11 A.M. DISCUSSION: NICK'S CENTER........

[dixiebreeze]

center still somewhat exposed SW:

Tropical Storm Nicholas Discussion Number 16


Statement as of 11:00 am EDT on October 17, 2003



satellite imagery shows that Nicholas is slowly organizing...with a
central dense overcast and some outer banding in the eastern
semicircle. However...an SSM/I overpass at 0952z showed linear
convection in the overcast and a low-level center exposed south of
the convection. Satellite intensity estimates have unanimously
increased to 65 kt. Given the microwave data...Nicholas will
remain a tropical storm at this time with 60 kt maximum winds.
The initial motion is a somewhat uncertain 320/8. Visible imagery
and surface observations indicate a weak low/mid-level ridge north
of Nicholas. Water vapor imagery shows a broad upper-level ridge
along 41w/42w S of 22n...and a stream of shortwave troughs and
ridges in the westerlies N of 21n W of 44w. This complex pattern
is producing weak steering currents...and the track guidance
responds to this by generally forecasting a slow northwestward or
north-northwestward motion. There is better agreement between the
dynamical models than 24 hr ago...as the NOGAPS has shifted
westward from its previous forecasts. However...there are still
outliers such as the eastward LBAR and the westward BAMS. The
forecast track calls for a slow northwestward motion down the
middle of the guidance envelope...and is nudged a little to the
right of the previous package.

The upper-level ridge southeast of Nicholas has a well-defined wind
maximum along its northern periphery. This wind band is currently
close to Nicholas and is causing southwesterly shear. The future
intensity depends on how close the storm stays to the wind maximum.
Dynamical models forecast the ridge to move westward...which could
force the wind maximum north of the cyclone and create a more
favorable environment during the next 48 hr...especially if
Nicholas moves slower than forecast. Conversely...if the storm
moves faster than forecast...it would remain in stronger shear.
The SHIPS model calls for steady weakening through the forecast
period under moderate to strong shear...which seemingly does not
match either current trends or the model upper-level winds
forecasts. The low-confidence intensity forecast calls for a
little more strengthening in anticipation of some decrease in the
shear...followed by weakening after 48 hr as Nicholas encounters
stronger westerlies along and north of 20n.
Forecaster Beven