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Tropical Depression ELEVEN (Text)


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TROPICAL DEPRESSION ELEVEN DISCUSSION NUMBER   3
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL112015
1100 AM AST MON SEP 28 2015

Satellite imagery indicates that the depression's overall cloud
pattern has become better organized since yesterday despite
persistent north- northwesterly shear of about 20 kt.  The exposed
low-level center is located near the northwestern tip of a curved
band over the southeastern quadrant of the circulation. However,
satellite data indicate that the low- to mid-level centers have
recently become more separated.  Dvorak intensity estimates are a
consensus T2.0/30 kt from TAFB and SAB, so the initial intensity is
held at 30 kt.

Smoothing fixes over the last 12 hours yields an initial motion of
300/04, a little faster than before.  The depression is embedded in
low- to mid-level southeasterly flow around a ridge to its
northeast, with northwesterly flow aloft.  This synoptic pattern
should only favor a slow northwestward motion for the next couple of
days.  After 48 hours, the cyclone should reach the western end of
the low- to mid-level subtropical ridge and begin to respond to the
southerly and southwesterly flow ahead of a baroclinic trough
nearing the U.S. east coast.  This change to the steering should
result in a gradual northward turn with increasing forward speed.
The new track forecast is a little left of the previous one at 48
hours and a little faster, close to a blend of the GFS and ECWMF
model solutions.

GFS- and ECMWF-based SHIPS model output indicates a continuation of
moderately strong north-northwesterly shear over the cyclone for the
next day or so.  Even though other large-scale factors are generally
conducive for intensification during this time, shear of this
magnitude suggests that only slow intensification is possible. While
the shear should decrease some by 36 hours, other environmental
factors are not forecast to be as conducive and little further
strengthening is indicated.  Large-scale models depict the cyclone
merging with a frontal zone offshore of the Mid-Atlantic or New
England coasts by 96 hours, and the system is therefore shown to be
post-tropical at that time.  An alternate lower probability scenario
is that the cyclone could race ahead of the frontal boundary and
retain its tropical characteristics for a bit longer. The new
intensity forecast is above the previous one through 24 hours and
near the multi-model consensus but below the statistical-dynamical
guidance after that time due to more reliance on the global models
which show little further intensification.





FORECAST POSITIONS AND MAX WINDS

INIT  28/1500Z 27.8N  69.6W   30 KT  35 MPH
 12H  29/0000Z 28.1N  70.0W   40 KT  45 MPH
 24H  29/1200Z 28.5N  70.6W   40 KT  45 MPH
 36H  30/0000Z 29.1N  71.4W   40 KT  45 MPH
 48H  30/1200Z 29.6N  72.0W   40 KT  45 MPH
 72H  01/1200Z 32.0N  72.9W   35 KT  40 MPH
 96H  02/1200Z 37.7N  72.9W   35 KT  40 MPH...POST-TROPICAL
120H  03/1200Z...DISSIPATED

$$
Forecaster Kimberlain

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Page last modified: Thursday, 31-Dec-2015 12:09:22 UTC