Hurricane JIMENA Forecast Discussion (Text)

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WTPZ43 KNHC 300251

800 PM PDT SAT AUG 29 2015

Jimena continues to undergo an eyewall replacement, with significant
inner-core structural changes seen in satellite data throughout
the day.  Microwave images show a small inner eyewall rotating
around an irregularly-shaped outer eyewall at about 60 n mi radius,
the latter which could be slowly contracting.  Although Jimena's
cloud pattern has fluctuated some during this period of inner-core
change, its overall organization has remained about the same
since the last advisory.  Satellite classifications seem to bear
this out, with intensity estimates of T6.0/115 kt and T6.5/127 kt
from SAB and TAFB, respectively, at 0000 UTC.  These are blended
with the latest UW-CIMSS ADT value of 6.1/117 kt to keep the initial
intensity estimate at 120 kt.

The intensity forecast is challenging.  The large-scale environment
is forecast to remain relatively favorable during the next day or
two, apart from some north-northwesterly shear associated with a
cold low to the northeast of Jimena.  This could allow an
opportunity for reintensification if the current eyewall
replacement fully plays out, but predicting intensity fluctuations
due to inner-core dynamics is nearly impossible and beyond the
scope of this forecast. Thus, a slow decrease in intensity is
indicated in the new forecast as large-scale conditions only
gradually become less conducive.  This is a blend of the
statistical-dynamical guidance. As Jimena gradually gains latitude
later in the forecast period, global models show a minor increase in
westerly shear while other thermodynamic factor remain generally
neutral, except for slowly decreasing SSTs.  These factors suggests
a slow decay of the cyclone, and the new intensity forecast is in
agreement with the latest multi-model consensus that shows a
monotonic decrease in intensity from days 3 to 5.

The eye of Jimena has been wobbling quite a bit, but smoothing
through these yields a faster initial motion estimate of 295/11.
Jimena should continue moving west-northwestward during the next few
days as it approaches the western end of a subtropical ridge around
140W.  A weakness in the ridge around this longitude should induce a
significant deceleration by days 4 and 5.  The track guidance is in
excellent agreement through the first 2 days, with less-than-typical
spread beyond that time.  The new track forecast is faster and
adjusted slightly southward and then westward after day 3, but not
as far south or west as the multi-model consensus.


INIT  30/0300Z 13.3N 127.5W  120 KT 140 MPH
 12H  30/1200Z 13.9N 129.3W  115 KT 130 MPH
 24H  31/0000Z 14.7N 131.8W  110 KT 125 MPH
 36H  31/1200Z 15.4N 134.4W  110 KT 125 MPH
 48H  01/0000Z 16.0N 136.7W  105 KT 120 MPH
 72H  02/0000Z 16.9N 139.9W   95 KT 110 MPH
 96H  03/0000Z 17.6N 141.9W   85 KT 100 MPH
120H  04/0000Z 18.1N 143.4W   75 KT  85 MPH

Forecaster Kimberlain

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Page last modified: Sunday, 30-Aug-2015 02:51:33 UTC