212 
WTNT43 KNHC 112047
TCDAT3

Hurricane Chris Discussion Number  21
NWS National Hurricane Center Miami FL       AL032018
500 PM AST Wed Jul 11 2018

The eye of Chris has become a little less distinct and more
cloud filled during the past few hours, but the overall cloud
pattern remains quite impressive in satellite imagery. The
respective wind radii were adjusted outward based on a 1454 UTC
ASCAT-A overpass, which included one 65-kt surface wind vector in
the southeastern quadrant. The initial intensity has been lowered
slightly to 80 kt based on a blend of Dvorak intensity estimates of
T4.5/77 from both TAFB and SAB, and an ADT estimate of T5.2/95 kt.

The initial motion estimate is now 050/22 kt. Little change was made
to the previous advisory track. Chris is now embedded within deep
southwesterly flow ahead of a broad trough that is digging
southeastward along the U.S. Northeast and Mid-Atlantic coasts. The
global models are in excellent agreement that the hurricane should
continue to accelerate northeastward for the next 72 hours, passing
over or near southeastern Newfoundland in 24-36 hours as a strong
extratropical cyclone. In contrast to several previous model runs,
the latest NHC guidance shows very little cross-track spread or
speed differences, and is tightly packed about the previous advisory
track. The new forecast track closely follows the previous forecast
and the consensus track models HCCA, TVCN, and FSSE.

During next 6 hours or so, Chris will be passing over a ocean
thermal ridge consisting of SSTs of more than 28 deg C, which is
associated with the Gulf Stream. As a result, little change in
strength is expected during that time. However, by 24 hours and
beyond, the cyclone will be moving over SSTs colder than 12 deg C
and encountering southwesterly vertical wind shear in excess of
30 kt, a detrimental combination that will induce rapid weakening
and also result in transition to an extratropical cyclone. The new
intensity forecast is a little lower than the various intensity
model forecasts to account for stronger shear and colder water.

FORECAST POSITIONS AND MAX WINDS

INIT  11/2100Z 37.8N  65.7W   80 KT  90 MPH
 12H  12/0600Z 40.6N  61.9W   75 KT  85 MPH
 24H  12/1800Z 44.9N  56.2W   60 KT  70 MPH...POST-TROP/EXTRATROP
 36H  13/0600Z 48.8N  49.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
 48H  13/1800Z 51.9N  40.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
 72H  14/1800Z 58.4N  22.6W   35 KT  40 MPH...POST-TROP/EXTRATROP
 96H  15/1800Z 63.0N  14.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
120H  16/1800Z...DISSIPATED

$$
Forecaster Stewart