an Air Force hurricane hunter aircraft found that the minimum
pressure in Isidore has fallen to 984 mb...and the peak flight-level
winds were 76 kt. The crew also estimated surface winds of 70 kt.
On this basis...the advisory winds are increased to 65 kt...making
Isidore the second hurricane of the season.

Isidore has been basically on track today...and the initial motion
is 300/8. The short-term forecast is unchanged...taking Isidore
over western Cuba in 24 hours. In spite of copious quantities of
dropsondes having been released in the environment of Isidore from
the NOAA gulfstream-iv jet over the past two days...there remains
considerable divergence among the track guidance models beyond 48
hours. Much of this divergence appears to be related to the
forecast development of a cutoff mid- to upper-level low between
Bermuda and the Bahamas. The AVN has the strongest and most
westward version of this low...and the northeasterly flow around the
low may be why this model drives Isidore so strongly southwestward
near the end of the forecast period. For whatever reason...the AVN
ensemble mean does not take Isidore as far to the west as the AVN
control. The UKMET has flipped from its earlier northward
track...and is now in better agreement with the AVN. I remain
unconvinced that this low will be as strong or as west as the AVN is
forecasting. However...given the overall tendency for the guidance
to shift westward...I have nudged the official forecast westward
near 72 hours. The bottom line is that when Isidore gets into the
Gulf...steering currents will become very weak...and it will likely
meander and cause much anxiety for several days.

Now that Isidore has a well-formed core...the pace of
intensification should increase. The outflow pattern is well
established and the size of the cyclone is growing. Four out of
five of the ships rapid intensification predictors are positive.
The only slight negative factor over the next 36 hours will be
interaction with the cuban landmass. It is likely that Isidore will
be a major hurricane in the southeastern Gulf of Mexico.

Forecaster Franklin

forecast positions and Max winds

initial 19/2100z 20.6n 82.0w 65 kts
12hr VT 20/0600z 21.3n 83.1w 80 kts
24hr VT 20/1800z 22.4n 84.2w 85 kts
36hr VT 21/0600z 23.2n 85.0w 90 kts
48hr VT 21/1800z 23.5n 85.5w 100 kts
72hr VT 22/1800z 24.0n 86.5w 105 kts