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Tropical Storm VANCE Forecast Discussion

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WTPZ41 KNHC 312055

200 PM PDT FRI OCT 31 2014

Vance has a peculiar structure this afternoon.  The central
convection has become somewhat skeletal with the center exposed at
times, although there are still plenty of curved banding features in
the outer portion of the circulation. The culprit for this decrease
in convection appears to be an influx of dry air moving into the
central region of the tropical cyclone around the west and south
sides.  Dvorak estimates still support an intensity of about 40 kt.

Since the dry air is close to the center now, it will probably take
some time for this air to mix out.  Thus little change is shown in
the short term.  Afterward, models insist that the large-scale
environment will become favorable for strengthening over the next
three days or so.  Strong southwesterly shear is anticipated for the
beginning of next week, which will probably cause Vance to weaken
significantly at long range.  There has not been much change to the
guidance suite, with the majority of the guidance still showing
Vance as a hurricane in a few days.  The NHC forecast is therefore
very close to the previous one, and generally lies between the
intensity consensus and the SHIPS model.

It seems that finally the motion of Vance has become more clear, now
moving west-southwestward at about 6 kt.  This general motion is
expected through tonight due to a ridge over the eastern Pacific.
This ridge should move eastward over the next few days, steering the
cyclone more westward tomorrow, and to the northwest by late this
weekend. Vance is then forecast to turn northward and then north-
northeastward ahead of a trough moving over Baja California. Subtle
differences in the speed of the trough are leading to increased
model spread at long range, with the faster ECMWF preferring a more
north-northeast track, compared to the slower GFS solution of a
sharper northeastward turn.  The NHC forecast is adjusted westward
at day 3 and beyond, and is close to a dynamical model consensus
excluding the UKMET model, which has an improbable forecast due to a
seemingly spurious interaction with a weak ITCZ disturbance.


INIT  31/2100Z  9.5N 101.4W   40 KT  45 MPH
 12H  01/0600Z  9.3N 102.4W   40 KT  45 MPH
 24H  01/1800Z  9.6N 104.1W   45 KT  50 MPH
 36H  02/0600Z 10.5N 106.2W   55 KT  65 MPH
 48H  02/1800Z 11.7N 108.4W   65 KT  75 MPH
 72H  03/1800Z 16.0N 110.5W   70 KT  80 MPH
 96H  04/1800Z 19.8N 108.5W   50 KT  60 MPH
120H  05/1800Z 23.5N 106.0W   30 KT  35 MPH...INLAND

Forecaster Blake

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Page last modified: Friday, 31-Oct-2014 20:55:38 UTC