Hurricane JIMENA Forecast Discussion (Text)

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WTPZ43 KNHC 010245

800 PM PDT MON AUG 31 2015

Jimena is experiencing another eyewall replacement.  Satellite data
show a double eyewall structure within the hurricane's inner core,
with the eye having become cloud-filled and less defined throughout
the day. There has also been a dramatic warming of cloud top
temperatures during the past 12 hours or so.  Dvorak intensity
estimates have decreased substantially since the last advisory, and
a blend of latest Final T- and CI-numbers from TAFB and SAB is used
to lower the intensity to 115 kt.

Although the vertical wind shear should be extremely low and Jimena
should still be moving over SSTs greater than 28 deg C during the
next 48 hours, the intensity guidance shows slow weakening.  Neutral
thermodynamic conditions and a notable drop-off in oceanic heat
content along the cyclone's track likely contributes to a decrease
in intensity, at least in the statistical guidance.  Regardless,
internal dynamics in the hurricane's inner core are likely to
be key to the short-term intensity forecast, and given Jimena's
current structure of multiple wind maxima at large radii, it is
reasonable to expect a slow decay during the next few days. Only at
days 4 and 5 does westerly shear increase and the waters become
marginally warm.  That being said, the large-scale factors do not
support anything more than a slow filling.  The one caveat is that
the cyclone's slow movement could induce oceanic upwelling and
result in faster weakening.  The new intensity forecast is lowered
some from the previous one and is a bit lower than the multi-model
consensus after 24 hours, in best agreement with the FSU
Superensemble output.

The initial motion estimate is 285/14.  The tail of a mid-latitude
trough, extending south-southwestward from the Pacific Northwest, is
forecast to temporarily weaken the subtropical ridge between 140-
155W during the next day or two.  As a result, Jimena's forward
speed should decrease very soon, and the cyclone should continue to
gradually decelerate over the next couple of days. A northwestward
to north-northwestward drift in response to the weakness in the
ridge is shown by the global models from days 3 to 5.  The new track
forecast is close to the multi-model consensus, albeit not as far
east as the consensus in the latter part of the forecast period.


INIT  01/0300Z 16.3N 138.1W  115 KT 130 MPH
 12H  01/1200Z 16.6N 139.5W  105 KT 120 MPH
 24H  02/0000Z 17.2N 140.9W  100 KT 115 MPH
 36H  02/1200Z 17.8N 142.0W   90 KT 105 MPH
 48H  03/0000Z 18.3N 142.8W   85 KT 100 MPH
 72H  04/0000Z 19.2N 143.7W   75 KT  85 MPH
 96H  05/0000Z 20.5N 144.3W   65 KT  75 MPH
120H  06/0000Z 22.0N 144.9W   55 KT  65 MPH

Forecaster Kimberlain

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Page last modified: Tuesday, 01-Sep-2015 02:45:38 UTC