PREDICT Synopsis: All ensembles show Gaston re-genesis in 48 hrs
Posted by
JAC on 9/8/2010, 8:49 am
PREDICT Ensemble Discussion
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Date(UTC): 2010/09/08 12:01
Author: Ryan Torn
Submitted at(UTC): 2010/09/08 12:23
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Current Conditions/Review of Yesterday's Forecast:
The remnants of Gaston (PGI38L) continue to move through the
Caribbean. Ensemble track forecasts have been running a little
north of the actual position of the system, though the ensemble
has been consistent in not trying to redevelop a TS from this
pouch. The initial position of this system is slightly north of
the NHC defined position. The ensemble contains quite a bit of
variability associated with INVEST91 (PGI41L) at the initial
time, which is typical of an INVEST area. PGI39L has been
handled well by the ensemble. All members have showed this
system as very weak and the tracks have been fairly good.
PGI42L is outside the domain at the initial time again and is
not discussed.
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DAY 1 (Next 24 hours) Outlook:
The ensemble suggests that the center of ex-Gaston will be over
Hispaniola by 24 h. All ensemble members show little change in
both the circulation and thickness anomaly over this period.
INVEST91 has increasing circulation and thickness anomaly values
for all ensemble members. While the circulation value is
greater than genesis criteria, the thickness anomaly is smaller
at this point. The position variance is oriented E-W. PGI39L
shows decreasing circulation, thickness anomaly, and OW values
during this period. The position variance is fairly uniform in
the first 24 h.
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DAY 2 (24 - 48 hours) Outlook:
Gaston moves back over water and is located in between Cuba and
Jamaica. The position variance is fairly uniform in all
horizontal directions. In addition, there is a small increase
in circulation and thickness anomaly during this period, but all
members are below genesis criteria. By 48 h, nearly all
ensemble members exceed genesis criteria for both the
circulation and thickness anomaly. In addition, the ensemble
mean SLP is below 1000 hPa, which suggests this system has
undergone genesis. The position variance has taken a more SW-NE
orientation to it, with the stronger members more likely to be
to the west. PGI39L has circulation values at or near zero for
all ensemble members, thus the ensemble predicts this pouch will
be dissipated.
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Extended Outlook:
The ensemble shows more variability in Gaston's position by the
end of the period. While most members are south of Cuba, a few
members actually move across Jamaica and are significantly south
of the ensemble mean position. These members have minimum SLP
values below 1000 hPa, although the circulation and thickness
anomaly values are not much different. It appears that these
ensemble members get into an environment of lower shear compared
to the rest of the ensemble. All of the intensity metrics for
INVEST91 continue to increase, except for a single member. This
suggests the ensemble predicts this system will be a TS by the
end of this period. The position variance is fairly uniform in
all directions. There are no other systems of interest in the
forecast, except for what appears to be the consolidation of the
monsoon trough in the Atlantic basin into a coherent vortex.
The ensemble has tried to do this on numerous occasions this
season, so I am not inclined to believe this will actually
happen.
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PREDICT Synopsis: All ensembles show Gaston re-genesis in 48 hrs - JAC, 9/8/2010, 8:49 am Post A Reply
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