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Hurricane Humberto Forecast Discussion


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043 
WTNT44 KNHC 161450
TCDAT4

Hurricane Humberto Discussion Number  16
NWS National Hurricane Center Miami FL       AL092019
1100 AM EDT Mon Sep 16 2019

An Air Force Reserve reconnaissance aircraft investigating Humberto
this morning found peak 850-mb flight-level winds of 88 kt in the
southeastern and northeastern quadrants, along with SFMR surface
winds of 72-73 kt in the northeastern quadrant and a minimum
pressure of 978 mb. These data support an intensity of 75 kt.

The initial motion estimate is east-northeastward or 070/06 kt.
Humberto is now solidly located north of the Bermuda-Azores ridge
axis, and a continued east-northeastward motion is expected for the
48 hours or so. Thereafter, a large deep-layer trough is forecast to
dig southward out of Atlantic Canada and the Canadian Maritimes to
the west of Humberto, forcing the hurricane to gradually lift out
to the northeast. The exact timing that the trough begins to affect
Humberto's motion will be critical in determining how close the
hurricane will come to Bermuda.  The latest model guidance is in
better agreement and more tightly packed than previous runs,
suggesting that the poleward turn will occur at least 100 n mi west
of the island. By days 4 and 5, however, the model guidance becomes
strongly divergent with a large spread of about 1000 n mi on day 5,
resulting in lower-than-normal confidence in the track forecast on
those days. The new NHC track foreast was nudged only slightly
southward through 48 hours, and lies close to a blend of the
consensus models TVCN, NOAA-HCCA, and FSSE.

Humberto has been strengthening at a rate of 20 kt per 24 hours
since this time yesterday, and that trend is expected to continue
for the next day or so given the warm water beneath the hurricane
and a continued favorable upper-level outflow pattern. The hurricane
is expected to peak as a major hurricane in 36-48 hours when the
cyclone will be located over SSTs of about 29 deg C and moving into
the right-rear quadrant of a strong upper-level jet maximum.
Thereafter, strong southwesterly vertical wind shear is expected to
gradually diminish convection around the center despite the
impressive baroclinic/dynamically driven pressure falls, which will
mainly act to spread out the surface wind field rather than
intensify the cyclone. Humberto is forecast to interact with an
approaching cold front on day 5, resulting in extratropical
transition over the colder Atlantic waters north of the Gulf Stream.
The official intensity forecast is just an update of the previous
advisory and now shows Humberto reaching major hurricane status,
similar to the HCCA, FSSE, and HWRF models. Since Humberto's wind
field is expected to expand significantly by day 2, a Tropical
Storm Watch for Bermuda will likely be required on the 500 pm EDT
advisory.

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  16/1500Z 29.9N  76.5W   75 KT  85 MPH
 12H  17/0000Z 30.1N  75.6W   85 KT 100 MPH
 24H  17/1200Z 30.4N  74.4W   95 KT 110 MPH
 36H  18/0000Z 30.7N  72.7W  100 KT 115 MPH
 48H  18/1200Z 31.3N  70.5W   95 KT 110 MPH
 72H  19/1200Z 33.7N  65.0W   85 KT 100 MPH
 96H  20/1200Z 37.9N  60.9W   70 KT  80 MPH
120H  21/1200Z 40.8N  56.8W   60 KT  70 MPH...POST-TROP/EXTRATROP

$$
Forecaster Stewart