Official Discussion issued by the National Hurricane Center

Joyce (AL102018) DATA RELEASED: 9/12/2018 11:00:00 PM UTC

Copy of official data

Subtropical Storm Joyce Discussion Number   2
NWS National Hurricane Center Miami FL       AL102018
1100 PM AST Wed Sep 12 2018

Joyce still has subtropical characteristics. Although a small area
of convection has recent developed near the storm's center, cloud
tops are not particularly cold and the cyclone is still co-located
with an upper-level low. The initial intensity has been held at 40
kt based on a subtropical intensity estimate of 35-40 kt from
TAFB.  This could be generous estimate since a recent near-miss of
the ASCAT instrument to the west of Joyce suggested that the winds
may have decreased somewhat since earlier today.

Little change has been made to the track or intensity forecast.
Just about all of the intensity guidance continues to indicate that
some gradual strengthening is possible during the next day or two
while Joyce continues to acquire tropical characteristics. By 72 h,
the global and statistical models depict Joyce weakening due to a
drastic increase in shear and a decrease in environmental humidity
until it is absorbed into a larger mid-latitude trough around 96 h.
The HWRF and HMON models show a very different solution where Joyce
strengthens to hurricane strength despite the marginal environment.
This scenario seems less likely at this time, so the NHC intensity
forecast is just below the intensity consensus beyond 36 h.

Joyce is caught in fairly light steering currents between strong
ridges to its east and west, and the initial motion estimate is
220/5 kt. All of the global models forecast only a slow
southwestward motion during the next couple of days, particularly
as Hurricane Helene approaches from the southeast. Once Helene
passes to the east, Joyce will likely quickly turn northeastward and
accelerate ahead of the aforementioned mid-latitude trough before
dissipating southwest of the Azores. The official track forecast is
basically a blend of the previous advisory and the corrected
consensus aids HCCA and FSSE.


INIT  13/0300Z 34.1N  42.6W   40 KT  45 MPH
12H  13/1200Z 33.5N  43.3W   40 KT  45 MPH
24H  14/0000Z 32.9N  43.8W   45 KT  50 MPH...TROPICAL STORM
36H  14/1200Z 32.5N  44.0W   50 KT  60 MPH
48H  15/0000Z 32.3N  43.4W   50 KT  60 MPH
72H  16/0000Z 34.2N  40.0W   45 KT  50 MPH
96H  17/0000Z 37.0N  33.5W   40 KT  45 MPH
120H  18/0000Z...DISSIPATED

Forecaster Zelinsky