000
WTNT44 KNHC 201459
TCDAT4

HURRICANE DANNY DISCUSSION NUMBER   9
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042015
1100 AM AST THU AUG 20 2015

Danny's cloud pattern has continued to improve since the previous
advisory, and a 10 n mi diameter eye has become embedded in the
center of a small central dense overcast. Water vapor imagery
indicates that upper-level outflow has become more symmetrical. The
initial intensity of 65 kt is based on NHC objective Dvorak
classifications of T4.1-T4.2 using an eye feature.  Conventional and
microwave satellite images indicate that Danny is an unusually small
tropical cyclone.

Satellite fixes indicate that Danny is now moving west-northwestward
or 295/10 kt. The latest model guidance remains in very good
agreement on Danny moving west-northwestward for the next 48-72
hours toward a weakness in the subtropical ridge along 60W
longitude. A mid- to upper-level trough north of Bermuda is forecast
by the global models to begin lifting out to the north in 96-120
hours, which should allow the subtropical ridge to the north of
Danny to build back westward, forcing Danny on a more westward track
on days 4 and 5. The NHC official forecast track is essentially an
update of the previous advisory through 72 hours, but was shifted a
little north of the previous track after that in agreement with the
consensus model TVCN.

Danny's compact size makes it subject to significant fluctuations in
strength, both up and down, and such fluctuations are notoriously
difficult to forecast.  Low-shear conditions are expected to
continue for the next 36 hours or so, which argues for some further
strengthening during that time. However, the cyclone continues to be
surrounded by dry mid-level air, which could penetrate into the core
and disrupt the intensification process. By 48 hours and beyond, the
vertical wind shear is forecast to become southerly to southwesterly
and increase to near 15 kt.  As a result, Danny is expected to be
weakening as it approaches the Leeward Island.  The official
intensity forecast calls for a peak intensity somewhat higher and
earlier than the previous advisory, ending up close to the IVCN
consensus model.

FORECAST POSITIONS AND MAX WINDS

INIT  20/1500Z 12.5N  44.8W   65 KT  75 MPH
 12H  21/0000Z 13.1N  46.0W   70 KT  80 MPH
 24H  21/1200Z 14.0N  47.6W   75 KT  85 MPH
 36H  22/0000Z 14.7N  49.4W   75 KT  85 MPH
 48H  22/1200Z 15.2N  51.5W   70 KT  80 MPH
 72H  23/1200Z 16.0N  56.4W   65 KT  75 MPH
 96H  24/1200Z 16.9N  61.7W   65 KT  75 MPH
120H  25/1200Z 18.0N  66.6W   55 KT  65 MPH

$$
Forecaster Stewart

000
WTNT44 KNHC 210837
TCDAT4

HURRICANE DANNY DISCUSSION NUMBER  12
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042015
500 AM AST FRI AUG 21 2015

Danny has strengthened a little overnight.  The eye of the compact
hurricane has become more distinct recently and the cloud tops have
cooled in the eyewall.  The Dvorak classifications from TAFB and SAB
were both T4.5 at 0600 UTC, and the initial wind speed has been
nudged upward to 75 kt accordingly.  The eye of Danny passed about
75 n mi south of NOAA buoy 41041 a few hours ago and winds at that
location were only around 20 kt, indicative of the very small size
of the wind field of this hurricane.

The cyclone continues to move west-northwestward at about 9 kt.
The relatively slow forward speed of the system is due to a trough
over the western Atlantic, which has weakened the subtropical
ridge.  This trough is expected to lift northward in a couple of
days, allowing the ridge to build westward and strengthen.  The
change in the steering flow should cause Danny to turn westward and
speed up this weekend and early next week.  The track guidance
remains in good agreement, and the NHC forecast lies closest to the
consensus of the GFS and ECMWF models.  The new forecast track is
just a tad to the north of the previous one at days 4 and 5, but is
otherwise just an update.

