000
WTNT42 KNHC 080252
TCDAT2

TROPICAL STORM GRACE DISCUSSION NUMBER  11
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL072015
1100 PM AST MON SEP 07 2015

After being devoid of any significant convection near the center for
almost 6 hours, a small burst of deep convection with cloud tops
colder than -80 deg C has developed since 0000 UTC just south of and
over the previously exposed low-level circulation center. This
recent convective development is the reason for keeping Grace as a
35-kt tropical storm. This intensity is supported by a Dvorak
current intensity estimate of T2.5/35 kt from TAFB and a couple of
32-kt ASCAT-B wind vectors.

The initial motion estimate is 275/17 kt. There is essentially no
change to the previous forecast reasonings over the past couple of
days. Grace is expected to gradually weaken and become more
vertically shallow, and be steered quickly westward by the moderate
low-level easterly trade wind flow on the south side of a deep-layer
ridge. The official track forecast is just an update and extension
of the previous advisory track, and lies close to the dynamical
model consensus, TVCA.

With increasing southwesterly to westerly vertical wind shear and an
abundance of dry mid-level air ahead of Grace, steady weakening is
expected due to these hostile environmental conditions. The only
saving grace is the cyclone's robust low-level circulation, which
could force periodic bursts of deep convection for the next 24 hours
or so, similar to the most recent convective development. However,
by 36 hours and beyond, westerly shear in excess of 25 kt should
cause the circulation to weaken significantly due to less frequent
and shorter duration convective bursts. Degeneration into a remnant
low is expected by 48 hours, followed by dissipation in 96 hours.
However, dissipation could occur sooner, similar to the ECMWF model
solution. The new NHC intensity forecast closely follows the IVCN
consensus model.

FORECAST POSITIONS AND MAX WINDS

INIT  08/0300Z 14.0N  39.2W   35 KT  40 MPH
 12H  08/1200Z 14.1N  41.8W   35 KT  40 MPH
 24H  09/0000Z 14.3N  45.1W   30 KT  35 MPH
 36H  09/1200Z 14.7N  48.4W   30 KT  35 MPH
 48H  10/0000Z 15.1N  51.8W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  11/0000Z 16.0N  58.8W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  12/0000Z...DISSIPATED

$$
Forecaster Stewart