ATL: ISAAC - Post-Tropical - Discussion

[USVIKimmie]

Try this link.
https://www.nrlmry.navy.mil/TC.html

That's the one I have, and it keeps timing out. I'm using Safari on iPhone 7, if that makes a difference...

[SoupBone]

Issac is falling apart. I expect the CoC to out run the MLC temporarily. There is mid level northerly shear and a low level surge at the same time. Not dead yet, but will need to reach at least 45 W to get rid of it. Likely only a TS for the islands.

That would be much better news for them, not great, but better. I wonder if this is what the GFS and Euro were taking into account.

[cycloneye]

BULLETIN
Hurricane Isaac Advisory Number 12
NWS National Hurricane Center Miami FL AL092018
1100 AM AST Mon Sep 10 2018

...ISAAC SHOWING LITTLE CHANGE IN STRENGTH AT THIS TIME...


SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...14.7N 43.9W
ABOUT 1150 MI...1855 KM E OF THE WINDWARD ISLANDS
MAXIMUM SUSTAINED WINDS...75 MPH...120 KM/H
PRESENT MOVEMENT...W OR 275 DEGREES AT 14 MPH...22 KM/H
MINIMUM CENTRAL PRESSURE...993 MB...29.33 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.

Interests in the Lesser Antilles should monitor the progress of
Isaac.


Hurricane Isaac Discussion Number 12
NWS National Hurricane Center Miami FL AL092018
1100 AM AST Mon Sep 10 2018

Isaac's cloud pattern is currently a bit ragged-looking, with an
irregular CDO and limited convective banding. Dvorak intensity
estimates from both TAFB and SAB are 65 kt, and that value will be
used for the advisory. There is significant uncertainty in the
intensity forecast for this system. Vertical wind shear over the
hurricane is forecast to be weak to moderate during the next day or
so, which should allow Isaac to strengthen somewhat. By 48 hours,
however, the global models depict significantly stronger
northwesterly shear, associated with an upper-level trough over the
central Atlantic, affecting the tropical cyclone. Most of the
guidance does not show Isaac strengthening over the Caribbean. The
HWRF model is an outlier, strengthening Isaac into a major hurricane
later in the period, and it is the main contributor to high
consensus forecasts at days 3-5. The NHC intensity forecast is
above the model consensus through 72 hours and below it by the end
of the period.

Isaac continues to move westward, or 275/12 kt. A subtropical
ridge should be maintained to the north of the tropical cyclone for
the next several days, so a continued westward track seems likely.
The U. K. Met. Office model is an outlier and shows Isaac turning
northwestward and northward to the northeast of the Leeward Islands.
The official track forecast, like the previous one, follows the
other reliable global models and is also close to the HFIP corrected
consensus guidance.

Key Messages:

1. Isaac is a small hurricane and uncertainty in the forecast is
greater than normal. Although Isaac is forecast to begin weakening
when it approaches the Lesser Antilles, it is still expected to be
at or near hurricane intensity when it reaches the islands.

2. Interests in the Lesser Antilles should continue to monitor Isaac
during the next few days.

FORECAST POSITIONS AND MAX WINDS

INIT 10/1500Z 14.7N 43.9W 65 KT 75 MPH
12H 11/0000Z 14.9N 45.9W 70 KT 80 MPH
24H 11/1200Z 15.0N 48.7W 75 KT 85 MPH
36H 12/0000Z 15.0N 51.4W 75 KT 85 MPH
48H 12/1200Z 15.1N 54.0W 75 KT 85 MPH
72H 13/1200Z 15.4N 59.4W 70 KT 80 MPH
96H 14/1200Z 15.5N 64.5W 60 KT 70 MPH
120H 15/1200Z 15.7N 70.0W 50 KT 60 MPH

$$
Forecaster Pasch

[MississippiWx]

Isaac looks more like a tropical depression than a hurricane. Models that showed no strengthening look to be on to something. Something isn’t right in the mid and upper levels. Shear seems to be a problem. I remember seeing a graphic posted by Michael Ventrice that showed how the upper levels have been very convergent in this portion of the basin all season. This acts to kill convection. Isaac is only able to generate a small area of thunderstorms thanks to a small vigorous vortex. This probably explains the constant pulsing of convection as well. While islanders should keep watching, I have my doubts that this stays a hurricane or anything more than a moderate TS for long.

[SoupBone]

Isaac looks more like a tropical depression than a hurricane. Models that showed no strengthening look to be on to something. Something isn’t right in the mid and upper levels. Shear seems to be a problem. I remember seeing a graphic posted by Michael Ventrice that showed how the upper levels have been very convergent in this portion of the basin all season. This acts to kill convection. Isaac is only able to generate a small area of thunderstorms thanks to a small vigorous vortex. This probably explains the constant pulsing of convection as well. While islanders should keep watching, I have my doubts that this stays a hurricane or anything more than a moderate TS for long.

