000
WTPZ41 KNHC 010832
TCDEP1

Tropical Storm Juliette Discussion Number   1
NWS National Hurricane Center Miami FL       EP112019
300 AM MDT Sun Sep 01 2019

Earlier scatterometer surface wind data around 0400 UTC indicate
that the low pressure system located about 400 nmi south-southwest
of Manzanillo, Mexico, had become better defined and that
tropical-storm-force winds were occurring in the northern
semicircle. More specifically, an ASCAT-A pass revealed peak surface
winds of 42 kt, which could have been slightly rain inflated, and an
ASCAT-C pass showed peak winds of 39 kt. Based on a blend of
these wind data, the low has been upgraded to a 40-kt tropical
storm, the tenth tropical storm of the 2019 eastern North Pacific
hurricane season.

Juliette's initial motion estimate is an uncertain 310/06 kt. The
advisory position is an average of the locations of the mid- and
low-level circulation centers, in anticipation of the low-level
center noted in the ASCAT-C wind data developing closer to the
recent bursts of central deep convection. Otherwise, the track
forecast is pretty straight-forward with the NHC model guidance in
good agreement on maintaining the deep-layer ridge to the north of
Juliette throughout the forecast period. This steering pattern
should result in the cyclone moving slowly northwestward today,
followed by a turn toward the west-northwest with an increase in
forward speed on Monday, with a west-northwestward motion continuing
through 120 hours. The NHC forecast track lies close to the tightly
packed consensus models HCCA and TVCE.

Juliette is expected to remain within a favorable environment for
intensification to occur over the next 48-72 hours or so, which is
characterized by low vertical wind shear of less than 10 kt, a
moist mid-level environment, and sea-surface temperatures (SST) of
28-29 deg C. Therefore, the official intensity forecast calls for
steady strengthening, with Juliette expected to become a hurricane
on Monday. By 96 hours, the cyclone will be moving over SSTs around
26 deg C and cooler, which should induce gradual weakening. The NHC
intensity forecast is above the consensus intensity models HCCA and
IVCN, and is close to a blend of the statistical SHIPS intensity
models and the dynamical HWRF model.

FORECAST POSITIONS AND MAX WINDS

INIT  01/0900Z 13.2N 107.6W   40 KT  45 MPH
 12H  01/1800Z 14.5N 109.4W   45 KT  50 MPH
 24H  02/0600Z 15.7N 111.5W   55 KT  65 MPH
 36H  02/1800Z 16.7N 113.5W   65 KT  75 MPH
 48H  03/0600Z 17.6N 115.2W   75 KT  85 MPH
 72H  04/0600Z 18.9N 118.0W   75 KT  85 MPH
 96H  05/0600Z 20.0N 121.0W   70 KT  80 MPH
120H  06/0600Z 21.8N 124.8W   55 KT  65 MPH

$$
Forecaster Stewart