EPAC: ISELLE - Post-Tropical

[Nancy Smar]

99E.INVEST

[Nancy Smar]

99E INVEST 200825 1200 14.7N 116.7W EPAC -25 1004

[Yellow Evan]

Another low pressure system is located several hundred miles
southwest of the southern tip of the Baja California peninsula.
Although this system is currently producing limited shower and
thunderstorm activity, its circulation has become better defined
during the past several hours. Some additional development of the
disturbance is expected and it will likely become a tropical
depression during the next few days while it moves slowly
east-northeastward to northeastward.
* Formation chance through 48 hours...medium...60 percent.
* Formation chance through 5 days...high...70 percent.

[Yellow Evan]

25/2330 UTC 15.0N 117.2W T1.0/1.0 99E -- East Pacific

[Yellow Evan]

Another low pressure system is located about 700 miles southwest of
the southern tip of the Baja California peninsula. Showers and
thunderstorms are showing some signs of organization, and this
system will likely become a tropical depression during the next
day or two while it moves slowly east-northeastward to
northeastward.
* Formation chance through 48 hours...high...80 percent.
* Formation chance through 5 days...high...90 percent.

[Yellow Evan]

26/0530 UTC 15.4N 117.5W T1.0/1.0 99E -- East Pacific

[Yellow Evan]

Showers and thunderstorms associated with an area of low pressure
located about 700 miles southwest of the southern tip of the Baja
California peninsula have become better organized overnight and
recent satellite derived wind data show that the surface circulation
has become better defined. If these development trends continue,
advisories will be initiated later this morning. The system is
forecast to move slowly east-northeastward to northeastward over the
open eastern Pacific.
* Formation chance through 48 hours...high...90 percent.
* Formation chance through 5 days...high...90 percent.

[Yellow Evan]

26/1130 UTC 15.0N 117.6W T1.5/1.5 99E -- East Pacific

[cycloneye]

Tropical Depression Fourteen-E Discussion Number 1
NWS National Hurricane Center Miami FL EP142020
800 AM PDT Wed Aug 26 2020

Earlier scatterometer data and GOES-16 Proxy-VIS satellite
imagery indicate that the area of low pressure located several
hundred miles southwest of the southern tip of the Baja California
peninsula has acquired sufficient convective organization and a
well-defined surface circulation, and is now classified as a
tropical cyclone. Dvorak satellite intensity estimates and the
aforementioned scatterometer data support an initial wind speed
of 30 kt for this advisory.

Moderate to strong east-northeasterly shear, the same inhibiting
upper wind pattern that is affecting depression Thirteen-E, is
forecast to hamper significant development through the entire
forecast period. Therefore, only modest strengthening in the
next 24 hours is expected, which agrees with the statistical-
dynamical guidance and the large-scale models.

The depression is moving rather slowly toward the northeast, or
040/2 kt. The low to mid-level steering synoptic pattern consists
of a cyclonic gyre stretching southwestward from Hurricane Laura
over central Mexico and into the eastern Pacific. This feature
should cause the depression to continue in a northeastward general
direction at a relatively slow pace through Friday. Afterward, a
gradual turn toward the north-northwest and west-northwest is
expected as high pressure currently over the southwestern U.S.
builds westward over the Baja California peninsula and adjacent
eastern Pacific. The NHC official forecast is a reflection of a
blend of the HCCA and TVCE consensus aids.

FORECAST POSITIONS AND MAX WINDS

INIT 26/1500Z 15.4N 117.2W 30 KT 35 MPH
12H 27/0000Z 15.8N 116.9W 30 KT 35 MPH
24H 27/1200Z 16.4N 116.4W 35 KT 40 MPH
36H 28/0000Z 17.0N 115.7W 35 KT 40 MPH
48H 28/1200Z 17.8N 114.9W 35 KT 40 MPH
60H 29/0000Z 18.6N 114.1W 30 KT 35 MPH
72H 29/1200Z 19.6N 113.5W 30 KT 35 MPH
96H 30/1200Z 21.4N 114.3W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 31/1200Z 22.4N 116.1W 25 KT 30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Roberts

[galaxy401]

Both Depressions are forecast to only be minimal TS at best. The shear from Laura is probably going to inhibit them.

[aspen]

Both Depressions are forecast to only be minimal TS at best. The shear from Laura is probably going to inhibit them.

Shear from Genevieve was originally suspected to be an issue for the developing Laura. Now it gets to return the favor.

[Yellow Evan]

26/1720 UTC 15.1N 116.7W T2.0/2.0 14E -- East Pacific

[Extratropical94]

And another one

Tropical Storm Iselle Discussion Number 2
NWS National Hurricane Center Miami FL EP142020
200 PM PDT Wed Aug 26 2020

A recent ASCAT overpass revealed that the cyclone barely has a
closed center, and is embedded in a northeast-southwest oriented
monsoon gyre feature. However, this same overpass sampled a
decent sized area of 33-34 kt winds over the southeastern quadrant,
and therefore the system has been upgraded to 35 kt Tropical Storm
Iselle.

