PREDICT's Ensemble Discussion --> Weak development and slow moving next 48 hrs
Posted by JAC on 8/19/2010, 9:25 am
PREDICT Ensemble Discussion

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Date(UTC): 2010/08/19 11:35
Author: Ryan Torn
Submitted at(UTC): 2010/08/19 12:01
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Current Conditions/Review of Yesterday's Forecast:
**** Due to computer problems at NCAR, there was no 0000 UTC
run, thus the discussion pertains to the 1200 UTC forecast from
yesterday.

PGI27L moving to western Caribbean.  This system is still not
considered in INVEST area by NHC, thus the forecasts of minimal
strengthening are accurate.  PGI30L still distinct from PGI31L.
As in PGI27L, no members have OW values greater than 2.  PGI31L
shows up as a large region of vorticity.  Only about 20% of the
ensemble members have OW values greater than 2 for this system.
PGI32L appears to be initialized too far SW of the analyzed
position.  PGI33L is coming through the lateral boundaries of
the model.

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DAY 1 (Next 24 hours) Outlook:
Although there is a great deal of spread in the timing, PGI27L
makes landfall around Belize without any change in intensity.
PGI30L weakens as it moves to the west and is difficult to track
in most members beyond 0000 UTC 20 August. PGI31L goes from
having an elongated region of vorticity to a more circular
orientation.  At the same time, the number of members with OW
values greater than 2 increases to around 45% of the ensemble.
As with the analysis, there is a great deal of spread in the
position of PGI32L, but no hint at development.  PGI33L moves
off the African coast, but is not characterized by OW values
greater than 2.

Finally, the tail end of the tropical trough north of the ITCZ
appears to roll up and become a compact circulation center.  By
this time, 25% of the ensemble members have OW values greater
than 2.  This development has been in the ensemble forecasts for
the past 3 initialization times that have run; however, this
does not appear in many operational forecasts. It is not clear
why the ensemble is so aggressive with this system.  Currently,
there is some convection off the South American coast where this
system is to develop, but it does not look like it will happen
immediately.  I am weary that this system might be a spurious
development.

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DAY 2 (24 - 48 hours) Outlook:
PGI27L and PGI30L difficult to track.  PGI31L still remains
around 30W, where roughly 50% of members have OW values greater
than 2.  No signs of change in the total circulation of the
system.  PGI32L still characterized by large variability in
position, but no OW values greater than 2.  PGI33L makes little
progress moving off African coast, though roughly 20% of members
have OW values greater than 2. Finally, the potentially
spurious development SE of the leeward islands strengthens as it
moves to the NW.  60% of the members have OW values greater than
2.

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Extended Outlook:
PGI31L starts to slowly move westward without much change in
intensity.  PGI32L difficult to track, though it appears that it
merges with the potentially spurious system.  PGI33L has moved
little and appears to have a similar intensity.  The potentially
spurious system should be moving over the islands at this point.
Based on circulation values, this system is likely a TD by this
point.
83
In this thread:
31L Looks Good to Go - JAC, 8/19/2010, 7:08 am
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