Tropical Storm FRED Forecast Discussion

000
WTNT41 KNHC 050237
TCDAT1

TROPICAL STORM FRED DISCUSSION NUMBER  25
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL062015
1100 PM AST FRI SEP 04 2015

An ASCAT-A pass just before 0000 UTC showed a small area of 35-kt
winds northeast of Fred's center, and that is the basis for the
initial intensity, making Fred a tropical storm once again. The
central pressure has been adjusted upward to 1009 mb based on
observations from drifting buoy 13519, as it appears Fred is now
embedded in an environment of higher pressure.  Despite rather
hostile vertical shear, Fred has managed to maintain enough
organized deep convection during the past couple of days to stave
off post-tropical status. The latest burst of convection is now
moving away from the low-level center, but this bursting pattern
seems likely to continue for the next couple of days as the cyclone
moves over gradually warmer waters in moderate to strong shear.
Since Fred has survived this long, it seems less likely that the
cyclone will become post-tropical in the short term, and that is no
longer shown in the official forecast. However, given our limited
ability to predict convective scale changes, this still remains a
possibility.

Little significant change in intensity is shown in the first 48
hours, as the guidance shows Fred between 30 and 35 kt during that
time. Subsequently, as the shear weakens all of the guidance shows
at least some strengthening. The NHC forecast shows only a modest
re-intensification later in the period, given the possibility that
the circulation of Fred could open up or be absorbed in 4 or 5 days
as shown by the GFS and ECMWF models.

The initial motion estimate is 290/09, and Fred should begin to move
around the western periphery of the subtropical ridge during the
next couple of days and then turn northeastward in the mid-latitude
westerlies. This cycle the models have trended faster with the
forward speed of Fred, and have shown a northward shift after 48
hours. The NHC forecast has been adjusted to account for these
trends, but now lies on the right side of the guidance envelope at
days 3 through 5. Given the large spread at these time ranges, and
the possibility that Fred could be absorbed or dissipate late in the
period, the extended portion of the track forecast is of lower than
normal confidence.

FORECAST POSITIONS AND MAX WINDS

INIT  05/0300Z 22.8N  40.1W   35 KT  40 MPH
 12H  05/1200Z 23.2N  41.1W   35 KT  40 MPH
 24H  06/0000Z 23.9N  42.2W   30 KT  35 MPH
 36H  06/1200Z 25.3N  42.7W   30 KT  35 MPH
 48H  07/0000Z 27.1N  41.7W   30 KT  35 MPH
 72H  08/0000Z 30.5N  38.0W   35 KT  40 MPH
 96H  09/0000Z 34.5N  33.5W   35 KT  40 MPH
120H  10/0000Z 36.0N  30.5W   35 KT  40 MPH

$$
Forecaster Brennan