ATL: ISAAC - Post-Tropical - Discussion

[NDG]

[supercane4867]

Probably a hurricane already

[NDG]

Next 48 hrs SHIPS has windshear under 10 knots so no problem with the dry air to the west of it in the meantime. It looks like it is close to being a hurricane if not already.

[cycloneye]

BULLETIN
Tropical Storm Isaac Advisory Number 9
NWS National Hurricane Center Miami FL AL092018
500 PM AST Sun Sep 09 2018

...ISAAC ALMOST A HURRICANE...
...MOVING FASTER TOWARD THE WEST OVER THE TROPICAL ATLANTIC...


SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...14.5N 40.3W
ABOUT 1390 MI...2240 KM E OF THE WINDWARD ISLANDS
MAXIMUM SUSTAINED WINDS...70 MPH...110 KM/H
PRESENT MOVEMENT...W OR 275 DEGREES AT 12 MPH...19 KM/H
MINIMUM CENTRAL PRESSURE...997 MB...29.44 INCHES



Tropical Storm Isaac Discussion Number 9
NWS National Hurricane Center Miami FL AL092018
500 PM AST Sun Sep 09 2018

Isaac is a tiny tropical cyclone, but even still, recent SSMIS
data showed that it has developed a mid-level microwave eye
feature. At the time of the pass (1800 UTC), the convection was a
little thin on the southern side, but geostationary satellite images
suggest that it has filled in since that time. Dvorak intensity
estimates are T4.0 from TAFB and T3.5 from SAB, so the maximum
winds are estimated to be 60 kt.

The intensity forecast philosophy has not changed since this
morning. Isaac is strengthening in an environment of low shear and
over warm sea surface temperatures, and for the next 36-48 hours,
the NHC intensity forecast is above the bulk of the intensity
models. The main reason for this is that Isaac's tiny size could
allow the intensity to increase quickly within the favorable
environment. However, the cyclone's tiny size will likely also be
to its detriment after 48 hours when northwesterly vertical shear is
expected to develop and increase to 20-30 kt. The shear will
probably easily decouple the small system, causing the intensity to
decrease much faster than suggested by most of the intensity models.
For that reason, the official NHC intensity forecast is below the
intensity consensus on days 3 through 5. It should be noted that
both the GFS and ECMWF models show a weakening cyclone moving into
the eastern Caribbean Sea by days 4 and 5, with the GFS even making
the system an open wave by the end of the forecast period. These
global model solutions lend credence to the belief that it may be
difficult for Isaac to maintain hurricane status while it approaches
the Lesser Antilles.

Isaac is accelerating toward the west with an initial motion of
275/10 kt. Ridging to the north is expected to keep the cyclone on
a westward trajectory for the entire forecast period, with
acceleration continuing for the next 36 hours. The UKMET remains
the biggest outlier, showing Isaac turning northwestward and
northward into the central Atlantic after 48 hours. That still
appears to be unlikely at this time, and the NHC track forecast is
still close to the center of the guidance envelope. Only a slight
northward shift was made to the new forecast based on the latest
model solutions.


Key Messages:

1. Isaac is expected to become a hurricane tonight or on Monday
while it moves westward across the tropical Atlantic Ocean.

2. While Isaac is forecast to begin weakening by Tuesday while it
approaches the Lesser Antilles, it is still expected to be at or
near hurricane intensity when it reaches the islands, and the
uncertainty in the intensity forecast is higher than usual.
Interests in the Lesser Antilles should continue to monitor Isaac
during the next few days.


FORECAST POSITIONS AND MAX WINDS

INIT 09/2100Z 14.5N 40.3W 60 KT 70 MPH
12H 10/0600Z 14.6N 42.2W 70 KT 80 MPH
24H 10/1800Z 14.8N 45.0W 80 KT 90 MPH
36H 11/0600Z 14.9N 48.0W 85 KT 100 MPH
48H 11/1800Z 14.9N 50.9W 85 KT 100 MPH
72H 12/1800Z 15.0N 56.5W 70 KT 80 MPH
96H 13/1800Z 15.5N 63.0W 60 KT 70 MPH
120H 14/1800Z 15.5N 69.5W 50 KT 60 MPH

$$
Forecaster Berg

[SoupBone]

Next 48 hrs SHIPS has windshear under 10 knots so no problem with the dry air to the west of it in the meantime. It looks like it is close to being a hurricane if not already.

It's so damn tiny, like Beryl. Estimated 120 miles across, if that. If it does ramp up, it can just as easily lose strength quickly. It won't take much to disrupt it. Let's hope some dry air mixes in.

[cycloneye]

Key Messages:

1. Isaac is expected to become a hurricane tonight or on Monday
while it moves westward across the tropical Atlantic Ocean.

