[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 101457
TCDAT2

Potential Tropical Cyclone Two Discussion Number   1
NWS National Hurricane Center Miami FL       AL022019
1000 AM CDT Wed Jul 10 2019

High-resolution satellite imagery along with surface and upper-air
data indicate that the broad low pressure system located over the
northeastern Gulf of Mexico has become a little better defined. The
initial intensity of 25 kt is based on an average of 1-minute wind
speeds of 20-33 kt reported by ships and buoys well south of the
poorly defined center. Although the system is currently experiencing
some northerly vertical wind shear, the shear is expected to
gradually subside over the next day or so, and the low has a high
chance of becoming a tropical depression or tropical storm by
Thursday. Since this system has the potential to bring tropical
storm conditions and storm surge to portions of the coast of
Louisiana by late Thursday or Friday, Potential Tropical Cyclone
advisories are being initiated at this time.

The initial motion estimate is an uncertain 245/07 kt. Some erratic
motion will be possible during the 24 hours or until a well-defined
center develops. However, the general motion as indicated by the
global and regional models is expected to be toward the west-
southwest or southwest. By Friday, the cyclone is forecast to turn
toward the west-northwest and then turn northwestward by Saturday
into a developing break in a deep-layer ridge that currently extends
from the southeastern U.S. westward across the southern Plains and
into the Desert Southwest. The timing of the ridge breakdown owing
to a shortwave trough moving southeastward out of the northern
Plains will be critical since a later/earlier turn by the cyclone
would shift the track west/east of the current forecast. The model
guidance is widely divergent after 48 hours with the UKMET model the
farthest west showing landfall along the Upper Texas coast, and the
GFS and HMON models farther east with landfall in south-central
Louisiana. The ECMWF model is about midway between these two
extremes, and the official track forecast leans toward that
model since it has performed well during this system's
pre-development phase.  Note that forecast uncertainty for
disturbances is generally larger than for tropical cyclones,
especially beyond 48-72 hours.

Only slow strengthening is expected for the next 24-36 hours due to
the lack of a well-defined center and inner-core wind field, along
with some modest northerly wind shear. By 48 hours and beyond,
however, the combination of atmospheric and oceanic conditions
become ideal for intensification. The very low shear shear
conditions, an impressive outflow pattern forecast by all of the
global and regional models, and anomalously warm sea-surface
temperatures of 30-31C argue for quick intensification, but given
that the system is still in the formative stages, the official
intensity forecast is a little below IVCN consensus through 48
hours and trends higher toward the ECMWF-based SHIPS guidance at
72 hours.

Key Messages:

1. A tropical depression is expected to form later today or
Thursday. Conditions appear favorable for this system to strengthen
to a hurricane at it approaches the central Gulf Coast by the
weekend.

2. Dangerous storm surge is possible in portions of southeast
Louisiana, and a Storm Surge Watch has been issued for this area.
The risk for dangerous storm surge impacts also exists farther west
along the Louisiana coast into the Upper Texas coast, and additional
storm surge watches may be needed later today or tonight. Residents
in these areas should monitor the progress of this system and listen
to any advice given by local officials.

3. A Tropical Storm Watch has been issued for portions of the
Louisiana coast and additional Tropical Storm or Hurricane Watches
could be needed later today or tonight for the remainder of the
Louisiana coast and the Upper Texas Coast.

4. The system has the potential to produce very heavy rainfall along
and inland of the central Gulf Coast through early next week. For
more information, see products from your local National Weather
Service office and the NOAA Weather Prediction Center.

FORECAST POSITIONS AND MAX WINDS

INIT  10/1500Z 28.5N  86.4W   25 KT  30 MPH...POTENTIAL TROP CYCLONE
 12H  11/0000Z 27.9N  87.3W   25 KT  30 MPH...POTENTIAL TROP CYCLONE
 24H  11/1200Z 27.5N  88.2W   30 KT  35 MPH...TROPICAL DEPRESSION
 36H  12/0000Z 27.4N  89.3W   40 KT  45 MPH
 48H  12/1200Z 27.6N  90.4W   50 KT  60 MPH
 72H  13/1200Z 28.7N  92.3W   75 KT  85 MPH
 96H  14/1200Z 30.7N  93.0W   65 KT  75 MPH...INLAND
120H  15/1200Z 32.6N  94.1W   30 KT  35 MPH...INLAND

$$
Forecaster Stewart

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