5pm Discussion

[seahawkjd]

Hurricane Isabel Discussion Number 43


Statement as of 5:00 PM EDT on September 16, 2003



recent fixes from NOAA and Air Force reserve hurricane hunter
aircraft indicate that the weakening trend has ended...at least for
the time being. The most recent peak flight-level wind reported by
the Air Force aircraft was 111 kt over a very small area in the
northeast quadrant...and the crew indicated an improved radar
presentation. Before increasing the advisory intensity...we would
like to make sure these winds are representative. While the
outflow pattern has been improving today...the core convection is
still rather thin.
The initial motion remains 330/7. There continues to be no
significant change to the track forecast. Isabel is on the west
side of a deep-layer ridge extending from the Canadian Maritimes
south-southeastward to east of the hurricane. A broad area of
westerly flow is over the central and eastern United States...with
a shortwave trough lifting northeastward from the Great Lakes.
Large-scale models indicate that the ridge should build westward as
the shortwave lifts out. This could cause the track to Bend
slightly to the left of the current heading...and this is reflected
in the official forecast.

Most of the dynamical models continue to forecast the development of
a more favorable upper-level anticyclonic outflow pattern as Isabel
approaches the coast. Water-vapor imagery shows a short wave
trough extending into the Gulf of Mexico along 90w. The models dig
this short wave to the southwest of Isabel...creating an outflow
channel over the western periphery of the hurricane. The explicit
intensity guidance...the ships and GFDL models...now show some
reintensification.
Wind radii have been expanded based on data from the stepped
frequency microwave radiometer onboard the NOAA p-3 aircraft.

Note...the hurricane hunter aircraft recently reported a pressure of
958 mb.
Forecaster Franklin

forecast positions and Max winds

initial 16/2100z 27.8n 71.4w 90 kt
12hr VT 17/0600z 28.6n 71.9w 90 kt
24hr VT 17/1800z 30.5n 73.0w 90 kt
36hr VT 18/0600z 32.7n 74.6w 90 kt
48hr VT 18/1800z 35.0n 76.7w 95 kt...inland
72hr VT 19/1800z 41.5n 79.5w 30 kt...inland
96hr VT 20/1800z 50.0n 76.5w 30 kt...extratropical
120hr VT 21/1800z...absorbed by extratropical low