HURRICANE ISAAC

[dafif]

No fishing in the gulf next week !!

[ROLLTIDE]

ZCZC MIATCDAT4 ALL
TTAA00 KNHC DDHHMM

Tropical Storm Isaac Discussion Number 25
NWS National Hurricane Center Miami FL AL092018
500 PM AST Thu Sep 13 2018

The center of Isaac has been mostly exposed during the past several
hours as temporary bursts of convection fire just east of the
center. Assuming some spin down of the circulation after the plane
left, the initial wind speed is set to 35 kt. Since there haven't
been any reports of sustained tropical-storm-force winds in the
Lesser Antilles and the center is moving away, all watches and
warning have been lowered. However, there remains a threat of flash
flooding due to a large area of rain that has yet to move through
the Lesser Antilles.

Strong shear and mid-level dry air is forecast to persist for the
next day or so, which should cause Isaac to drop back to tropical
depression status on Friday. However, the shear is forecast to
weaken by the weekend, and moisture values are expected to rise as
the system gets deeper into the Caribbean Sea. These conditions
would normally allow for some restregthening, but the initial
character of the system is pretty weak, and it is uncertain whether
there will be much left of Isaac to take advantage of the more
conducive conditions. Model guidance has been inconsistent on the
future of Isaac, which speaks to the lack of predictability of this
situation. The bulk of the guidance show Isaac staying weak or
degenerating into a tropical wave over the next few days, so the
official forecast follows that consensus. At this point it is
just best to keep an eye on the long-range forecast on each
advisory to see if there are any changes.

Isaac is moving westward at about 15 kt. A mid-level ridge is
forecast to persist over the southwestern Atlantic, steering Isaac
westward for the next few days, with a turn to the west-northwest
possible at long range. The future track is very uncertain at long
range because it is dependent on the intensity. If Isaac
degenerates into a wave, the remnants will likely move south and
west of the guidance mean, and if the cyclone is stronger, it will
probably move slower and more to the right. The new NHC forecast
assumes that Isaac will stay weak, and therefore is on the left and
faster side of the guidance.


FORECAST POSITIONS AND MAX WINDS

INIT 13/2100Z 14.9N 63.2W 35 KT 40 MPH
12H 14/0600Z 14.9N 65.4W 35 KT 40 MPH
24H 14/1800Z 14.9N 68.2W 30 KT 35 MPH
36H 15/0600Z 14.9N 70.8W 30 KT 35 MPH
48H 15/1800Z 15.0N 73.0W 30 KT 35 MPH
72H 16/1800Z 16.2N 77.4W 30 KT 35 MPH
96H 17/1800Z 17.5N 81.5W 30 KT 35 MPH
120H 18/1800Z...DISSIPATED

$$
Forecaster Blake

[ROLLTIDE]

207
WTNT44 KNHC 140832
TCDAT4

Tropical Depression Isaac Discussion Number 27
NWS National Hurricane Center Miami FL AL092018
500 AM AST Fri Sep 14 2018

Northwesterly shear continues to take a toll on Isaac. Although the
system is still producing areas of deep convection, an ASCAT
overpass that arrived shortly after the release of the previous
advisory, indicated that the circulation had become even less
defined. The ASCAT data also showed that the winds are below
tropical storm strength, therefore the initial intensity has been
reduced to 30 kt.

Moderate to strong northwesterly shear and dry mid-level air are
likely to cause additional weakening, and Isaac is forecast to
degenerate into an open wave within the next several days, but this
could occur much sooner if the current trends continue.
When the system reaches the western Caribbean Sea the shear may
relax somewhat and moisture levels are expected to be higher. These
conditions could allow for regeneration of the system, but the ECMWF
and GFS both show Issac weakening and moving over the western
Caribbean as an open wave, and the NHC forecast follows this
scenario.

A low- to mid-level ridge over the southwestern Atlantic continues
to steer Isaac westward, and this general motion should continue
until dissipation occur. The new track forecast is once again
essentially an update of the previous advisory.

FORECAST POSITIONS AND MAX WINDS

INIT 14/0900Z 15.0N 65.5W 30 KT 35 MPH
12H 14/1800Z 15.1N 67.3W 30 KT 35 MPH
24H 15/0600Z 15.2N 69.7W 30 KT 35 MPH
36H 15/1800Z 15.2N 72.0W 25 KT 30 MPH
48H 16/0600Z 15.4N 73.8W 25 KT 30 MPH
72H 17/0600Z 16.4N 77.7W 25 KT 30 MPH
96H 18/0600Z...DISSIPATED

$$
Forecaster Brown

[ROLLTIDE]

559
WTNT44 KNHC 150841
TCDAT4

Remnants Of Isaac Discussion Number 31
NWS National Hurricane Center Miami FL AL092018
500 AM EDT Sat Sep 15 2018

A NOAA Hurricane Hunter aircraft investigated Isaac over the past
few hours and was unable to identify a well-defined center. The
plane found multiple small and poorly-defined circulations embedded
within a larger area of weak and variable winds, well to the south
of the previous estimated center location. The plane also found that
the minimum pressure has risen to around 1006 mb. All of this data
confirmed what two late-arriving ASCAT overpasses from earlier this
evening indicated, that Isaac has opened up into a southwest to
northeast oriented trough. Since Isaac does not have a well-defined
center, it no longer meets the NHC definition of a tropical cyclone
and this is the last advisory.

The strongest SFMR winds found by the plane were around 30 kt,
mainly to the north of the deep convection, so the intensity has
been set at that value. Although some of the regional hurricane
models suggest that small short-lived circulations like the ones
found by the plane could temporarily spin up within the larger
envelope of the tropical wave over the next several days, none of
the dynamical models currently show any significant redevelopment of
Isaac. The wave will likely continue westward across the Caribbean
Sea over the next few days, producing gusty winds and occasional
heavy rains over portions of Hispaniola and Jamaica.

This is the last public advisory issued by the National Hurricane
Center on Isaac. Additional information can be found in High Seas
Forecasts issued by the National Weather Service, under AWIPS header
NFDHSFAT1, WMO header FZNT01 KWBC, and available online at
https://ocean.weather.gov/shtml/NFDHSFAT1.shtml.


FORECAST POSITIONS AND MAX WINDS

INIT 15/0900Z 14.8N 70.8W 30 KT 35 MPH
12H 15/1800Z...DISSIPATED

$$
Forecaster Zelinsky