ATL: ISAAC - Post-Tropical - Discussion

[HurricaneRyan]

Three hurricanes at once! This is low-key cool considering people thought this would be a dead season

[Yellow Evan]

I would not be surprised if Isaac and Helene become major hurricanes.

Current trends suggest that this is fairly likely even if it's a little tilted and sheared right now.

[MississippiWx]

Three hurricanes at once! This is low-key cool considering people thought this would be a dead season

I was one of those people talking about a dead season. It was extremely quiet until the last week. It's amazing what the MJO can do in the heart of the season to ignite even a slow year.

[cycloneye]

BULLETIN
Hurricane Isaac Advisory Number 11
NWS National Hurricane Center Miami FL AL092018
500 AM AST Mon Sep 10 2018

...ISAAC HOLDING STEADY IN STRENGTH OVER THE CENTRAL ATLANTIC...


SUMMARY OF 500 AM AST...0900 UTC...INFORMATION
----------------------------------------------
LOCATION...14.7N 42.7W
ABOUT 1230 MI...1985 KM E OF THE WINDWARD ISLANDS
MAXIMUM SUSTAINED WINDS...75 MPH...120 KM/H
PRESENT MOVEMENT...W OR 275 DEGREES AT 13 MPH...20 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 11...Corrected
NWS National Hurricane Center Miami FL AL092018
500 AM AST Mon Sep 10 2018

Corrected intensity forecast in table below.

Isaac has generally changed little during the past several hours.
The small hurricane continues to have a central dense overcast
feature with some fragmented bands to the south of the center. The
Dvorak classifications remain 4.0/65 kt from both TAFB and SAB, and
therefore, the initial intensity is held at 65 kt.

Isaac is moving westward at 11 kt. The models remain in poor
agreement this cycle as they are split into two camps. The UKMET,
HWRF, and a few other models show Isaac recurving near or to the
east of the Lesser Antilles toward a developing trough over the
central Atlantic. Conversely, the GFS and ECMWF have been very
consistent in showing a due westward motion across the Lesser
Antilles and into the Caribbean as the cyclone moves on the south
side of a strengthening mid-level ridge. The NHC track forecast
continues to favor the usually more reliable GFS and ECMWF models,
and this forecast is near a blend of those aids. It should be
noted, however, that confidence in this track forecast is low given
the model spread.

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. Given that the wind shear
is expected to remain less than 10 kt for another day or two,
strengthening is forecast during that time period. After that,
however, an increase in shear first from a trough over the central
Atlantic and later from the outflow from Florence should result in
weakening when the system moves across the Lesser Antilles and into
the Caribbean Sea. The NHC intensity forecast is not too different
from the previous one and lies above the model consensus in the
short term, but below it at the later forecast times. This
forecast is in best agreement with the latest LGEM guidance.

Key Messages:

1. Isaac is a small hurricane and uncertainty in the forecast is
higher 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 10/0900Z 14.7N 42.7W 65 KT 75 MPH
12H 10/1800Z 14.8N 44.6W 70 KT 80 MPH
24H 11/0600Z 15.0N 47.4W 75 KT 85 MPH
36H 11/1800Z 15.0N 50.3W 80 KT 90 MPH
48H 12/0600Z 15.0N 53.0W 80 KT 90 MPH
72H 13/0600Z 15.3N 58.0W 70 KT 80 MPH
96H 14/0600Z 15.5N 64.0W 60 KT 70 MPH
120H 15/0600Z 15.6N 69.2W 50 KT 60 MPH

$$
Forecaster Cangialosi

[Gustywind]

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

[Gustywind]

Latest SSD... stay at 4.0/4.0

10/0545 UTC 14.6N 42.1W T4.0/4.0 ISAAC

[NDG]

Glad to see that Isaac didn't strengthen overnight, still has another 36 hrs or so before shear starts affecting the hurricane.

[northjaxpro]

Three hurricanes at once! This is low-key cool considering people thought this would be a dead season

I was one of those people talking about a dead season. It was extremely quiet until the last week. It's amazing what the MJO can do in the heart of the season to ignite even a slow year.

This goes to show everyone just how quickly the dynamics can change in the tropics.

Never underestimate the volatility of the tropics, apparently Mother Nature decided to have these cyclones to truly occur exactly at the peak time of the season for 2018: September.

[abajan]

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.

[Gustywind]

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.

[TheStormExpert]

Isaac looks quite ragged this morning.

[1900hurricane]

Microwave presentation has degraded.

[SoupBone]

Isaac looks quite ragged this morning.

Yep, this is what we were talking about yesterday. These tiny little systems can ramp up quickly, but can also ramp right down quickly too. It still has some time before it reaches the islands to ramp back up, but let's hope it doesn't.

[Hypercane_Kyle]

Isaac looks more like a low-end TS than a hurricane this morning.

[cycloneye]

 https://twitter.com/TropicalTidbits/status/1039123022538571777

[cycloneye]

Hanging there as Hurricane.

AL, 09, 2018091012, , BEST, 0, 147N, 433W, 65, 993, HU

[Gustywind]

Maitaining T numbers at 4.0/4.0

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

[USVIKimmie]

Glad to see that Isaac didn't strengthen overnight, still has another 36 hrs or so before shear starts affecting the hurricane.

For some reason the link I have for this one isn't working any more (not your image, the site it came from). Any ideas or maybe I've got an old link?

Definitely glad to see it didn't gain strength over night.

[NDG]

Glad to see that Isaac didn't strengthen overnight, still has another 36 hrs or so before shear starts affecting the hurricane.

https://i.imgur.com/i8exbzT.jpg

For some reason the link I have for this one isn't working any more (not your image, the site it came from). Any ideas or maybe I've got an old link?

Definitely glad to see it didn't gain strength over night.

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

[drezee]

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.