Hurricane Chris Discussion Number  17
NWS National Hurricane Center Miami FL       AL032018
500 PM EDT Tue Jul 10 2018

Reports from an Air Force Reserve hurricane hunter aircraft indicate
that Chris has finally attained hurricane status, making it the
second hurricane thus far this season, which is ahead of climatology
by more than six weeks. The aircraft found 850-mb flight-level winds
of 88 kt in the southeastern quadrant, along with SFMR winds of
73-77 kt. Dropsondes in the the same area found equivalent surface
winds of 73-74 kt, and the most recent central pressure observed was
980 mb. Furthermore, satellite intensity estimates are a consensus
T4.5/77 kt from TAFB, SAB, and UW-CIMSS ADT, based on a well-defined
20-nmi-diameter clear eye. These data support a solid 75-kt advisory
intensity.

The initial motion is a slightly faster 050/09 kt. Chris is north of
a narrow subtropical ridge, and water vapor imagery also indicates
that Chris is beginning to feel the influence of a digging trough
over the northeastern U.S. and Mid-Atlantic states. The combination
of these two features should gradually accelerate the hurricane
northeastward at a faster forward speed through 96 hours. By the
time Chris passes well southeast of Nova Scotia in 36 hours or so,
the hurricane will be moving at a forward speed of more than 25 kt.
On the new forecast track, Chris is still expected to move near or
over southeastern Newfoundland in about 48-60 hours. The latest
model guidance has a much larger spread in both cross-track and
along-track motions. To smooth out these differences, the new
forecast track is down the middle of the tighter HCCA, FSSE, and
TVCN consensus model suite.

Now that Chris has moved away from the cold upwelling region, some
additional intensification is forecast for the next 12 hours or so
due to 27-28 deg C SSTs beneath the cyclone and the well-established
current outflow pattern that is expected to persist during that
time. Slow weakening should begin shortly after Chris peaks in
intensity due to the cyclone moving over cooler waters, creating
some modest upwelling as a result. By 36 hours, Chris will have
moved well north of the Gulfstream and be moving over SSTs colder
than 15 deg C. The combination of the much colder water and
southwesterly vertical wind shear in excess of 30 kt should induce a
rapid transition to an extratropical cyclone. The official intensity
forecast is above the intensity guidance through 12 hours, and then
shows weakening after that similar to the LGEM and IVCN models.

Now that Chris is moving away from the United States, the
previously scheduled aircraft mission for 11/0600 UTC has been
canceled.

FORECAST POSITIONS AND MAX WINDS

INIT  10/2100Z 33.7N  72.4W   75 KT  85 MPH
12H  11/0600Z 34.9N  70.7W   85 KT 100 MPH
24H  11/1800Z 37.1N  67.4W   80 KT  90 MPH
36H  12/0600Z 40.5N  62.6W   75 KT  85 MPH
48H  12/1800Z 44.7N  57.0W   60 KT  70 MPH...POST-TROP/EXTRATROP
72H  13/1800Z 51.0N  41.2W   50 KT  60 MPH...POST-TROP/EXTRATROP
96H  14/1800Z 55.2N  22.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
120H  15/1800Z 59.0N  12.5W   35 KT  40 MPH...POST-TROP/EXTRATROP

$$
Forecaster Stewart