NHC - Gaston A Cat 2 In 3.5 Days
Posted by DougInBrevardForce10 on 9/2/2010, 2:03 am


Gaston has maintained a well-defined curved band of convection that
wraps from the western to northern sides of the circulation...and
Dvorak final-T numbers are t2.5/35 kt from both TAFB and SAB.  The
objective ADT estimate from UW-CIMSS is currently t3.3/51 kt...but
a recent 0013 UTC ascat pass shows winds no higher than 25-30 kt.
The initial intensity is kept at 35 kt as a blend of these
estimates.


The official intensity forecast has again been increased a bit from
the previous advisory.  Although there is some dry air surrounding
the cyclone...global model guidance suggests that the vertical
shear should remain low...at least for the next 2-3 days...and this
could prevent the dry air from having a significant effect.
Still...there is a lot of uncertainty in the intensity forecast
given the differences between the dynamical and statistical models.
Over the next 5 days...the GFDL and HWRF only strengthen Gaston to
a strong tropical storm or minimal hurricane...the SHIPS model
makes it a category 2 hurricane...and the lgem brings it to
category 4 intensity.  The official forecast is a little above the
intensity consensus for the first 48 hours when environmental
conditions should be most ideal and then very close to the
consensus thereafter when easterly shear could increase a bit.


The latest satellite fixes indicate that Gaston has begun to slow
down...possibly due to a mid-level trough located to its
northwest.  It is also a little farther north than previously
estimated and has an initial motion of 280/10 kt.  With the break
in the subtropical ridge...Gaston is expected to continue to
slow down over the next couple of days.  The multi-model consensus
tvcn is slower than the previous forecast...so the new official
forecast shows a slower motion over the next 36 hours...but is
still on the same general track as the previous advisory.  By days
4 and 5...the ridge is expected to strengthen...and the cyclone
should begin to move faster to the west.
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NHC - Gaston A Cat 2 In 3.5 Days - DougInBrevardForce10, 9/2/2010, 2:03 am
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