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HURRICANE JOAQUIN DISCUSSION NUMBER  38
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL112015
1100 PM AST TUE OCT 06 2015

Until just a couple of hours ago, Joaquin continued to display
a tight inner core, with deep convection surrounding a 20
n mi diameter eye.  The most recent geostationary infrared imagery
is finally showing that the convection is becoming asymmetric with
the 25 kt of tropospheric vertical shear adversely affecting the
cyclone.  The intensity remains 70 kt, since both the SAB and TAFB
Dvorak Current Intensity values are unchanged.

The hurricane is about to cross over the north wall of the Gulf
Stream and will be traversing very chilly 21-22C waters by tomorrow.
The combination of cold SSTs, dry air, and strong vertical shear
should cause the deep convection to either completely dislocate or
cease and the forecast calls for Joaquin to become a strong
post-tropical cyclone in about a day.  The FSU Cyclone Phase Space
diagrams, based upon the global and regional models, suggest that
Joaquin will gradually become more frontal and extratropical
transition is anticipated by Thursday.  Baroclinic forcing should
allow for only a gradual winding down as depicted by the models, and
dissipation is anticipated in about five days.

Joaquin is moving toward the east-northeast at a rather quick pace
of 25 kt, as it is being advected along by the mid-latitude
westerlies.  The system should accelerate east-northeastward for
about 36 hours, before slowing down in the eastern north Atlantic.
The track forecast is based upon the tightly clustered global and
regional models through 72 hours.  By day four, the guidance becomes
divergent with some solutions turning northeastward toward
Ireland and Great Britain, but most turning east-southeastward
toward Portugal and Spain.  This latter scenario is the basis for
the track forecast at day 4.

The track, intensity, and wind radii forecasts from 36 hours and
beyond are based upon guidance provided by the Ocean Prediction
Center.

A last-minute-arriving ASCAT scatterometer pass indicated that
Joaquin continues to expand in size.  The 34- and 50-kt wind radii
analyses and forecasts were adjusted accordingly.

FORECAST POSITIONS AND MAX WINDS

INIT  07/0300Z 40.0N  53.1W   70 KT  80 MPH
 12H  07/1200Z 41.0N  47.7W   65 KT  75 MPH
 24H  08/0000Z 42.1N  39.3W   60 KT  70 MPH...POST-TROPICAL
 36H  08/1200Z 43.4N  31.2W   60 KT  70 MPH...POST-TROP/EXTRATROP
 48H  09/0000Z 44.7N  25.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
 72H  10/0000Z 44.0N  17.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
 96H  11/0000Z 43.0N  13.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
120H  12/0000Z...POST-TROP/EXTRATROP

$$
Forecaster Landsea

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