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Tropical Storm Barbara Discussion Number   3
NWS National Hurricane Center Miami FL       EP022019
900 PM MDT Sun Jun 30 2019

Barbara has continued to strengthen despite modest northwesterly
mid-level vertical wind shear that has been undercutting a rapidly
improving upper-level outflow pattern. Passive microwave satellite
images over the past few hours indicate that the low-level center is
displaced to the west of the coldest overshooting tops due to the
aforementioned shear conditions. The initial intensity has been
increased to 45 kt based on a consensus Dvorak intensity of T3.0/45
from TAFB and SAB, which is consistent with a late-arriving 1647Z
ASCAT-C overpass that contained wind vectors of 41-42 kt.

The initial motion is an unusually brisk 275/19 kt.  A deep-layer
ridge to the north of Barbara is expected to steer the tropical
cyclone westward to west-northwestward for the next 48-72 hours,
accompanied by a gradual decrease in forward speed. By 96 hours, a
shortwave trough is forecast to weaken the ridge, allowing Barbara
to turn more toward the northwest and gain some latitude. By day 5,
however, the ridge is forecast to build back in behind the exiting
trough, which should force the cyclone back on a west-northwesterly
to westerly track. The latest track guidance continues to be tightly
clustered with the HWRF remaining on the north side of the envelope
and the ECMWF on the south side. The new NHC track forecast is
similar to but a little south of the previous advisory track, and
lies close to a blend of the TVCE, HCCA, and FSSE consensus models.

The global models continue to forecast the deep-layer and mid-level
vertical wind shear to steadily decrease from the current 15 kt to
near 5 kt by 48-72 hours. The low shear conditions, along with SSTs
of 28-29 deg C, should allow for at least steady strengthening for
the next 48 h or so, followed by more significant strengthening in
the 48-72 h time period. After that time, cooler water temperatures
beneath the cyclone coupled with the strong inner-core wind field
are expected to result in significant cold upwelling, which should
induce steady weakening on days 4-5. Rapid intensification in the
24-72 h time frame is a distinct possibility, which would result in
Barbara becoming a stronger major hurricane than currently forecast.
The new official intensity forecast is a little more robust than the
previous advisory, and follows a blend of the HCCA, ICON, and FSSE
intensity consensus models.

FORECAST POSITIONS AND MAX WINDS

INIT  01/0300Z 11.0N 114.2W   45 KT  50 MPH
 12H  01/1200Z 11.5N 116.3W   55 KT  65 MPH
 24H  02/0000Z 11.9N 119.0W   65 KT  75 MPH
 36H  02/1200Z 12.3N 121.4W   75 KT  85 MPH
 48H  03/0000Z 12.8N 123.5W   90 KT 105 MPH
 72H  04/0000Z 14.0N 127.0W  105 KT 120 MPH
 96H  05/0000Z 15.7N 130.7W   90 KT 105 MPH
120H  06/0000Z 16.8N 135.0W   75 KT  85 MPH

$$
Forecaster Stewart

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