It absolutely has. It's one of the things I've been actively paying attention to this season. And it shows no signs of relenting.

[AtlanticWind]

GFS Stronger on 12z run

[AtlanticWind]

GFS 12z shows more threat to PR unfortunately. Isaac just south of PR at about 987 mb strength

[msbee]

Hi everybody. Martinica, Guadeloupe and the Northern Leewards ( Sint Marteen Sint Barth) are Under a yellow vigilance cyclone. See chart below:
http://www.meteofrance.gp/vigilance-antilles-guyane

Looks like its center will pass over Guadeloupe, Gusty. Hopefully, it's below hurricane strength when it does so, but to quote from the 5 AM NHC Forecast Discussion,

The intensity forecast is also quite uncertain. One of the complex
factors is Isaac's compact size as small hurricanes like this one
are more prone to quick intensity changes, both up and down. In
addition, the intensity guidance is in poor agreement as solutions
range from steady weakening from this point onward to the HWRF that
shows Isaac becoming a major hurricane.

Hello Abajan. Yes, you're right. Looks like Guadeloupe is really exposed on this latest projection. Let's hope that it stays at a bordeline cat 1 or strong TS but no more. Should all these forecasts verifies too. We all know how versatile those little things are. Keeping our fingers crossed.

Gusty, my fingers are crossed for you too. Stay safe.

[MississippiWx]

GFS 12z shows more threat to PR unfortunately. Isaac just south of PR at about 987 mb strength

Interesting. That’s the first global model to show anything that strong in a while.

[chaser1]

Looks to me to be a crushing lower "Southeast to Northwest" oriented mid to upper-jet flow that is significantly hampering Isaac's inner core and overall envelope from expanding at the moment. From these aging eyes, I'd say strong unidirectional shear exists between the 250mb - 400mb levels (maybe extending up to 200mb as evident by the total lack of expanding outflow in it's northeast to east quadrants. It's actually impressive that any increase in intensity has occurred up to now given how the LLC is not exactly flying off to the WNW itself. All that said, I'm beginning to wonder if in fact anything greater then minimal T. S. strength winds are fully reaching the surface right now. This might have (temporarily) degenerated into a vigorous low to mid level (500mb-850mb?) cyclone for the moment. Anyway, that's all conjecture and more importantly is that it would seem that its present westward motion should move Issac toward an area where upper level conditions should become more relaxed. Thereafter, I think there's a big question mark whether upper level shear from Florence or dryer mid level air will or will not play a role as Isaac approaches the Leewards.

[chaser1]

GFS 12z shows more threat to PR unfortunately. Isaac just south of PR at about 987 mb strength

Interesting. That’s the first global model to show anything that strong in a while.

Something to watch out for is Isaac to continue to struggle as it approaches the Leewards, and then hit that "sweet spot" as the GFS (and other globals perhaps) are beginning to indicate. Luckily, those in P.R. and all the islands in the E. Caribbean are all too leary of any and all east approaching tropical systems.

[Gustywind]

GFS 12z shows more threat to PR unfortunately. Isaac just south of PR at about 987 mb strength

Latest 12z show a cat 1 show crossing the southern tip of Guadeloupe and send it just South of PR as you mentionned hope no!

[Gustywind]

Hurricane Isaac stays at 4.0/4.0 and moving westward...

10/1745 UTC 14.5N 44.1W T4.0/4.0 ISAAC
10/1145 UTC 14.6N 43.1W T4.0/4.0 ISAAC

[cycloneye]

No changes in the 18z Best Track:

AL, 09, 2018091018, , BEST, 0, 144N, 444W, 65, 993, HU

[Gustywind]

No changes in the 18z Best Track:

AL, 09, 2018091018, , BEST, 0, 144N, 444W, 65, 993, HU

Luis, this little boy does not want to give up. Waouw, he battles against dry air, shear, i'm so amazed Let's continue to monitor carefully as it trecks west.

[abajan]

No changes in the 18z Best Track:

AL, 09, 2018091018, , BEST, 0, 144N, 444W, 65, 993, HU

Nothing except that its estimated latitude has dropped 3/10th of a degree! May just be a wobble, but we definitely need to keep an eye on this.

[artist]

Please post any evacuation orders, closings and observations here.
Prepare early, leave if ordered, and in doubt of low lying areas, and know you all are in our thoughts and prayers.
Be sure to check in as soon as you can, once power and cell service is restored.

Mods, can you sticky, please?

[AubreyStorm]

No changes in the 18z Best Track:

AL, 09, 2018091018, , BEST, 0, 144N, 444W, 65, 993, HU

Nothing except that its estimated latitude has dropped 3/10th of a degree! May just be a wobble, but we definitely need to keep an eye on this.

Hi abajan!
Any link or floater?
Tropical Tidbits not working

[Ubuntwo]

Was this meant to be for Florence?

[Blinhart]

Was this meant to be for Florence?

No Isaac is headed for land also.