Hurricane Humberto Forecast Discussion

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WTNT44 KNHC 181444
TCDAT4

Hurricane Humberto Discussion Number  24
NWS National Hurricane Center Miami FL       AL092019
1100 AM AST Wed Sep 18 2019

An Air Force Reserve Hurricane Hunter aircraft conducting a
reconnoiter of Humberto this morning found that the intensity of the
major hurricane had increased slightly, but that the inner-core 64-
and 50-kt wind fields had expanded significantly, now extending
outward up to at least 90 n mi and 110 n mi, respectively, in the
southeastern quadrant. During their pass through the southeastern
quadrant, the aircraft measured 700-mb flight-level winds of 120 kt,
but peak SFMR winds of only 97 kt. Given that convection is minimal
in that quadrant, the normal downward mixing is likely not
occurring, the intensity has only been increased to 105 kt. The
aircraft also measured a central pressure of 952 mb with a
dropsonde, which is close to the pressure of 954.2 mb with 30-kt
winds that NOAA buoy 41048 measured in the eye around 0930 UTC.

The initial motion estimate remains 065/14 kt. Humberto is beginning
to feel the effects of a deep-layer trough approaching from the
west, and the hurricane should continue to accelerate toward the
east-northeast through tonight, passing just north and northwest
of Bermuda, followed by a turn toward the northeast by early
Thursday afternoon. By 48 hours or so, Humberto is forecast to turn
back toward the east-northeast and maintain that motion through day
5 as a ridge to the east of the cyclone weakens and flattens out.
The new NHC track forecast is very similar to the previous one for
the first 36 hours, and then is a little faster and to the left of
the previous advisory thereafter, closer to the tightly packed
consensus track model guidance.

Humberto may have peaked in intensity based on the cloud pattern
in satellite imagery beginning to take on the appearance of an
extratropical cyclone. Thus, some fluctuations in strength could
occur during the next 12 hours or so. Thereafter, very strong
southwesterly vertical wind shear and cold upwelling beneath the
hurricane should disrupt the inner-core convection and organization,
resulting in steady weakening. By 72 hours, the global models
continue to show Humberto merging with a frontal system, and the
NHC intensity forecast calls for extratropical transition by that
time. The official intensity forecast follows the corrected-
consensus models HCCA and FSSE through the next 12-24 hours, and
then is above that guidance through the remainder of the forecast
period, closer to an average of the global models.

Key Messages:

1. A prolonged period of dangerous winds is expected on Bermuda from
late this afternoon through Thursday morning, with hurricane-force
winds expected overnight tonight. 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  18/1500Z 32.2N  68.1W  105 KT 120 MPH
 12H  19/0000Z 33.5N  65.4W  100 KT 115 MPH
 24H  19/1200Z 36.1N  62.1W   90 KT 105 MPH
 36H  20/0000Z 38.6N  60.5W   75 KT  85 MPH
 48H  20/1200Z 40.7N  59.5W   60 KT  70 MPH
 72H  21/1200Z 43.3N  50.4W   45 KT  50 MPH...POST-TROP/EXTRATROP
 96H  22/1200Z 47.2N  33.4W   45 KT  50 MPH...POST-TROP/EXTRATROP
120H  23/1200Z 54.0N  20.0W   45 KT  50 MPH...POST-TROP/EXTRATROP

$$
Forecaster Stewart



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