Today's PREDICT Ensemble Discussion
Posted by JAC on 9/2/2010, 8:31 am
PREDICT Ensemble Discussion

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Date(UTC): 2010/09/02 11:46
Author: Ryan Torn
Submitted at(UTC): 2010/09/02 12:08
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Current Conditions/Review of Yesterday's Forecast:
Earl (PGI34L) continues to move up the east coast.  The ensemble
is doing well with the track of Earl; however, without proper
resolution, the intensity of the storm in the model is far less
than the actual storm. In contrast to Earl, the ensemble has
been having more difficulty with Fiona's (PGI36L) position over
the past two days.  In general, the ensemble appears to be
tending south of the actual storm, at least in the initial
positions.  The ensemble has been continuously bearish on this
system and may actually be trying to weaken it too soon.
Similar to Fiona, Gaston (PGI38L) has been another problematic
system for the ensemble.  Many ensemble members have been having
difficulty identifying a circulation maximum in the forecasts,
and the ensemble has been suggesting this system would not
develop for another couple of days.  Over the past day, the
initial positions of Gaston have been improving, which suggests
that observations are slowly, but surely correcting the initial
condition errors with this system.  PGI39L is just on the edge
of the domain, so I am hesitant to put too much stock in
forecasts of this system.  PGI40L is outside the domain at 0 h.

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DAY 1 (Next 24 hours) Outlook:
Earl moves up the east coast; the position variance is fairly
small and uniform in all horizontal directions.  Fiona moves to
the northwest away from the islands, unlike the other dynamical
models, which take it more northward.  While the MSLP increases
in all ensemble members, the circulation values remain roughly
the same.  Gaston barely moves over the first 24 h.  All of the
quantitative measures of Gaston's intensity also do not change
within the ensemble.  PGI39L also does not move much during this
period.  While the circulation values are near INVEST
designation, the thickness anomalies are quite small at this
point.

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DAY 2 (24 - 48 hours) Outlook:
Earl is accelerating up the East coast and has uniform position
variance in all directions.  The tracks of Fiona are starting to
bifurcate, with some members moving to the SW and others moving
to the NW.  The position variance is actually quite large for
such a short-term forecast.  Regardless, the circulation and
thickness values are decreasing in all of the ensemble members,
which suggest the system is dissipating.  Gaston also does not
move much during this 24 period, with the position variance
stretched in the E-W direction.  While most ensemble members
show Gaston gaining strength during this period, a few members
show the TS intensifying even quicker than the ensemble mean.
PGI39L shows little movement also; however, the circulation and
thickness anomaly values are still below genesis criteria for
all ensemble members.

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Extended Outlook:
Earl is now into the Canadian Maritimes and is still
characterized by uniform position variance.  Fiona continues to
show two sets of positions, one to the SW and one set to the NE.
The ensemble mean circulation is near zero by 72 h, which
suggests the system does not exist anymore.  Gaston is slowly
moving westward.  The ensemble-mean circulation values are now
at genesis criteria, though the thickness values are too small.
This uptick in intensity metrics suggests the ensemble thinks
this system is ready to develop into a full-fledged TC.  PGI39L
does not show much change from 48 h; however, the circulation
values are starting to creep up toward genesis criteria.  The
thickness values are less than criteria in all members.
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Latest Ensembles - JAC, 9/2/2010, 7:39 am
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