August 2020:

[srainhoutx]

Tropical Depression Fourteen Discussion Number 2
NWS National Hurricane Center Miami FL AL142020
500 PM EDT Thu Aug 20 2020

An Air Force Reserve Hurricane Hunter aircraft investigating the
system found an area of lighter winds--likely where the center would
be--farther south than previous estimates. The highest flight-level
wind measured by the aircraft was 30 kt at an altitude of 2500 feet,
and although there were some SFMR measurements over 40 kt, these
looked coincident with some heavy rain rates and thus are probably
not reliable. Therefore, the initial intensity remains 30 kt.
Structurally, the depression has a large cloud envelope with
sporadic convective cells located in loose bands.

The updated initial position derived from the aircraft data
indicates that the current motion is still westward, or 270/16 kt.
This southward adjustment really only affected the first 36 hours
or so of the forecast, with NHC's official track forecast being
shifted southward during that period. This ends up taking the
cyclone's center over extreme northern Nicaragua and northeastern
Honduras in 12-24 hours. After 36 hours, model guidance remains in
good agreement that the system should turn northwestward due to a
deep-layer trough over the Gulf of Mexico. The new set of model
guidance has not shifted much from the previous cycle, and the NHC
track forecast is very close to the morning forecast despite the
initial position adjustment, with perhaps a slight eastward shift
on days 4 and 5. In general, the NHC forecast is closest to the
GFS and HCCA model solutions.

The depression's farther-south position makes the intensity
forecast more complicated with potentially more land interaction
with parts of Central America. Slight strengthening to tropical
storm strength is expected before the center reaches Honduras and
Nicaragua, with little change thereafter until the center
re-emerges over the Gulf of Honduras. Low shear and warm sea
surface temperatures should then support further intensification up
until it reaches the Yucatan Peninsula. Since there is significant
uncertainty in how land interaction will affect the cyclone's
intensity, the forecast intensity has been flat-lined between day 2
and day 4, with the understanding that the the winds could increase
or decrease from the value shown. Vertical shear is expected to
increase by day 5, and some weakening is shown at that time.

Key Messages:

1. Tropical Depression Fourteen is expected to strengthen over the
northwestern Caribbean Sea through Saturday, and is likely to
produce tropical-storm-force winds and heavy rainfall over portions
of the coasts of Nicaragua and Honduras, including the Bay Islands,
beginning tonight through Friday. The system could be near or at
hurricane strength when it reaches the Yucatan Peninsula of Mexico
late Saturday, and watches could be required for a portion of that
area tonight.

2. The system is expected to move into the south-central Gulf
of Mexico as a tropical storm on Sunday. Some strengthening is
anticipated while it moves northwestward over the western Gulf of
Mexico early next week, but it is too soon to know exactly how
strong it will get or the location and magnitude of impacts it
will produce along the central or northwestern Gulf Coast.
Interests in that area should continue monitoring the progress of
this system over the next few days.

FORECAST POSITIONS AND MAX WINDS

INIT 20/2100Z 14.3N 81.0W 30 KT 35 MPH
12H 21/0600Z 14.7N 83.0W 35 KT 40 MPH
24H 21/1800Z 15.6N 84.7W 35 KT 40 MPH...INLAND
36H 22/0600Z 17.0N 85.6W 45 KT 50 MPH...OVER WATER
48H 22/1800Z 18.7N 86.6W 55 KT 65 MPH
60H 23/0600Z 20.3N 87.9W 55 KT 65 MPH...INLAND
72H 23/1800Z 22.1N 89.2W 55 KT 65 MPH...OVER WATER
96H 24/1800Z 26.0N 91.5W 55 KT 65 MPH
120H 25/1800Z 28.5N 93.5W 50 KT 60 MPH

$$
Forecaster Berg

[Kingwood36]

Is there a chance it misses the trof?

[Rip76]

Huge storm down near Sargent. Wish I was getting some of that rain

And just sitting there too.

[AtascocitaWX]

so with this still being a TD and no defined center , this could miss the trof ?

[Scott747]

18z ICON has 14 missing the trof while 13 comes through the fla straits. Setting up for the rare potential fujiwhara effect....

[snowman65]

What happens if it misses the trough?

[Scott747]

Depends on the interaction with the 13 which would definitely make a forecast more complicated than normal.

Could easily just wash out and little impacts here. No question the potential outcome is more highly uncertain than usual.

[don]

Early 0z Tropical models have already shifted back west fwiw.I wonder if its due to the center relocation to the south... 18z GFS also shifted west to the Port Arthur area

[Stormlover2020]

Gfs upper Texas coast

[Scott747]

18z GFS with a shift back to the w as a moderate TS.

[Rip76]

I’ll take a moderate TS into Matagorda.

[Scott747]

Early 0z Tropical models have already shifted back west fwiw.I wonder if its due to the center relocation to the south... 18z GFS also shifted west to the Port Arthur area

That really isn't 0z guidance but 18z guidance based on the 12z runs. Could be extrapolated with the further southern placement.

