#4 Postby srainhoutx » Thu Sep 30, 2010 7:54 am
From PREDICT...
PREDICT Ensemble Discussion
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Date(UTC): 2010/09/30 11:32
Author: Ryan Torn
Submitted at(UTC): 2010/09/30 12:00
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Current Conditions/Review of Yesterday's Forecast:
NHC upgraded TD16 to TS Nicole at 1500 UTC yesterday; however,
by 2100 UTC this system was downgraded to a non-tropical system
and will not be discussed here. PGI48L and PGI51L appear to
have merged together and are now designated PGI51L. The
ensemble has been predicting for this system to get close to
genesis criteria for the past three forecast cycles, though to
date, there does not appear to be any increase in the
circulation of this system during the past couple of days,
though there is plenty of convection. The initial position of
this system within the ensemble is just to the north of the
consensus. PGI49L has not shown much sign of getting better
organized since moving off the African coast. The ensemble has
been more bearish about the development of this system relative
to PGI51L because it encounters more shear as it moves to the
NW. The ensemble has the pouch fairly close to the consensus at
the initial time, but there is a lot of spread.
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DAY 1 (Next 24 hours) Outlook:
PGI49L continues to move to the northwest during the first
period of the forecast, with position variance stretched in the
E-W direction. There is a slow increase in the midtropospheric
circulation in all ensemble members; however, the OW values
remain nearly constant and near 1. PGI51L is predicted to be
over the windward islands by 24 h, with larger position variance
stretched in the NE-SW direction. The circulation values
associated with this system are predicted to nearly double
during this 24 h period, with the OW values becoming much
greater than zero.
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DAY 2 (24 - 48 hours) Outlook:
PGI49L continues to drift to the NW during this period, with the
ensemble-mean position near 17N 51W at 48 h, with large variance
stretched in the E-W direction. The circulation values continue
to increase during this period, with a few of the extreme
members reaching circulation and thickness genesis criteria by
the end of the period. PGI51L is forecast to be in the
Caribbean sea just to the south of the Virgin Islands by 48 h.
The position variance is stretched in the NW-SE direction during
this period. All of the members show continued strengthening of
this system during the period, though some members start to
level off the circulation values well below genesis criteria.
The minimum pressures associated with this system continue to
fall in all members.
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Extended Outlook:
PGI49L continues along the same NW trajectory, with a large
amount of position variance in the along-track direction. The
circulation values continue to increase in the ensemble mean,
nearly reaching genesis criteria by 72 h, though there is a
large amount of spread with some members decaying by 72 h and
others showing a robust TS. This is an excellent case for
initial condition sensitivity calculations given the large
uncertainty. PGI51L is nearly stationary during this period,
with some slow drift to the NW toward Hispaniola and Puerto
Rico. The position variance is stretched in the E-W direction
within the ensemble. The ensemble-mean circulation and
thickness anomaly values continue to increase during this period
and both exceed genesis criteria by 72 h. There are also a
number of members that predict these two metrics will remain
below genesis criteria, so this is also an uncertain forecast,
though it should be noted that the ensemble has been aggressive
with trying to develop this into a TD for the past three days,
thus I am not sure how much I trust this forecast.
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