Re: 31L is what GFS is developing as a cane
Posted by JAC on 8/17/2010, 12:22 pm
Date (UTC): 2010/08/17 15:22
Author: Boothe
Submitted at (UTC): 2010/08/17 15:42
Revised at(UTC): 2010/08/17 15:55
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Pouch Name: PGI31L        Official Name:        Initial Center Point: 13N   33W
Notes:

WORD OF CAUTION!
I don't usually initiate a pouch that is developing in the
horizontal shear zone in the middle of the Atlantic; however,
the models not only develop a pouch that interacts with nearby
PGI30L, but also ends up more intense than PGI30L.

Although PGI31L is intense at the end of the forecast in most
models, it is not at analysis, and determining its initial
position is troublesome.  THERE IS A HIGH AMOUNT OF UNCERTAINTY
IN THE FIRST 24 HOURS FOR THE POSITIONS.  Essentially, a large
circulation ~35W is apparent in the analysis.  I did position
PGI31L in that large circulation in GFS; however, it becomes
fairly apparent that while that large circulation actually
weakens and creeps westward, a cyclonic area to the east is what
develops.  So, some of the models appear to jump to the east for
that reason.  (In hindsight, I probably should have initiated
PGI31L farther east.)

That being said, the models (except NOGAPS) do indicate a bit of
eastward motion in the beginning during a Fujiwhara with PGI30L,
followed by westward motion.  For that reason, I simply used a
PHASE SPEED OF ZERO m/s.


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ECMWF:  Phase Speed:        Determination:        Level tracked:

I did not put positions on the larger, weak circulation to the
west (which I thought would be the initial position) ... only
the smaller circulation to the east that later develops.  For
that reason, the map is shifted too far west, and the developing
PGI31L is off the eastern edge of the map.


GFS:      Phase Speed:        Determination:        Level tracked:

I put the initial position on the larger, weak circulation to
the west (~35W), but then I jump to the rapidly developing
system to the east; hence the unrealistic jump to the east.
PGI31L becomes more intense than PGI30L by the end of the
forecast.


UKMET:  Phase Speed:        Determination:        Level tracked:

Similar to GFS.


NOGAPS:  Phase Speed:        Determination:        Level tracked:

Here is where I got really inconsistent!  I tracked only the
weaker western circulation, which creeps westward and quickly
dissipates.  However, there's a reason.  Although NOGAPS does
develop a non-PGI30L pouch, it is much farther east ... east of
PGI30L (see the fields for PGI30L).  I'm not sure if it is
simply an ITCZ development or the next wave coming off of
Africa, but I am sure that I could not jump PGI31L THAT FAR
east!
88
In this thread:
30L Hits the Water with a very-strong Moisture Column - JAC, 8/16/2010, 4:06 pm
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