0z guidance based on the 18z runs won't be out till closer to 8-9.

[Cpv17]

I’ll take a moderate TS into Matagorda.

Me and you both. As long as it doesn’t stall that would be nice.

[don]

Early 0z Tropical models have already shifted back west fwiw.I wonder if its due to the center relocation to the south... 18z GFS also shifted west to the Port Arthur area

That really isn't 0z guidance but 18z guidance based on the 12z runs. Could be extrapolated with the further southern placement.

0z guidance based on the 18z runs won't be out till closer to 8-9.

Yeah I was confused about that because the map still states 18z but the model tracks are different than the 18z map from earlier. And it seemed too early to get updated models that soon.But what you said makes since that it could be a updated extrapolation based on the center relocation.

[tireman4]

An interesting set of days coming up. Very fluid situation

[DoctorMu]

18z GFS with a shift back to the w as a moderate TS.

Yep - I'Ding the initial conditions is everything.

[Scott747]

Gotta love the HWRF. 18z brings a convection free td 14 towards Sargent while simultaneously bringing td 13 as a major towards Gulfport/New Orleans.

[DoctorMu]

Gotta love the HWRF. 18z brings a convection free td 14 towards Sargent while simultaneously bringing td 13 as a major towards Gulfport/New Orleans.

Not surprised, but we have a ways still to go. Wild swings in the models may not be over.

Hopefully, both systems remain weak, because prep time could be a lot shorter than ideal, particularly with a pandemic.

[Texaspirate11]

So strange to see 2 storms in the GOM - but it is 2020
It would even be horrific if 14 goes to La and 13 La/Ms border
that would be a real nigthmare iMHO

[Rip76]

Linder PM

Tropical depression moving west over the western Caribbean Sea

Interests along the US Gulf coast of TX and LA should closely monitor the progress of this system

Discussion:
USAF mission this afternoon found a poorly defined and very weak low level circulation well south of what has been depicted on satellite images as the low level center…which in fact is the mid level center. The weak low level center is about 60 miles south of the mid level center and the plane had a difficult time closing off a west wind. While the system looks impressive on satellite images, this can many times be deceptive, and when you pull back the layers and look at the surface this is very close to an open wave axis. With that said, convection has increased today and banding features as well as upper level outflow are increasing.

Track:
TD 14 is moving toward the west at 17mph and is starting to slow as the system reaches the western Caribbean Sea as expected. This motion should continue for the next 24-36 hours followed by a turn toward the NW in response to a large scale trough over the western Gulf of Mexico. Additionally, a large sub-tropical ridge over the Atlantic is building westward and this feature will begin to weaken and eventually lift the trough over the western Gulf toward the north. The timing of this along with the forward motion of the tropical system along with the intensity of the system will all play an important role in the eventual final outcome and landfall along the Gulf coast. Additionally, the system will interact with the landmass of the Yucatan and this will likely result in some disruption of the low level center over the weekend and it is unclear in what shape of where this center enters the Gulf of Mexico on Sunday morning.

Model guidance has trended a bit eastward today from the overnight runs, but some of the more recent 18Z guidance has again shifted back toward the west. The HMON hurricane model as well as the CMC are along the eastern side of the large guidance envelop with the ECWMF and GFS toward the western side. The global guidance ensemble members are spread from NE MX to southern Louisiana. The official NHC forecast track has changed little since this morning with a tropical storm located over the NW Gulf of Mexico by early Tuesday morning.

Intensity:
Conditions in the near term…up to landfall along the Yucatan appear favorable for intensification if/when a well defined low level center forms and an inner core can consolidate. After that, land interact with the Yucatan should result in some weakening, but how much and in what shape the system emerges into the Gulf of Mexico is unclear. Once in the Gulf of Mexico, significant wind shear will be in place over the NW Gulf as the large scale upper level trough begins to lift out to the north, but this shear will be weakening late in the weekend and into early next week. Across TX a large mass of dry air that is currently in place will continue and some of this dry air may become entangled into the circulation. It should be noted that 500-700mb RH in the mid levels decreases from near 70% at 18 hours to around 55% at 108 hours on the SHIPS intensity forecast. SHIPS is also showing some 25-30kts of SSW/SW wind shear over the system as it reaches the NW Gulf of Mexico, but wind shear forecasts are notoriously bad many times in models.

The official NHC forecast brings the depression to a strong tropical storm before landfall on the Yucatan and then maintains a moderate tropical storm across the Gulf of Mexico toward landfall along the US Gulf coast. It should be noted that is considerable uncertainty with the intensity forecast.

Impacts:
For now will start increasing seas and tides on Sunday and bring squalls toward the coast and inland on Monday. Should the forecast track continue to in its current trajectory, tropical storm conditions will begin to spread across our coastal waters on Monday night and to the coast early Tuesday morning. Will leave it at that for now…given the uncertainty and potential for track and intensity changes.

Actions:
Review hurricane supply kits and plans and be ready to enact those plans this weekend.
Monitor forecasts from trusted sources at least twice per day