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HURRICANE JOAQUIN DISCUSSION NUMBER  18
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL112015
500 AM EDT FRI OCT 02 2015

The eye of Joaquin has not been apparent in recent infrared imagery.
The last pass of the Hurricane Hunter aircraft through the center
around 04Z showed indications of a double wind maximum at flight
level, which could indicate that an eyewall replacement cycle is
underway. The last report from the aircraft indicated that the
central pressure still around 935 mb. The initial intensity remains
115 kt pending the arrival of the next aircraft before 12Z. Some
fluctuations in intensity are possible during the next 12 to 24
hours due to eyewall replacement. After that time, gradual weakening
is forecast as the cyclone encounters increasing southwesterly
shear, but Joaquin is expected to remain a powerful hurricane for
the next several days. Faster weakening in shown late in the period
as the cyclone is forecast move over cooler waters and the shear
increases further.

The initial motion estimate is a slow drift toward the northwest, or
315/03, with the hurricane now gaining a bit of latitude based on
recent center fixes. The ridge north of Joaquin will weaken in the
next 12 to 24 hours as a mid/upper-level low moves in from the east,
and the hurricane should begin to move more quickly northward today
and then accelerate northeastward tonight and Saturday. The track
model guidance is in reasonable agreement on this scenario, and the
NHC forecast during the first 2 days is a little to the right of the
previous one, trending toward the latest multi-model consensus.

After that time, there have been some changes in the latest models,
with the GFS trending west from its previous forecast with a track
still offshore but closer to Cape Cod in about 5 days. The ECMWF has
also trended westward this cycle away from Bermuda and now lies
closer to the middle of the guidance suite. The UKMET is now the
eastern-most model, but still shows a track west of Bermuda. The
spread in the guidance at these time ranges appears to be due to
differences in the strength and speed of the westward movement of
the upper-level low passing north of Joaquin in the next 2 to 3
days. The new NHC forecast at days 3 and 4 has been shifted a little
to the east of the previous one and now lies near the latest
consensus aids. At day 5, all of the guidance shows the cyclone
accelerating east-northeastward, and the NHC track reflects this
trend. Given the continued variability in the guidance from cycle to
cycle, further adjustments will likely be needed to the NHC track at
days 3 through 5.

KEY MESSAGES:

1.  Joaquin's slow motion means that extremely dangerous conditions
will continue over portions of the warning areas in the Bahamas
today.

2.  The forecast models continue to indicate a track offshore of the
United States east coast from the Carolinas to the mid-Atlantic
states, and the threat of direct impacts from Joaquin in those areas
is decreasing.  However, there is still uncertainty in how close
Joaquin could come to Bermuda, extreme southeastern New England/Cape
Cod, and Nova Scotia during the next several days, and interests in
those areas should continue to monitor the progress of the
hurricane. A Tropical Storm or Hurricane Watch could be required for
Bermuda later today.

3.  Efforts to provide the forecast models with as much data as
possible continue, with twice daily NOAA G-IV jet missions in the
storm environment, and extra NWS balloon launches.

4.  Even if Joaquin remains offshore, strong onshore winds
associated with a frontal system will create minor to moderate
coastal flooding along the coasts of the mid-Atlantic and
northeastern states through the weekend.  In addition, very heavy
rains, not associated with Joaquin, are expected to produce flooding
over portions of the Atlantic coastal states.  Please see products
issued by local NWS Forecast Offices.

FORECAST POSITIONS AND MAX WINDS

INIT  02/0900Z 23.3N  74.7W  115 KT 130 MPH
 12H  02/1800Z 23.9N  74.8W  115 KT 130 MPH
 24H  03/0600Z 25.4N  74.0W  115 KT 130 MPH
 36H  03/1800Z 27.4N  72.5W  110 KT 125 MPH
 48H  04/0600Z 30.0N  70.9W  100 KT 115 MPH
 72H  05/0600Z 34.8N  69.1W   85 KT 100 MPH
 96H  06/0600Z 39.0N  66.0W   65 KT  75 MPH
120H  07/0600Z 43.5N  54.5W   55 KT  65 MPH

$$
Forecaster Brennan

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