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TROPICAL STORM HENRI DISCUSSION NUMBER   8
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL082015
500 PM AST THU SEP 10 2015

Henri continues to struggle with most of its deep convection well
removed to the northeast of the center.  In fact, it is taking on
some characteristics of a subtropical cyclone with recent
scatterometer data indicating that the radius of maximum winds has
increased to a rather high value of 120 n mi.  The initial wind
speed will remain 35 kt on the basis of 30-35 kt winds observed in
partial scatterometer pass that missed the area that likely
has the strongest winds.

Southerly shear is still forecast to relax overnight near Henri,
which theoretically could result in intensification during the next
day or so before the cyclone moves over cold water on Saturday.
However, dry air aloft persists near the storm and the overall cloud
pattern is quite disorganized. The unfavorable factors are starting
to outweigh the favorable conditions, so the official intensity
forecast is reduced from the previous one, a little below the model
consensus.  Extratropical transition is expected within 2 days due
to strong shear and very cold water.  A reasonable alternative
solution provided by some of the global models is that the cyclone
stays weak and opens up into a trough during the day on Friday.

Henri is moving faster to the north, now about 13 kt.  The storm
should continue to accelerate northward tonight and northeastward
tomorrow due to it encountering faster steering from the subtropical
ridge.  After that time, an even faster northeastward and then
eastward motion is predicted when the cyclone becomes embedded in
the mid-latitude flow.   The guidance has trended to the left
with the track of Henri, perhaps due to a weaker forecast
representation of the storm.  The NHC forecast is shifted in that
direction, although remains on the right side of the guidance
envelope.  If it survives, the cyclone should become absorbed by a
larger extratropical low by day 4 over the far North Atlantic.

The latter part of this forecast, when the storm is expected to be
post-tropical, is based on guidance provided by NOAA's Ocean
Prediction Center.


FORECAST POSITIONS AND MAX WINDS

INIT  10/2100Z 33.9N  60.7W   35 KT  40 MPH
 12H  11/0600Z 36.1N  60.3W   40 KT  45 MPH
 24H  11/1800Z 39.7N  59.1W   40 KT  45 MPH
 36H  12/0600Z 43.5N  56.5W   40 KT  45 MPH
 48H  12/1800Z 46.8N  51.8W   40 KT  45 MPH...POST-TROP/EXTRATROP
 72H  13/1800Z 48.5N  36.5W   35 KT  40 MPH...POST-TROP/EXTRATROP
 96H  14/1800Z...DISSIPATED

$$
Forecaster Blake

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