabian]

Getting tired of all this rain. We got like 30 inches of rain last month here in Puerto Vallarta, and we're almost at twice the normal rainfall level year-to-date. I thought precipitation was generally elevated during El Nino years, and since this is a cool neutral tending towards La Nina, why is there so much rain for the coast of Jalisco? So many tropical disturbances brushing past us this year. Is there a general pattern that keeps disturbances closer to the coast for some reason?

Steering is favored closer to Mexico this season due to a persistently weaker ridge just off the SWUSA and northern Mexico.

[cycloneye]

Tropical Depression Fifteen-E Discussion Number 3
NWS National Hurricane Center Miami FL EP152021
300 AM MDT Wed Sep 08 2021

The circulation of the depression has continued to become better
defined, and there has been a substantial increase in deep
convection within bands to the north and northeast of the center.
However, the inner core remains slightly displaced from this
activity, and a combination of subjective and objective intensity
estimates supports maintaining the cyclone as a 30-kt depression
for this advisory.

The system has either been meandering or its center re-formed
yesterday, and the long-term motion is a drift toward the
north-northwest (335 degrees) at about 3 kt. This motion is likely
due to the depression being caught within weak steering currents
between a mid-level low west of the Baja California peninsula and
troughing extending across Mexico to the Gulf of Mexico. A strong
mid-tropospheric high over the western United States should
gradually cause the system to move faster toward the northwest
during the next 2 to 3 days, bringing it very close to Baja
California Sur in about 48 hours. Of the track models, the GFS and
COAMPS-TC models are the solutions which bring the cyclone's center
closest to Baja California Sur, while the ECMWF and UKMET models
have the farther-offshore tracks. The new NHC track forecast
splits the difference among these solutions and is a little east
of the previous forecast during the first 36 hours to account for
recent short-term motions. After 36 hours, it falls more or less
in line with the previous prediction and is very close to the
consensus aids, HWRF, and HMON.

There are counteracting factors at play regarding the depression's
future intensity. Although deep-layer shear is forecast to be low,
the GFS suggests that moderate to strong mid-level shear could
develop below the outflow level during the next 24-48 hours. Sea
surface temperatures will be plenty warm for strengthening during
the next 48 hours, yet upper-level divergence is not expected to be
ideal. Since the system's circulation appears to be improving,
steady strengthening is forecast during the first 48 hours, and the
depression could become a short-lived hurricane while it passes the
Baja California peninsula. This forecast is near the upper end
of the guidance envelope, close to the GFS, HWRF, COAMPS-TC, and
HCCA solutions. The cyclone will be moving over colder waters in
2-3 days, which should cause quick weakening and a degeneration to
remnant low status by day 4.


Key Messages:

1. Tropical Depression Fifteen-E is expected to strengthen to a
tropical storm later today, and it could become a short-lived
hurricane while it passes just to the southwest of southern
portions of Baja California Sur Thursday and Friday. A Tropical
Storm Watch is in effect for southern portions of Baja California
Sur, and interests there should continue to monitor the progress of
the depression.

2. Heavy rains associated with Tropical Depression Fifteen-E are
possible across southern portions of Baja California Sur Thursday
through Friday. This will pose a threat of flash flooding and
mudslides.


FORECAST POSITIONS AND MAX WINDS

INIT 08/0900Z 18.5N 107.1W 30 KT 35 MPH
12H 08/1800Z 19.1N 107.6W 40 KT 45 MPH
24H 09/0600Z 20.0N 108.4W 50 KT 60 MPH
36H 09/1800Z 21.1N 109.6W 60 KT 70 MPH
48H 10/0600Z 22.3N 111.2W 65 KT 75 MPH
60H 10/1800Z 23.3N 112.8W 55 KT 65 MPH
72H 11/0600Z 23.9N 114.5W 45 KT 50 MPH
96H 12/0600Z 24.1N 117.1W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 13/0600Z 23.6N 119.6W 25 KT 30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Berg