2. While Isaac is forecast to begin weakening by Tuesday while it
approaches the Lesser Antilles, it is still expected to be at or
near hurricane intensity when it reaches the islands, and the
uncertainty in the intensity forecast is higher than usual.
Interests in the Lesser Antilles should continue to monitor Isaac
during the next few days.

[cycloneye]

Key Messages:

1. Isaac is expected to become a hurricane tonight or on Monday
while it moves westward across the tropical Atlantic Ocean.

2. While Isaac is forecast to begin weakening by Tuesday while it
approaches the Lesser Antilles, it is still expected to be at or
near hurricane intensity when it reaches the islands, and the
uncertainty in the intensity forecast is higher than usual.
Interests in the Lesser Antilles should continue to monitor Isaac
during the next few days.

[CrazyC83]

Next 48 hrs SHIPS has windshear under 10 knots so no problem with the dry air to the west of it in the meantime. It looks like it is close to being a hurricane if not already.

It's so damn tiny, like Beryl. Estimated 120 miles across, if that. If it does ramp up, it can just as easily lose strength quickly. It won't take much to disrupt it. Let's hope some dry air mixes in.

Indeed, this could easily go up to a major tonight and then fall right back down. Or do just about anything. I would have added a point of rapid fluctuations in the key messages.

[Gustywind]

Next 48 hrs SHIPS has windshear under 10 knots so no problem with the dry air to the west of it in the meantime. It looks like it is close to being a hurricane if not already.

It's so damn tiny, like Beryl. Estimated 120 miles across, if that. If it does ramp up, it can just as easily lose strength quickly. It won't take much to disrupt it. Let's hope some dry air mixes in.

Indeed, this could easily go up to a major tonight and then fall right back down. Or do just about anything. I would have added a point of rapid fluctuations in the key messages.

That is why it's a vicious threat the way it continues to progresses westward towards the EC. We should monitor it carefully!

[cycloneye]

New microwave shows eye feature.

[CrazyC83]

New microwave shows eye feature.

Since Dvorak often underestimates midgets, I'd go with 75 kt right now personally. But if it clears out, we might need a special advisory.

[NDG]

Yeah, most likely a hurricane already.
Close up shots:

[Hammy]

Going to go out on a limb here and say Isaac was a hurricane earlier but didn't occur at the correct time to get upgraded--convection looks less organized on satellite now than earlier.

[SoupBone]

Going to go out on a limb here and say Isaac was a hurricane earlier but didn't occur at the correct time to get upgraded--convection looks less organized on satellite now than earlier.

It's such a tiny system that it's not hard to quickly lose and gain strength.

[AubreyStorm]

Hi folks!

Latest SSD on Isaac????

[Extratropical94]

TXNT24 KNES 100025
TCSNTL

A. 09L (ISAAC)

B. 09/2345Z

C. 14.6N

D. 41.1W

E. THREE/GOES-E

F. T4.0/4.0/D1.0/24HRS

G. IR/EIR/SWIR/SSMIS

H. REMARKS...CENTER IS EMBEDDED IN LG RESULTING IN A DT OF 4.5. MET AND
PT = 4.0. FT IS BASED ON MET.

I. ADDL POSITIONS

09/2101Z 14.6N 40.3W SSMIS


...KIBLER

[Nimbus]

Tiny eye draws much less inflow so it can easily provide its own moisture from the CDO rain canopy.
That is bad news, but NHC predicted cat 2 in the drier environment so..

[Blinhart]

TXNT24 KNES 100025
TCSNTL

A. 09L (ISAAC)
B. 09/2345Z
C. 14.6N
D. 41.1W
E. THREE/GOES-E
F. T4.0/4.0/D1.0/24HRS
G. IR/EIR/SWIR/SSMIS
H. REMARKS...CENTER IS EMBEDDED IN LG RESULTING IN A DT OF 4.5. MET AND PT = 4.0. FT IS BASED ON MET.
I. ADDL POSITIONS
09/2101Z 14.6N 40.3W SSMIS

...KIBLER

So wouldn't this suggest a Cat 1 hurricane??

[CrazyC83]

TXNT24 KNES 100025
TCSNTL

A. 09L (ISAAC)
B. 09/2345Z
C. 14.6N
D. 41.1W
E. THREE/GOES-E
F. T4.0/4.0/D1.0/24HRS
G. IR/EIR/SWIR/SSMIS
H. REMARKS...CENTER IS EMBEDDED IN LG RESULTING IN A DT OF 4.5. MET AND PT = 4.0. FT IS BASED ON MET.
I. ADDL POSITIONS
09/2101Z 14.6N 40.3W SSMIS

...KIBLER

So wouldn't this suggest a Cat 1 hurricane??

That is correct. In fact, I'd argue it is the strongest of the three storms out there now.

[Extratropical94]

According to 00Z Best Track we now have three simultaneous hurricanes in the Atlantic Ocean.

09L ISAAC 180910 0000 14.6N 41.0W ATL 65 993