000
WTNT43 KNHC 151454
TCDAT3

HURRICANE GONZALO DISCUSSION NUMBER  13
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL082014
1100 AM AST WED OCT 15 2014

Data from an Air Force reconnaissance aircraft indicate that
Gonzalo has strengthened a little. The maximum 700 mb flight-level
wind reported was 123 kt and the highest SFMR wind observation was
116 kt.  Based on these data, the initial wind speed is increased to
115 kt, making Gonzalo a category 4 hurricane on the Saffir-Simpson
Hurricane Wind Scale.  This is the first category 4 hurricane in the
Atlantic basin since Ophelia in 2011.  The aircraft data and
microwave images clearly show concentric eyewalls, with the
inner radius of maximum wind now only about 4-5 n mi from the
center.

Smoothing through the trochoidal oscillation of the eye yields an
initial motion estimate of 320/10 kt.  A high amplitude trough over
the eastern United States is expected to slowly move eastward during
the next couple of days, and will erode the subtropical ridge that
is currently steering Gonzalo.  This change in the large-scale
pattern should cause the hurricane to turn northward by early
Thursday and north-northeastward Thursday night and Friday, likely
bringing Gonzalo near Bermuda in about 2 days.  Beyond 48 hours, the
hurricane is forecast to accelerate generally northeastward.  The
track model guidance remains tightly clustered, and the official
forecast is near the GFS and ECMWF solutions and only slightly to
the left of the previous one.

Given the evidence of concentric eyewalls, and with the inner
eyewall already about as small as it can get, the current period of
intensification could be about over.  The hurricane will likely
fluctuate in strength while the environmental conditions remain
favorable during the next day or two.  After that time, weakening
is forecast when the hurricane moves into an atmosphere of
increasing southwesterly shear and drier air, and over much colder
water.  Post-tropical transition will likely occur in 3 to 4 days
when the cyclone is forecast to cross the north wall of the Gulf
Stream current.  Little change was made to the previous intensity
forecast, and this one lies near the middle of the guidance
envelope.

FORECAST POSITIONS AND MAX WINDS

INIT  15/1500Z 23.5N  68.0W  115 KT 130 MPH
 12H  16/0000Z 24.6N  68.7W  115 KT 130 MPH
 24H  16/1200Z 26.3N  68.9W  115 KT 130 MPH
 36H  17/0000Z 28.6N  68.0W  110 KT 125 MPH
 48H  17/1200Z 31.6N  66.2W  105 KT 120 MPH
 72H  18/1200Z 40.6N  60.8W   90 KT 105 MPH
 96H  19/1200Z 50.5N  46.0W   65 KT  75 MPH...POST-TROP/EXTRATROP
120H  20/1200Z 54.0N  24.0W   50 KT  60 MPH...POST-TROP/EXTRATROP

$$
Forecaster Cangialosi