[Subtrop]

15E OLAF 210908 1200 18.7N 107.3W EPAC 35 1005

[Yellow Evan]

TXPZ26 KNES 081324
TCSENP
CCA

A. 15E (NONAME)

B. 08/1130Z

C. 18.7N

D. 107.1W

E. THREE/GOES-W

F. T3.0/3.0

G. IR/EIR/SWIR

H. REMARKS...CORRECTED FOR INTENSITY BASED ON 1135Z SSMIS MW PASS. SYSTEM
HAS 6/10 BANDING ON 1135Z SSMIS 91 GHZ MW PASS RESULTING IN A DT OF
3.0. THE CONVECTION IS WRAPPING AROUND THE NORTHERN SIDE OF THE LLCC ON
EIR IMAGERY. THE 24 HR TREND IS DEVELOPING. MET AND PT ARE 3.0. FT IS
BASED ON DT.

I. ADDL POSITIONS

NIL


...PATEL

[cycloneye]

Tropical Storm Olaf Discussion Number 4
NWS National Hurricane Center Miami FL EP152021
900 AM MDT Wed Sep 08 2021

The depression has strengthened into Tropical Storm Olaf this
morning. A well-defined curved band now wraps over 50 percent around
the center of the cyclone, with cloud tops to -80 degrees C. The
initial intensity has been raised to 35 kt for this advisory based
on the latest TAFB Dvorak intensity estimate and the UW-CIMSS ADT.

Olaf is forecast to remain over warm waters and in a moist
environment for the next 36 hours or so. The only inhibiting factor
to strengthening in the short term could be a slight increase in
vertical wind shear beginning tonight. In a couple of days, the
cyclone is forecast to begin moving over cooler waters and into a
drier, much more stable atmospheric environment that favors rapid
weakening. These unfavorable conditions should cause Olaf to
degenerate into a remnant low this weekend. The latest NHC intensity
forecast was decreased only slightly from the previous one, and is
in good agreement with the IVCN intensity consensus. Although the
NHC forecast no longer explicitly shows Olaf becoming a hurricane,
this could still occur Thursday or Thursday night.

The storm is now moving northwestward at 6 kt, to the southwest of a
mid-level ridge building over northern Mexico. This northwestward
motion should continue for a couple of days with a gradual increase
in forward speed. By Friday night, Olaf is expected to turn
west-northwestward as it weakens, and by Saturday a westward motion
is forecast as the cyclone becomes shallow and steered by the
surrounding low-level flow. The latest NHC track forecast is little
changed from the previous one, and lies near the various multi-model
consensus tracks. It should be noted that the model solutions that
depict a stronger cyclone favor a track slightly more to the north
than the NHC forecast, closer to the southern Baja peninsula, while
the weaker model solutions lie to the south of the NHC forecast
track.

Key Messages:

1. Olaf is forecast to strengthen to near hurricane intensity
while it passes to the southwest of southern portions of Baja
California Sur Thursday and Friday, and tropical storm conditions
are possible in these areas. Interests there should continue to
monitor the progress of Olaf.

2. Heavy rains associated with Olaf are possible across southern
portions of Baja California Sur Thursday through Friday. This will
pose a threat of flash flooding and mudslides.

FORECAST POSITIONS AND MAX WINDS

INIT 08/1500Z 18.9N 107.5W 35 KT 40 MPH
12H 09/0000Z 19.6N 108.0W 45 KT 50 MPH
24H 09/1200Z 20.6N 109.0W 55 KT 65 MPH
36H 10/0000Z 21.7N 110.5W 60 KT 70 MPH
48H 10/1200Z 22.9N 112.2W 55 KT 65 MPH
60H 11/0000Z 23.5N 113.9W 45 KT 50 MPH
72H 11/1200Z 23.8N 115.4W 35 KT 40 MPH
96H 12/1200Z 23.7N 118.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 13/1200Z 23.0N 120.7W 25 KT 30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Latto

[Sciencerocks]