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Tropical Storm Humberto Discussion Number  12
NWS National Hurricane Center Miami FL       AL092019
1100 AM EDT Sun Sep 15 2019

Visible and passive microwave satellite imagery indicate that
Humberto's inner-core region has improved markedly since early this
morning, including the development of a small but ragged mid-level
eye. In addition, significant dry air entrainment that has been
plaguing the cyclone since its formation appears to have abated
based on the recent development of deep convection in the dry slot
located in the southern semicircle of Humberto's circulation.
Anticyclonic outflow has also been increasing in all quadrants,
along with a hint of cloud-filled eye in recent visible imagery.
Buoy 41010 located just west of the center recently reported a
pressure of 1001.8 mb and 41-kt winds at 4-meters elevation. The
initial intensity has been increased to 55 kt based on a Dvorak
intensity estimate of T3.5/55 kt from TAFB. AN Air Force Reserve
reconnaissance aircraft will reconnoiter Humberto this afternoon,
providing more detailed information on the cyclone's intensity.

The initial motion estimate is 350/06 kt, based mainly on microwave
satellite fix positions. NHC model guidance remains in excellent
agreement on Humberto moving slowly northward through a break in the
subtropical ridge today and tonight, then making a sharp turn toward
the northeast on Monday when the cyclone passes north of the narrow
east-west oriented ridge axis. On days 2-5, the tropical cyclone is
forecast to gradually accelerate toward the northeast and
east-northeast under the influence of increasing westerlies ahead of
a deepening mid-latitude trough forecast to dig southeastward out of
Canada and into the extreme northwestern Atlantic Ocean. The new
official forecast track is very similar to the previous advisory
track, and lies close to a blend of the tightly packed consensus
track models.

Humberto now appears to be well on its way to becoming a hurricane
fairly soon based on the newly formed central dense overcast and
mid-level eye feature. Although the large-scale shear is fairly
large in the SHIPS intensity models, the shear directly over the
center of Humberto is forecast to remain low for the next 48 hours
or so, which should allow for steady strengthening. By 72 hours, the
cyclone is forecast to be situated in the right-rear quadrant of a
strong, anticyclonically curved jet maximum. The associated
upper-level divergence is expected to induce strong pressure falls
and strengthening despite the vertical shear increasing to more than
30 kt. By 96 hours and beyond, slightly cooler waters, much drier
air, and very hostile shear conditions of more than 40 kt should
cause steady weakening. The new NHC intensity forecast follows the
trend of the previous advisory, but now shows Humberto reaching peak
intensity in 72 hours, coincident with the warmest water
temperatures of about 29C and greatest jetstream dynamical forcing.

Large swells from Humberto will affect portions of the northwestern
Bahamas and southeastern United States coast during the next few
days.  These swells are expected to produce dangerous surf
conditions and life-threatening rip currents.  See products issued
by your local weather office for additional information.

FORECAST POSITIONS AND MAX WINDS

INIT  15/1500Z 28.9N  77.9W   55 KT  65 MPH
 12H  16/0000Z 29.5N  77.7W   65 KT  75 MPH
 24H  16/1200Z 30.0N  77.1W   70 KT  80 MPH
 36H  17/0000Z 30.3N  75.9W   80 KT  90 MPH
 48H  17/1200Z 30.7N  74.4W   85 KT 100 MPH
 72H  18/1200Z 31.6N  69.6W   95 KT 110 MPH
 96H  19/1200Z 34.5N  62.8W   85 KT 100 MPH
120H  20/1200Z 39.0N  57.0W   65 KT  75 MPH

$$
Forecaster Stewart

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