Hurricane GONZALO

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HURRICANE GONZALO DISCUSSION NUMBER  10
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL082014
500 PM AST TUE OCT 14 2014

Data from an Air Force Reserve Hurricane Hunter aircraft earlier
today indicated flight-level and SFMR wind data that were just below
the threshold of a major hurricane. On the last flight leg, the
aircraft measured a central pressure of 971 mb, which was down 2 mb
from what was measured at the start of the mission. The eye had also
contracted from a 20 nmi diameter down to about 16 nmi on the last
report. Recent data from the NOAA Doppler radar in San Juan indicate
that the eye has contracted to about 15 nmi at an altitude of about
36,000 ft since the aircraft departed a few hours ago, signifying
that the eye diameter is likely smaller at lower altitudes. In
addition, satellite imagery indicates that the eye has cleared out
and warmed while cloud tops have cooled significantly in the
surrounding eyewall. Based on the trends noted in the radar and
satellite data, the intensity has been increased to 100 kt, which is
supported by a UW-CIMSS ADT value of T5.4/100 kt.

Gonzalo continues to move steadily northwestward with a motion of
320/11 kt. The NHC model guidance is tightly packed and remains is
in excellent agreement on Gonzalo moving steadily northwestward
around the periphery of a deep-layer ridge located to its north
during the next 36 hours or so. By 48 hours, a deep mid-tropospheric
trough and cold front are expected to move eastward across the
Bahamas and weaken the western portion of the ridge. This should
allow the cyclone to turn slowly northward, and then accelerate
northeastward by 72 hours ahead of the aforementioned trough and
front, with the hurricane potentially threatening Bermuda on Day 3.
Gonzalo is expected to merge with the cold front or become
extratropical by 120 hours. The new track forecast is just an update
of the previous advisory track, and lies close to a blend of the
GFEX and TVCA consensus models.

With the eye of Gonzalo having contracted and become more distinct
in satellite, radar, and recon wind data, the system appears primed
for intensification into a category 4 hurricane later tonight or
on Wednesday. Sea-surface temperatures ahead of the cyclone are
sufficiently warm enough at 28C-28.5C to support a category 4
hurricane through at least the next 36 hours. The global models
continue to indicate that the best vertical shear conditions and 200
mb upper-level outflow pattern are expected to occur on Wednesday
and continue into Thursday morning. Afterwards, eyewall cycles and
possible cold upwelling beneath the hurricane are likely to cause
some fluctuations in the intensity. By 72 hours, increasing vertical
wind shear ahead of the aforementioned deep trough is expected to
induce weakening. By 120 hours, Gonzalo will be over sub-20C SSTs in
the North Atlantic and experiencing vertical shear of 50-60 kt,
which should result in the cyclone becoming an extratropical low.
The NHC intensity forecast is similar to the previous advisory and
remains above all of the available intensity guidance.

FORECAST POSITIONS AND MAX WINDS

INIT  14/2100Z 21.2N  66.0W  100 KT 115 MPH
 12H  15/0600Z 22.5N  67.1W  110 KT 125 MPH
 24H  15/1800Z 24.0N  68.2W  115 KT 130 MPH
 36H  16/0600Z 25.4N  68.7W  120 KT 140 MPH
 48H  16/1800Z 27.2N  68.3W  110 KT 125 MPH
 72H  17/1800Z 32.0N  65.6W  100 KT 115 MPH
 96H  18/1800Z 39.9N  60.4W   85 KT 100 MPH
120H  19/1800Z 49.0N  50.0W   65 KT  75 MPH...POST-TROP/EXTRATROP

$$
Forecaster Stewart

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