Tuesday, June 20, 2017


WTNT42 KNHC 200853

Tropical Storm Bret Discussion Number   7
NWS National Hurricane Center Miami FL       AL022017
500 AM AST Tue Jun 20 2017

Bret continues to have a fairly well-organized appearance on
satellite imagery, but the presentation on radar from Trinidad and
Venezuela is not so impressive, with a lack of well-defined banding
features.  The structure of the cyclone continues to be
characterized by a northward tilt of the vortex with height, so
the center is estimated to be located near the southern side of the
CDO.  The initial intensity is held at 35 kt for this advisory,
which is the mean of Dvorak T-numbers from SAB and TAFB.  The
intensity forecast reasoning remains about the same as before.  No
significant short-term strengthening seems likely while the
circulation interacts with Venezuela today.  In 24 hours or so, a
weakening trend should commence due to strong south-southwesterly
shear associated with an upper-level trough over the Caribbean Sea.
The global models continue to be in good agreement that the system
will dissipate over the west-central Caribbean in 2-3 days.  The
official intensity forecast is near or slightly above the intensity
model consensus, IVCN.

The forward motion has slowed just a bit from yesterday and is now
around 290/18 kt.  There continues to be little change to the track
forecast philosophy.  The flow on the southern side of a
well-defined mid-level subtropical ridge should steer the cyclone on
a west-northwestward to westward track for the next couple of days.
The official track forecast lies between the latest ECMWF and GFS
solutions and is close to the model consensus.


INIT  20/0900Z 10.6N  62.9W   35 KT  40 MPH
 12H  20/1800Z 11.5N  65.3W   35 KT  40 MPH
 24H  21/0600Z 12.4N  68.7W   35 KT  40 MPH
 36H  21/1800Z 13.3N  72.7W   30 KT  35 MPH
 48H  22/0600Z 13.6N  76.7W   30 KT  35 MPH...POST-TROP/REMNT LOW
 72H  23/0600Z...DISSIPATED

Forecaster Pasch 

WTNT43 KNHC 200852

Potential Tropical Cyclone Three Discussion Number   3
NWS National Hurricane Center Miami FL       AL032017
400 AM CDT Tue Jun 20 2017

Nighttime infrared satellite imagery suggests that the circulation
associated with the low pressure area in the Gulf of Mexico is
gradually becoming better defined.  However, the system is
struggling to maintain organized convection near the center, and
the radius of maximum winds remains large.  Based on this, the
system is still maintained as a potential tropical cyclone.

The low is moving erratically northwestward around the southwestern
portion of a deep-layer ridge located over the western Atlantic and
Florida.  The large-scale models suggest this ridge will strengthen
some during the next 36 hours or so and cause the low to turn a
little more westward.  This would be followed by a northward turn
around the western end of the ridge and eventual recurvature into
the westerlies.  Overall, there has been a left shift of the track
guidance models since the previous advisory.  The new forecast
track is also shifted left, but it is to the right of the model
consensus, especially at 36-48 h.  Given the nature of the
circulation, though, and the fact that the wind and rain hazards
extend well north and east of the center, users are encouraged to
not focus on the details of the track forecast.

The initial intensity remains 35 kt based on partial scatterometer
overpasses and continuity from the previous advisory.  Significant
strengthening is unlikely due to strong vertical shear caused by an
upper-level trough over the northwestern Gulf of Mexico and
entrainment of dry air into the system.  However, the large-scale
models suggest slight strengthening before landfall, and thus the
intensity forecast is unchanged from the previous advisory.  One
change from the previous advisory is that it now appears more
likely that the system would become a subtropical cyclone than a
tropical cyclone due to the current structure of the low and
interaction with the aforementioned trough.  That being said,
development into a tropical cyclone remains possible.

The primary hazard from this disturbance is expected to be heavy
rainfall over portions of the central and eastern Gulf Coast.


INIT  20/0900Z 24.8N  90.1W   35 KT  40 MPH...POTENTIAL TROP CYCLONE
 12H  20/1800Z 25.7N  91.0W   35 KT  40 MPH...SUBTROPICAL CYCLONE
 24H  21/0600Z 26.6N  92.1W   40 KT  45 MPH
 36H  21/1800Z 27.5N  93.0W   40 KT  45 MPH
 48H  22/0600Z 28.9N  93.5W   40 KT  45 MPH
 72H  23/0600Z 32.5N  93.5W   25 KT  30 MPH...INLAND
 96H  24/0600Z 36.5N  88.0W   20 KT  25 MPH...POST-TROP/INLAND
120H  25/0600Z...DISSIPATED

Forecaster Beven 


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