Danny is currently in a very low wind shear environment and over
warm water, and it is expected to remain in these favorable
conditions for about another 12-24 hours.  Therefore, additional
strengthening is possible in the short term.  Beyond that time,
however, the system is expected to move into an area of increased
southwesterly shear and drier air.  These factors should induce a
weakening trend.  The NHC intensity forecast is in best agreement
with the intensity model consensus IVCN.  As mentioned in previous
discussions, the small size of the hurricane makes it susceptible to
sudden changes in intensity, which are difficult to predict.

A NOAA aircraft will be conducting a research mission in and around
Danny this afternoon, and an Air Force Reserve Unit reconnaissance
aircraft will investigate Danny Saturday afternoon.  These data
will provide a better assessment of the intensity and structure of
the hurricane.

FORECAST POSITIONS AND MAX WINDS

INIT  21/0900Z 13.7N  47.4W   75 KT  85 MPH
 12H  21/1800Z 14.3N  48.8W   80 KT  90 MPH
 24H  22/0600Z 14.9N  50.8W   75 KT  85 MPH
 36H  22/1800Z 15.5N  53.0W   65 KT  75 MPH
 48H  23/0600Z 15.9N  55.3W   60 KT  70 MPH
 72H  24/0600Z 16.7N  60.5W   50 KT  60 MPH
 96H  25/0600Z 17.8N  65.7W   45 KT  50 MPH
120H  26/0600Z 18.5N  70.5W   40 KT  45 MPH...INLAND

$$
Forecaster Cangialosi

000
WTNT44 KNHC 211438
TCDAT4

HURRICANE DANNY DISCUSSION NUMBER  13
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042015
1100 AM AST FRI AUG 21 2015

Danny has continued to strengthen during the past several hours.
The small eye has become better defined, and it is now embedded in
a circular central dense overcast.  In addition, the ragged outer
banding has increased in coverage and now surrounds the central
convection.  The initial intensity is increased to 90 kt in
agreement with satellite intensity estimates from TAFB and SAB.  It
is notable that experimental multispectral METEOSAT imagery suggests
that low-level moisture has wrapped around the cyclone and pushed
the drier air farther away.  This could be helping both the
intensification and the increase in outer banding.

The initial motion is 290/9.  The subtropical ridge north of Danny
remains weaker than normal due to a deep-layer trough over the
western Atlantic.  This trough is expected to lift northward in a
couple of days, allowing the ridge to build westward and
strengthen.  This evolution should cause Danny to turn more
westward with some increase in forward speed.  The track guidance
is in good agreement with this scenario and forecasts Danny to be
near the Leeward Islands in about 72 hours, near Puerto Rico in
about 96 hours, and near Hispaniola in about 120 hours.  The new
forecast track, which is in best agreement with the GFS and ECMWF
models, lies close to the previous forecast through 96 hours and a
little to the north of the previous forecast at 120 hours.

Danny is currently in an environment of light vertical wind shear.
However, it is about to encounter increasing upper-level
southwesterly flow associated with a trough over the northeastern
Caribbean, with the shear forecast to increase to over 20 kt by 96
hours.  This, combined with the abundant dry air remaining along the
forecast track, should cause Danny to weaken below hurricane
strength as it approaches the Caribbean islands.  The new intensity
forecast is a little stronger than the intensity consensus through
96 hours.  After that, it is weaker than most of the guidance due
to the expected interaction with land.

A NOAA aircraft will be conducting a research mission in and around
Danny this afternoon, and an Air Force Reserve Unit reconnaissance
aircraft will investigate Danny Saturday afternoon.  These data
will provide a better assessment of the intensity and structure of
the hurricane.


FORECAST POSITIONS AND MAX WINDS

INIT  21/1500Z 14.0N  48.2W   90 KT 105 MPH
 12H  22/0000Z 14.5N  49.6W   90 KT 105 MPH
 24H  22/1200Z 15.1N  51.7W   85 KT 100 MPH
 36H  23/0000Z 15.5N  54.0W   75 KT  85 MPH
 48H  23/1200Z 16.0N  56.4W   65 KT  75 MPH
 72H  24/1200Z 17.0N  61.5W   55 KT  65 MPH
 96H  25/1200Z 18.0N  66.0W   50 KT  60 MPH
120H  26/1200Z 19.5N  71.0W   40 KT  45 MPH...INLAND

$$
Forecaster Beven