[Tropical] Tropical Cyclone Discussion

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WTNT45 KNHC 251447
TCDAT5

TROPICAL STORM ERIKA DISCUSSION NUMBER   3
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL052015
1100 AM AST TUE AUG 25 2015

The cloud pattern of the system has deteriorated this morning, and
deep convection is rather limited at this time.  Microwave and
high-resolution visible imagery indicates that the center is to the
north of the main area of deep convection, and the current intensity
is maintained at 40 kt based on a recent ASCAT overpass.  The Air
Force Hurricane Hunters are scheduled to investigate Erika later
today and should provide a good estimate of the strength of
the system.  The dynamical guidance indicates that the future
environment of the tropical cyclone will be characterized by
marginal humidity and around 15 to 20 kt of vertical shear.  This
should allow for only slow strengthening at best.  The official
forecast is similar to the HWRF guidance during the first half of
the forecast period, and close to the model consensus near the end
of the period.  Given the current state of the system and the
possibility of stronger shear, however, there is less than usual
confidence in the NHC intensity forecast.

The initial motion is just north of west or 280/17 kt.  The track
forecast reasoning is similar to that from the previous advisory
package.  Over the next couple of days, Erika should be steered
west-northwestward on the southern side of a subtropical ridge.
Later in the forecast period, the track models diverge with the
HWRF and U.K. Met. office models taking the system more to the
north and east of the consensus and the ECMWF and GFS farther west.
The official forecast leans toward the latter guidance and is left
of the multi-model consensus.  Given the significant spread in the
guidance in 3 to 5 days, confidence in the track forecast late in
the period is low.

FORECAST POSITIONS AND MAX WINDS

INIT  25/1500Z 15.2N  51.0W   40 KT  45 MPH
 12H  26/0000Z 15.8N  53.4W   45 KT  50 MPH
 24H  26/1200Z 16.6N  56.4W   50 KT  60 MPH
 36H  27/0000Z 17.4N  59.5W   55 KT  65 MPH
 48H  27/1200Z 18.0N  62.5W   55 KT  65 MPH
 72H  28/1200Z 20.0N  67.5W   60 KT  70 MPH
 96H  29/1200Z 22.5N  72.5W   65 KT  75 MPH
120H  30/1200Z 24.5N  75.5W   70 KT  80 MPH

$$
Forecaster Pasch
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