update
Hurricane Frances Discussion Number 38
Statement as of 5:00 am EDT on September 03, 2004
Frances continues to slowly weaken. While it continues to generate
cold convective tops over the center...Air Force Reserve hurricane
hunter and Bahama radar data show that the tops are coming from
eyewall fragments in the northeastern quadrant. The minimum
central pressure has risen to 954 mb...and the maximum flight-level
winds on the last mission were 98 kt. The initial intensity is
reduced to 105 kt based primarily on the central pressure and
satellite intensity estimates...as the aircraft winds...including
dropsondes...do not currently support this intensity.
The initial motion is 300/8. Frances is on the southwest side of a
complex ridge that has one anticyclone center east of Frances and
another to the north. Large-scale models forecast heights to rise
north of Frances through 72 hr as a short wave ridge moves through
the eastern United States. After 72 hr...heights rise over the
western Atlantic as a trough develops over the central United
States. This pattern evolution should steer Frances west-
northwestward to northwestward for 24-36 hr...followed by some turn
toward the left and slower motion from 36-48 hr...then faster
motion toward the northwest and then north. NHC track guidance
generally agrees with this scenario...with a tight clustering of
guidance through the first 48 hr and and some spread between a
northwestward motion and a northward turn thereafter. The official
forecast is similar to...but slower than the previous package in
deference to the GFS and GFDL...which slow Frances to 4 kt just
prior to landfall on the Florida Peninsula. The forecast slow
forward speed will prolong the adverse and hazardous conditions
associated with Frances.
The intensity forecast is very problematic. On one side...the
hurricane wind field has become very spread out as the central core
weakens...and it is often difficult for this type of spread out
system to re-consolidate. Also...shear analyses from CIMSS at the
University of Wisconsin now show 15-20 kt of westerly shear across
Frances. The SHIPS model forecast this shear to persist until just
before landfall. On the other hand...the storm has a good cyclonic
envelope and is still generating strong convection. The intensity
forecast will go with the scenario that Frances will gradually
re-consolidate before landfall and re-gain some strength. An
alternative scenario is that Frances does not re-intensify or
perhaps weakens more as indicated by the SHIPS and GFDL models.
This part of the forecast is low confidence.
The 64 and 50 kt wind radii were modified in the NW quadrant based
on aircraft data...which reported a 95 kt flight-level wind 90 nm
northwest of the center.
At this time...changes in the warnings and watches are not
necessary.
Forecaster Beven
forecast positions and Max winds
initial 03/0900z 24.9n 76.0w 105 kt
12hr VT 03/1800z 25.7n 77.1w 110 kt
24hr VT 04/0600z 26.4n 78.3w 115 kt
36hr VT 04/1800z 27.1n 79.5w 120 kt
48hr VT 05/0600z 27.6n 80.7w 105 kt...inland
72hr VT 06/0600z 29.0n 83.0w 45 kt...over Gulf of Mexico
96hr VT 07/0600z 32.0n 86.0w 30 kt...inland
120hr VT 08/0600z 35.0n 86.5w 25 kt...inland
$$
Hurricane Frances Discussion Number 38
Statement as of 5:00 am EDT on September 03, 2004
Frances continues to slowly weaken. While it continues to generate
cold convective tops over the center...Air Force Reserve hurricane
hunter and Bahama radar data show that the tops are coming from
eyewall fragments in the northeastern quadrant. The minimum
central pressure has risen to 954 mb...and the maximum flight-level
winds on the last mission were 98 kt. The initial intensity is
reduced to 105 kt based primarily on the central pressure and
satellite intensity estimates...as the aircraft winds...including
dropsondes...do not currently support this intensity.
The initial motion is 300/8. Frances is on the southwest side of a
complex ridge that has one anticyclone center east of Frances and
another to the north. Large-scale models forecast heights to rise
north of Frances through 72 hr as a short wave ridge moves through
the eastern United States. After 72 hr...heights rise over the
western Atlantic as a trough develops over the central United
States. This pattern evolution should steer Frances west-
northwestward to northwestward for 24-36 hr...followed by some turn
toward the left and slower motion from 36-48 hr...then faster
motion toward the northwest and then north. NHC track guidance
generally agrees with this scenario...with a tight clustering of
guidance through the first 48 hr and and some spread between a
northwestward motion and a northward turn thereafter. The official
forecast is similar to...but slower than the previous package in
deference to the GFS and GFDL...which slow Frances to 4 kt just
prior to landfall on the Florida Peninsula. The forecast slow
forward speed will prolong the adverse and hazardous conditions
associated with Frances.
The intensity forecast is very problematic. On one side...the
hurricane wind field has become very spread out as the central core
weakens...and it is often difficult for this type of spread out
system to re-consolidate. Also...shear analyses from CIMSS at the
University of Wisconsin now show 15-20 kt of westerly shear across
Frances. The SHIPS model forecast this shear to persist until just
before landfall. On the other hand...the storm has a good cyclonic
envelope and is still generating strong convection. The intensity
forecast will go with the scenario that Frances will gradually
re-consolidate before landfall and re-gain some strength. An
alternative scenario is that Frances does not re-intensify or
perhaps weakens more as indicated by the SHIPS and GFDL models.
This part of the forecast is low confidence.
The 64 and 50 kt wind radii were modified in the NW quadrant based
on aircraft data...which reported a 95 kt flight-level wind 90 nm
northwest of the center.
At this time...changes in the warnings and watches are not
necessary.
Forecaster Beven
forecast positions and Max winds
initial 03/0900z 24.9n 76.0w 105 kt
12hr VT 03/1800z 25.7n 77.1w 110 kt
24hr VT 04/0600z 26.4n 78.3w 115 kt
36hr VT 04/1800z 27.1n 79.5w 120 kt
48hr VT 05/0600z 27.6n 80.7w 105 kt...inland
72hr VT 06/0600z 29.0n 83.0w 45 kt...over Gulf of Mexico
96hr VT 07/0600z 32.0n 86.0w 30 kt...inland
120hr VT 08/0600z 35.0n 86.5w 25 kt...inland
$$
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