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Hurricane HELENE


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Hurricane Helene Discussion Number  24
NWS National Hurricane Center Miami FL       AL082018
500 AM AST Thu Sep 13 2018

Helene's surface circulation has become fully exposed this morning
with the center decoupled about 110 miles south of edge of the
remaining deep convection.  Subjective and objective satellite
intensity estimates have decreased and support lowering the initial
intensity to 65 kt.

Statistical and global model guidance show the southwesterly shear
increasing significantly in 12 hours or so, however, the 26 to
27C sea surface temperatures should govern the weakening trend a
little.  In 3 days, Helene is forecast to move over much cooler
waters while the cyclone becomes embedded in the hostile
mid-latitude upper-level westerlies.  Subsequently, further
weakening is expected at a faster pace.  By day 4, the large-scale
models all show Helene acquiring extratropical cyclone
characteristics as it moves toward Ireland and the United
Kingdom.  The NHC intensity forecast is similar to the previous
advisory, and is based primarily on the NOAA-HCCA and the IVCN
consensus models.

Helene is still moving northward, or 355/12 kt, within the
deep-layer southerly flow produced by an amplifying mid-Atlantic
trough to the west of the cyclone.  In 48 hours, Helene is forecast
to turn north-northeastward followed by a turn toward the northeast
with an increase in forward motion at the 72 hour period.  The
guidance suite remains tightly clustered through day 4, with some
slight spread at day 5, and indicates that Helene will pass near the
Azores in about 3 days.  Interests in those islands should closely
monitor the progress of Helene over the next few days.  The official
forecast is basically an update of the previous one, and lies close
to the TVCN multi-model consensus through the entire forecast
period.


FORECAST POSITIONS AND MAX WINDS

INIT  13/0900Z 23.5N  37.3W   65 KT  75 MPH
 12H  13/1800Z 25.7N  37.4W   60 KT  70 MPH
 24H  14/0600Z 29.1N  36.9W   55 KT  65 MPH
 36H  14/1800Z 32.5N  36.2W   55 KT  65 MPH
 48H  15/0600Z 35.8N  34.7W   55 KT  65 MPH
 72H  16/0600Z 40.7N  28.2W   50 KT  60 MPH
 96H  17/0600Z 44.6N  19.5W   50 KT  60 MPH...POST-TROP/EXTRATROP
120H  18/0600Z 51.1N  10.8W   45 KT  50 MPH...POST-TROP/EXTRATROP

$$
Forecaster Roberts

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