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Hurricane Humberto Forecast Discussion


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000
WTNT44 KNHC 182052
TCDAT4

Hurricane Humberto Discussion Number  25
NWS National Hurricane Center Miami FL       AL092019
500 PM AST Wed Sep 18 2019

Normal communications with the Bermuda Weather Service have been
disrupted due to a lightning strike.

Humberto is taking on more of a hybrid-extratropical structure based
on most of the rain shield having been displaced to the left or
poleward side of the circulation now as seen in Bermuda weather
radar data, and also in conventional and passive microwave satellite
imagery. Sustained hurricane-force winds and gusts have been
measured by amateur radio operators across the island, with a peak
gust to 104 mph having been reported thus far at Ports Island,
Bermuda. The initial intensity of 105 kt on the previous advisory
has been maintained since little overall change in the structure has
occurred since the last aircraft reconnaissance mission 6 hours ago.

The initial motion estimate is 060/17 kt. There are no significant
changes to the previous forecast track or reasoning. Humberto has
basically remained on track during the past 24 hours. The hurricane
is expected to continue accelerating toward the east-northeast
tonight and Thursday morning, with the center expected to pass
about 80 nmi northwest of Bermuda early this evening. A turn toward
the northeast and north-northeast is forecast to occur by early
Thursday afternoon, followed by a motion toward the east-northeast
by 48 hours, with the latter motion continuing through 96 hours. The
new official track forecast is similar to the previous advisory
track, and lies close to the tightly packed TVCN, NOAA-HCCA, and
FSSE consensus track models.

Humberto is now fully embedded within an anticyclonically curved
right-rear jet entrance region. As a result, some fluctuations in
strength could occur during the next 12 hours or so. Thereafter,
strong southwesterly vertical wind shear in excess of 50 kt, along
with cold upwelling beneath the hurricane, should combine to induce
steady weakening. By 48 hours, the global models continue to
forecast Humberto to merge with a frontal system, and the NHC
intensity forecast calls for extratropical transition around that
time. The official intensity forecast follows an average of the
global models' intensity forecasts due to Humberto's hybrid nature,
which is not being captured properly by the tropical-cyclone-based
consensus intensity models.

Key Messages:

1. A prolonged period of dangerous winds is expected to continue on
Bermuda through Thursday morning, with hurricane-force winds
expected during the next several hours. Preparations to protect
life and property should be rushed to completion.

2. Storm surge and dangerous breaking waves could cause coastal
flooding tonight and Thursday along the southern coast of Bermuda.

3. Swells will continue to affect the northwestern Bahamas and the
southeastern coast of the United States from east-central Florida to
North Carolina during the next couple of days, creating life-
threatening surf and rip current conditions.

FORECAST POSITIONS AND MAX WINDS

INIT  18/2100Z 33.0N  66.3W  105 KT 120 MPH
 12H  19/0600Z 34.6N  63.6W  105 KT 120 MPH
 24H  19/1800Z 37.4N  61.0W   95 KT 110 MPH
 36H  20/0600Z 39.8N  60.0W   75 KT  85 MPH
 48H  20/1800Z 41.6N  58.7W   60 KT  70 MPH...POST-TROP/EXTRATROP
 72H  21/1800Z 43.9N  47.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
 96H  22/1800Z 49.0N  30.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
120H  23/1800Z...DISSIPATED/ABSORBED

$$
Forecaster Stewart