Tropical Storm Humberto Forecast Discussion Number 6

By | September 14, 2019

Issued at 1100 PM EDT Fri Sep 13 2019

000
WTNT44 KNHC 140300 CCA
TCDAT4
Tropical Storm Humberto Discussion Number   6...Corrected
NWS National Hurricane Center Miami FL       AL092019
1100 PM EDT Fri Sep 13 2019
Corrected to change depression to storm in the second paragraph
Deep convection has been gradually increasing this evening, and it
is currently most organized in a curved band to the east of the
estimated center.  In addition, data from the NOAA Hurricane Hunters
indicate that the depression has strengthened.  The maximum
flight-level wind at 700 mb was 41 kt and reliable SFMR values were
35 kt.  Based on that data, the initial intensity is increased to 35
kt, making the cyclone Tropical Storm Humberto.  The data from the
aircraft indicate that the cyclone is titled to the northeast with
height, likely due to southwesterly wind shear.
Humberto has been moving erratically during the past 12 to 18 hours
as the cyclone has been trying to organize, but my best guess at the
initial motion is 320/5. During the next few days, a ridge to the
north of the system over the eastern United States and the western
Atlantic is expected to slide southeastward, with a weakness in the
ridge developing due to a mid- to upper-level trough over the
northeastern U.S.  This change in the steering pattern should cause
the storm to slow down and turn northward off the east coast of
Florida in 36 to 48 hours.  The models show the trough over the
northeastern U.S. amplifying early next week, which should cause
Humberto to turn northeastward and then eastward away from the U.S.
The NHC track forecast has been nudged south and east of the
previous one to be in better agreement with the latest consensus
models. Since there is increasing confidence that the storm will
remain well offshore of the coast of Florida, the Tropical Storm
Watch for that area has been discontinued.
The storm is still feeling some effects of southwesterly shear
and drier air, which is causing its lopsided appearance in
satellite images and strong tilt in the aircraft data.  The
atmospheric conditions are expected to gradually become more
conducive for strengthening while Humberto moves over the warm
Gulf Stream waters.  These environmental parameters support
intensification, and the cyclone is expected to become a hurricane
in 2 to 3 days.  The NHC intensity forecast is largely an update of
the previous one and in line with the HCCA and IVCN guidance.
Key Messages:
1. Humberto will likely bring tropical-storm-force winds and heavy
rainfall to portions of the northwestern Bahamas on Saturday.
Significant storm surge is not expected in the northwest Bahamas
from this system. Residents there should follow any advice given by
local officials.
2. Heavy rainfall and scattered flash flooding is possible this
weekend in coastal sections of eastern Florida, Georgia, and South
Carolina. The chance of heavy rainfall affecting coastal North
Carolina early next week continues to diminish.
FORECAST POSITIONS AND MAX WINDS
INIT  14/0300Z 25.6N  75.2W   35 KT  40 MPH
12H  14/1200Z 26.5N  76.5W   35 KT  40 MPH
24H  15/0000Z 27.6N  77.6W   40 KT  45 MPH
36H  15/1200Z 28.8N  78.2W   50 KT  60 MPH
48H  16/0000Z 29.8N  78.1W   60 KT  70 MPH
72H  17/0000Z 31.0N  75.5W   70 KT  80 MPH
96H  18/0000Z 31.3N  72.0W   75 KT  85 MPH
120H  19/0000Z 32.3N  67.2W   75 KT  85 MPH
$$
Forecaster Cangialosi

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