Tropical Storm Chantal

Chantal has changed little in organization on satellite imagery over
the past few hours.  Convective banding features are not yet well
defined...and the cloud pattern is currently a little
ragged-looking in appearance. 
 
 

 







 
 Dvorak T-numbers from TAFB and SAB
remain 2.5...so the intensity estimate is held at 35 kt for this
advisory.  The vertical shear over the area is not strong at this
time...but the SHIPS model indicates that westerly shear will
increase in 1-2 days.  Also...climatology suggests that tropical
cyclones that move rapidly westward or west-northwestward in the
deep tropics have difficulty strengthening.  The official intensity
forecast is the same as the previous one through the forecast
period...and close to the model consensus through 48 hours.  Beyond
2 days...it is expected that Chantal will have interacted with the
land masses of Hispaniola and eastern Cuba...which should cause
weakening in the 3-4 day time frame.  Near the end of the forecast
period...the global models show upper-tropospheric westerlies over
the forecast track and this should lead to further weakening. 
Confidence in the 3-5 day intensity forecast...however...is not
high.
 
 
 

 







 
 
Latest satellite fixes indicate that a rapid westward motion...
280/23...is continuing.  There are no big changes to the track
forecast reasoning from the previous advisory.  Chantal is expected
to move quickly toward the west-northwest to the south of a
pronounced mid-level ridge for the next day or so.  A strong high
pressure cell over the southwest North Atlantic should result in a
continued west-northwestward motion in 2-3 days.  Thereafter...a
weakness in the ridge over the eastern Gulf of Mexico and the
Florida Peninsula should lead to a turn toward the northwest and
north-northwest.  The official track forecast is very similar to
the previous one...and to the latest model consensus...through 48
hours.  At 3-5 days...the NHC track is shifted just slightly east
of the previous one.  The GFS...one of the few dynamical models to
maintain a coherent vortex through day 5...is farther to the east
of the official forecast.