Assuming that the storm does not get absorbed into the monsoon gyre
and open back into a trough, it should maintain its intensity over
warm waters, while battling 20-30 kt of easterly to northeasterly
shear over the next few days. After that time, the shear persists
but Iselle should begin to move over waters with a lower oceanic
heat content. This should cause the cyclone to weaken and eventually
degenerate into a remnant low late in the forecast period. The
latest NHC intensity forecast is near the various intensity
consensus guidance.

The depression is moving northeast at 4 kt. This motion is expected
to continue for the next day or so as it moves around the cyclonic
gyre stretching southwestward from Hurricane Laura over central
Mexico and into the eastern Pacific. Afterward, a gradual turn
toward the north-northwest and west-northwest is expected as high
pressure currently over the southwestern U.S. builds westward over
the Baja California peninsula and adjacent eastern Pacific. The NHC
forecast track is little changed from the previous one, and lies
near the HFIP corrected consensus, or HCCA.


FORECAST POSITIONS AND MAX WINDS

INIT 26/2100Z 15.5N 116.8W 35 KT 40 MPH
12H 27/0600Z 16.0N 116.3W 35 KT 40 MPH
24H 27/1800Z 16.8N 115.7W 35 KT 40 MPH
36H 28/0600Z 17.3N 115.1W 35 KT 40 MPH
48H 28/1800Z 17.9N 114.4W 35 KT 40 MPH
60H 29/0600Z 18.7N 113.7W 35 KT 40 MPH
72H 29/1800Z 19.9N 113.7W 30 KT 35 MPH
96H 30/1800Z 21.4N 114.9W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 31/1800Z 22.1N 116.1W 25 KT 30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Latto

[Kingarabian]

EPAC going gangbusters

[aspen]

EPAC going gangbusters

It’s attempting to stay relevant now that Laura has taken the spotlight. It’s failing miserably.

[Yellow Evan]

EPAC going gangbusters

If you mean producing minimal tropical storms by gangbusters, sure.

[Kingarabian]

EPAC going gangbusters

It’s attempting to stay relevant now that Laura has taken the spotlight. It’s failing miserably.

It's a cool-neutral entering La Nina year. I'm not trippin'. We already saw a long tracker and a major near the Mexican coast.

[wx98]

These are both gonna be in nearly the same spot by Saturday. Wonder if we finally see some Fujiwhara?

[Yellow Evan]

0
WTPZ44 KNHC 270258
TCDEP4

Tropical Storm Iselle Discussion Number 3
NWS National Hurricane Center Miami FL EP142020
800 PM PDT Wed Aug 26 2020

Satellite imagery indicates that a convective burst has formed a
little closer to the center of Iselle during the past few hours,
although the circulation remains at least somewhat elongated.
Various subjective and objective satellite intensity estimates are
near 35 kt, so that remains the initial intensity. The imagery, as
well as model analyses, show that Iselle continues to be undergoing
strong easterly shear.

Iselle is embedded in a large monsoon gyre, and the southwesterly
flow on the south side of the gyre should be the main steering
influence for the next 60 h or so. This should result in the
cyclone continuing its current slow motion toward the northeast.
After that time, the cyclone should separate from the gyre, allowing
a mid-level ridge to the north and northeast of the system to become
the dominant steering mechanism. This should cause Iselle to turn
to the north, then northwest, then eventually to the west. The
track guidance is in good agreement with the general scenario,
although there is some spread on when and where there turns will
occur. The new forecast track is close to the HCCA corrected
consensus mode and has only minor adjustments from the previous
forecast.

Present indications are that the current strong shear will persist
for several days, and after 72 h the forecast track takes the
cyclone over cooler sea surface temperatures. Based on this,
significant strengthening appears unlikely, although short-lived
spin ups due to convective bursts are possible. The new intensity
forecast is unchanged from the previous forecast in showing little
change of strength for 72 h, followed by weakening to a depression
and a remnant low. An alternative scenario is that the shear causes
Iselle to weaken to a trough at any time during the next 120 h.


FORECAST POSITIONS AND MAX WINDS

INIT 27/0300Z 16.2N 116.2W 35 KT 40 MPH
12H 27/1200Z 16.7N 115.8W 35 KT 40 MPH
24H 28/0000Z 17.3N 115.3W 35 KT 40 MPH
36H 28/1200Z 17.9N 114.7W 35 KT 40 MPH
48H 29/0000Z 18.6N 114.1W 35 KT 40 MPH
60H 29/1200Z 19.4N 113.6W 35 KT 40 MPH
72H 30/0000Z 20.7N 113.7W 30 KT 35 MPH
96H 31/0000Z 22.5N 115.5W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 01/0000Z 22.5N 116.5W 25 KT 30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Beven

[Kingarabian]

Wow has it been 6 years already since Iselle 2014? Man time flys.