Hurricane Frances Discussion Number 33
Statement as of 11:00 PM EDT on September 01, 2004
recon this afternoon and evening indciated the central pressure had
decreased to 939 mb. A dropsonde at 01/1904z indicated winds of 154
kt...or 177 mph...at the 850 mb level. The highest 700 mb recon
flight-level wind at 2210z was 134 kt...equal to about a 121-kt
surface wind. Based on this information...Frances is being held at
120 kt...which may be a little conservative.
The initial motion is 295/12. However...there has been considerbale
wobble in the track the past 12 hours due to the eyewall replacement
cycles that have been occurring. Frances has been moving
west-northwestward for the past 24 hours under the influence of the
subtropical ridge to the north...which is expected to remain intact
through at least 48 hours. The Gulfstream-IV jet and an afres c-130
have been releasing dropsondes around the periphery of Frances. The
sonde data has produced some interesting and disturbing results.
The height data for the various pressure levels...compared to 18z
surrounding upper-air data...appear to be at least 20 meters too
low. However...the wind data clearly indicate a mid-tropospheric
high pressure center near 30n 75w...or about 500 nmi northwest of
Frances with a ridge axis extending west-southwestward across North
Florida and into the northeast Gulf of Mexico. In the short term...
this would suggest that Frances should continue moving at 295 or
even 290 degrees motion for the next 24 hours or so. Also...00z
upper-air data indicate that the 18z NOGAPS and 12z UKMET models
have verified the 00z 500 mb ridge and heights the best...while the
18z GFS and GFDL models were much too weak...at least 20 meters too
low...with the strength of the ridge. Since the 00z model runs will
have the new GPS dropsonde data included in those runs for the 06z
advisory...no significant change is being made to the previous
forecast track. However...with high pressure located to the
northwest of Frances...I would not be surprised to the 00z model
tracks shift a little more westward.
Frances is expected to move over warmer water near and within the
Bahama Islands chain in 24-48 hours. Given the already impressive
outflow pattern...some additional strengthening seems plausible.
Also...the very dry mid-level air...30-40 percent humidity...that
Frances has been traversing through and ingesting over the past 5
days is forecast to increase to more than 60 percent in 36-60hr...
which may also help with the intensification process.
Forecaster Stewart
forecast positions and Max winds
initial 02/0300z 22.6n 72.0w 120 kt
12hr VT 02/1200z 23.5n 73.7w 120 kt
24hr VT 03/0000z 24.7n 75.6w 125 kt
36hr VT 03/1200z 25.8n 77.3w 125 kt
48hr VT 04/0000z 26.6n 78.5w 125 kt
72hr VT 05/0000z 28.0n 81.0w 105 kt...inland
96hr VT 06/0000z 30.0n 83.0w 35 kt...inland
120hr VT 07/0000z 33.5n 85.0w 25 kt...inland