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Hurricane GUILLERMO Forecast Discussion

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WTPZ44 KNHC 010833

200 AM PDT SAT AUG 01 2015

Guillermo's cloud pattern has changed little in organization over
the past several hours.  Convective banding features are not as
well defined as they were 24 hours ago, and the CDO lacks a circular
shape.  Dvorak T-numbers remain unchanged from the previous
advisory package, so the intensity estimate is held at 90 kt.
Upper-level outflow has become restricted to the northwest of the
cyclone.  The oceanic and atmospheric environment is not likely to
become more conducive for strengthening over the next couple of
days, and the numerical intensity guidance generally shows a
gradual weakening trend.  Near the end of the forecast period,
global models indicate a significant increase in vertical shear
associated with strong upper-tropospheric westerlies near the
Hawaiian Islands.  The official forecast is near or slightly above
the intensity model consensus and shows, as in the previous
advisory, weakening to tropical storm status in 96 hours.

Based on geostationary and microwave center fixes, in particular an
earlier SSMI/S pass from 0424Z, the motion has slowed somewhat and
is now estimated to be about 285/14 kt.  Guillermo is approaching a
weakness in the zonally-oriented mid-level ridge to its north, and
this should result in further deceleration over the next couple of
days.  In 3-5 days, the steering currents become less well defined
in the global models and there is a fair amount of spread in the
dynamical track predictions.  The ECMWF model has been doing a bit
of a flip-flop in its last few runs, and it has shifted back the
south after shifting northward in the previous run.  The official
forecast is held very close to the previous NHC track and is close
to the latest track model consensus, TVCN, which combines not only
the GFS and ECMWF solutions but also the HWRF, GFDL, and U.K. Met.
Office model forecasts.

Due to uncertainties in longer-range track predictions, it is
important for users not to focus on the exact track forecasts at 96
and 120 hours.


INIT  01/0900Z 13.4N 137.4W   90 KT 105 MPH
 12H  01/1800Z 13.9N 139.6W   90 KT 105 MPH
 24H  02/0600Z 14.5N 142.0W   90 KT 105 MPH
 36H  02/1800Z 15.1N 144.0W   85 KT 100 MPH
 48H  03/0600Z 15.8N 145.4W   75 KT  85 MPH
 72H  04/0600Z 17.3N 148.0W   65 KT  75 MPH
 96H  05/0600Z 19.0N 151.0W   60 KT  70 MPH
120H  06/0600Z 20.5N 154.0W   50 KT  60 MPH

Forecaster Pasch

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Page last modified: Saturday, 01-Aug-2015 08:33:57 UTC