ATL: LEE - Post-Tropical Low - Discussion

[HurricaneRyan]

Wow. This came out of nowhere

[WeatherGuesser]

Tropical Storm Lee Discussion Number 20
NWS National Hurricane Center Miami FL AL142017
500 AM AST Sat Sep 23 2017

Not much has changed with Lee over the past six hours. The
convection previously observed in the SE quadrant appears to have
rotated around the tropical storm and faded, but a 0609 UTC SSMI
overpass indicates that a new burst has since taken its place.
Dvorak intensity estimates range from 30 to 35 kt, so the intensity
has been held at 35 kt for this advisory.

Every aspect of the forecast is highly uncertain. With regards to
intensity, the model forecasts range from dissipation (GFS) to
a category 2 or 3 hurricane (HWRF, HMON). Since the environment
still appears to be generally favorable for intensification, my
forecast remains close to the HWRF, and a little above the intensity
consensus through 72 h. The forecast shows gradual weakening after
that time as the shear increases. Because Lee is so small, it is
very possible that the tropical storm could strengthen far more
quickly than indicated here, at just about any time during the
forecast period. Likewise, rapid weakening could occur later in the
period if the shear increases like the SHIPS diagnostics indicate it
will.

As uncertain as the intensity forecast is, the track forecast may be
even more so. The ECMWF now shows a relatively deep Lee drifting
south for the next 72 hours, followed by a gradual turn toward the
northwest. On the other hand, the GFS continues to depict a shallow
Lee (or its remnants) moving steadily eastward through the forecast
period. As a result, these two typically reliable models differ by
more than 900 miles at day 5. The new official track forecast is
generally close to the corrected consensus models, FSSE and HCCA,
but hedges somewhat toward the ECMWF since it's version of Lee is
more in line with the NHC intensity forecast. As a result, the NHC
track forecast has been shifted significantly to the west,
especially at 72 h and beyond, but still lies nearly 400 miles to
the east of the ECMWF.

Needless to say, confidence in the forecast is low, and significant
changes to the track or intensity forecast may be required during
the next day or two.


FORECAST POSITIONS AND MAX WINDS

INIT 23/0900Z 31.9N 49.2W 35 KT 40 MPH
12H 23/1800Z 32.3N 49.1W 40 KT 45 MPH
24H 24/0600Z 32.5N 48.4W 45 KT 50 MPH
36H 24/1800Z 32.2N 47.4W 50 KT 60 MPH
48H 25/0600Z 31.7N 46.2W 60 KT 70 MPH
72H 26/0600Z 30.5N 44.5W 75 KT 85 MPH
96H 27/0600Z 29.8N 45.0W 70 KT 80 MPH
120H 28/0600Z 30.5N 46.5W 60 KT 70 MPH

$$
Forecaster Zelinsky

[NotSparta]

If it manages to stay together and circle south, then back west .... who knows what might happen?

Let's not go there. Okay?

It got 2017'd?

[Vince_and_Grace_fan]

It's bad that Lee hasn't got Recon, because he is possibly smaller than Marco (2008).

[AutoPenalti]

If this isn’t a micro-cane, this has to be close to a nano-cane.

[Hurricaneman]

It's bad that Lee hasn't got Recon, because he is possibly smaller than Marco (2008).

We can add this to the possible micro hurricane list with such systems as Charley 2004, Marco 2008, Iris 2001 and Tracy 1974

[supercane4867]

Lee is becoming much better organized this evening with spiral bands and an eyewall feature showing up on microwave imagery.
HWRF has Lee reach hurricane strength as early as tomorrow morning which I won't be surprised if it verifies.

[1900hurricane]

Lee might be close to hurricane intensity already honestly.

[Buck]

With Lee 2.0 forecast to become a hurricane, that would mean 8 hurricanes in a row (just counting Lee in general, not counting Lee 1.0 or Harvey 1.0)... I was looking at some obvious maybes (1950, 1995, 1969) and couldn't find a season with that many consecutive hurricanes. Anyone know?

[CrazyC83]

I would probably estimate the intensity at 60 kt. Dvorak can underestimate these nano-storms by one full T number or more.

[CyclonicFury]

I would probably estimate the intensity at 60 kt. Dvorak can underestimate these nano-storms by one full T number or more.

Agreed, 40 kt seems way too conservative for a storm like this.

[Sciencerocks]

I would probably estimate the intensity at 60 kt. Dvorak can underestimate these nano-storms by one full T number or more.

Agreed. That partly closed eyewall is a good sign of this based on microwave.

