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Subtropical Storm Ernesto Discussion Number   5
NWS National Hurricane Center Miami FL       AL052018
500 AM AST Thu Aug 16 2018

Ernesto has generally changed little during the past several hours.
The subtropical storm continues to produce patches of convection in
curved bands around the center.  The circulation of the system is
becoming a little elongated from north to south, and dry air is
wrapping into the western portion of the system.  The initial
wind speed is again held at 35 kt, in agreement with the satellite
intensity estimate from TAFB.

The subtropical storm has a limited amount of time to strengthen as
it will remain over marginally warm waters and in a low wind
shear environment for only another 12 hours.  After that time,
the cyclone is expected to cross over a sharp SST gradient and move
into an environment of higher shear.  These conditions should cause
Ernesto to lose its tropical characteristics in about 24 hours, when
the SSTs beneath the cyclone are expected to be near 20 deg C.  The
post-tropical system will likely maintain its intensity, due in part
to its fast forward speed, until it merges with a frontal zone near
the United Kingdom this weekend.

The storm continues to gradually speed up, and it is now moving
north-northeastward at 11 kt.  A turn to the northeast with a
significant increase in forward speed is expected later today and
Friday as a pair of shortwave troughs approach the storm, causing
the system to become embedded in the mid-latitude westerlies.  The
models remain in fairly good agreement, and this track forecast is
largely an update of the previous one.

FORECAST POSITIONS AND MAX WINDS

INIT  16/0900Z 40.8N  44.1W   35 KT  40 MPH
 12H  16/1800Z 42.4N  41.9W   40 KT  45 MPH
 24H  17/0600Z 45.0N  37.7W   40 KT  45 MPH...POST-TROPICAL
 36H  17/1800Z 47.8N  31.6W   40 KT  45 MPH...POST-TROP/EXTRATROP
 48H  18/0600Z 50.6N  23.4W   40 KT  45 MPH...POST-TROP/EXTRATROP
 72H  19/0600Z...DISSIPATED

$$
Forecaster Cangialosi

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