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Tropical Depression EIGHT Forecast Discussion


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000
WTNT43 KNHC 281451
TCDAT3

TROPICAL DEPRESSION EIGHT DISCUSSION NUMBER   1
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL082016
1100 AM EDT SUN AUG 28 2016

The area of low pressure located west of Bermuda has been producing
intermittent organized deep convection for the last 24 hours or so,
and the convection has increased markedly since 06Z.  Given this,
and the well-defined center shown by an overnight ASCAT pass,
advisories are now being initiated on this system as a tropical
cyclone.  The initial intensity is estimated to be 30 kt based on
the latest Dvorak estimates of T2.0/30 kt from TAFB and SAB.  An Air
Force Reserve Hurricane Hunter aircraft is scheduled to investigate
the depression this afternoon.

The environment is only expected to be marginally conducive for
intensification, with moderate southeasterly to easterly shear
expected to become southwesterly and increase further in 36 to 48
hours.  As a result, only modest strengthening is shown in the
official forecast, with the depression expected to become a tropical
storm in the next day or two.  After that time, the global models
show the cyclone opening up along a frontal zone well offshore of
the northeastern United States.  However, there is some disagreement
in when this will occur, with the GFS showing the cyclone
dissipating in about 3 days, and the ECMWF hanging onto it until
around day 5.  As a compromise, the NHC forecast shows dissipation
after day 4, but this timing is quite uncertain.

The depression is currently situated south of a mid-level ridge that
extends from the Mid-Atlantic states into the western Atlantic, and
the initial motion estimate is 280/08.  The ridge is forecast to
break down and shift eastward during the next 2-3 days, which should
result in the cyclone gradually turning poleward and then recurving
during the next 72 hours.  The NHC track forecast is close to a
blend of the GFS and ECMWF models through dissipation.  This
forecast keeps the center of the cyclone east of the Outer Banks of
North Carolina, but a tropical storm watch may be needed for that
area later today.

Based on an evaluation of satellite imagery and data during the past
few days, it appears that the remnants of Tropical Storm Fiona are
not directly responsible for the genesis of this depression.  The
Fiona remnants were absorbed into a separate area of pre-existing
vorticity, with the current depression developing out of the
combined system.  As a result, this is considered to be a new
tropical cyclone, not a regeneration of a previous tropical
cyclone.

FORECAST POSITIONS AND MAX WINDS

INIT  28/1500Z 31.5N  70.0W   30 KT  35 MPH
 12H  29/0000Z 32.1N  71.6W   30 KT  35 MPH
 24H  29/1200Z 32.9N  73.3W   30 KT  35 MPH
 36H  30/0000Z 33.6N  74.4W   35 KT  40 MPH
 48H  30/1200Z 34.2N  75.0W   35 KT  40 MPH
 72H  31/1200Z 36.5N  73.0W   35 KT  40 MPH
 96H  01/1200Z 39.0N  66.5W   35 KT  40 MPH...POST-TROP/EXTRATROP
120H  02/1200Z...DISSIPATED

$$
Forecaster Brennan