[Hammy]

Hurricane anyone?

[AutoPenalti]

I swear I feel like if it develops even a pin-hole eye it will just shred itself inside out.

[EquusStorm]

Kinda wish we had recon because this thing is definitely going to be underestimated. Definite proto-eye feature to go with eyewall developments earlier.

NHC has been unusually bold with this one, now forecasting a cat 1 to the end of 120h and suggesting RI (from a low end TS to maybe a high cat 1, I'd assume) is possible due to the tiny size. Doesn't seem to be bothering anyone at all so I say go for it! Let's break us some September ACE records

[supercane4867]

Here comes the warm spot. We should see an eye on visible imagery by sunrise.

[Sciencerocks]

I'd estimate it is now probably a hurricane.

[Sciencerocks]

000
WTNT44 KNHC 240625
TCDAT4

Hurricane Lee Special Discussion Number 24
NWS National Hurricane Center Miami FL AL142017
200 AM AST Sun Sep 24 2017

Infrared satellite imagery indicates that an eye is developing in
Lee's central dense overcast. This special advisory is thus being
issued to make Lee a hurricane with 65 kt winds. The intensity
forecast has been significantly increased based on the current
intensity and trends, and the initial wind radii have been somewhat
modified. However, the track forecast is unchanged from the
previous advisory.


FORECAST POSITIONS AND MAX WINDS

INIT 24/0630Z 31.9N 50.1W 65 KT 75 MPH
12H 24/1200Z 31.8N 50.0W 75 KT 85 MPH
24H 25/0000Z 31.5N 49.4W 85 KT 100 MPH
36H 25/1200Z 30.9N 48.9W 90 KT 105 MPH
48H 26/0000Z 30.2N 48.9W 90 KT 105 MPH
72H 27/0000Z 30.0N 50.5W 90 KT 105 MPH
96H 28/0000Z 31.5N 52.0W 85 KT 100 MPH
120H 29/0000Z 34.5N 52.5W 80 KT 90 MPH

$$
Forecaster Beven

[EquusStorm]

If Lee hits or exceeds its forecast peak, not only will every storm since Franklin have been a hurricane (as has happened) but every storm since Gert will have been at least a medium end category two. We are also probably going to break the one month ACE record, with Maria still active as well.

[EquusStorm]

Hurricane Lee Discussion Number 25
NWS National Hurricane Center Miami FL AL142017
500 AM AST Sun Sep 24 2017

Since the earlier special advisory issued to make Lee a hurricane,
the eye has become much better defined in IR imagery, indicating
that the hurricane has continued to rapidly intensify. The initial
intensity has therefore been increased to 75 kt, based on an
application of the Dvorak technique to the latest IR imagery. It
should be noted that in this case, the intensity is fairly uncertain
given the lack of ground truth and the small size of the cyclone.

At this point, it is hard to judge how long this period of rapid
intensification will continue. On one hand, Lee is expected to
remain in a relatively unstable and low-shear environment for the
next several days. On the other, despite the clearing of the eye,
cloud tops have not cooled significantly overnight, and the slow
motion of Lee allows the possibility that the storm could begin to
interact with its own cold wake. The NHC forecast brings Lee to
near major hurricane strength in 24 h, and then keeps Lee around
that intensity through day 4, similar to the FSSE model. By the end
of the forecast, higher shear, due in part to the outflow of
Hurricane Maria, could cause Lee to weaken, so the NHC forecast is a
little lower at that point.

Lee is drifting southward for now, but a southeastward motion is
still forecast to begin later today. Very little change has been
made to the NHC forecast, which is mainly just an update of the
previous one. The models have come into better agreement that Lee
will be primarily steered for the next several days by a mid-level
ridge building to the northwest. By day 5, a trough associated
with Maria and the subtropical ridge should cause Lee to begin
recurving. Since the model spread has decreased, confidence in
that aspect of the forecast has increased this morning.


FORECAST POSITIONS AND MAX WINDS

INIT 24/0900Z 31.8N 50.1W 75 KT 85 MPH
12H 24/1800Z 31.6N 49.6W 85 KT 100 MPH
24H 25/0600Z 31.1N 48.9W 95 KT 110 MPH
36H 25/1800Z 30.6N 48.8W 95 KT 110 MPH
48H 26/0600Z 30.2N 49.4W 95 KT 110 MPH
72H 27/0600Z 30.5N 51.3W 90 KT 105 MPH
96H 28/0600Z 32.0N 52.5W 90 KT 105 MPH
120H 29/0600Z 34.5N 51.4W 80 KT 90 MPH