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Post-Tropical Cyclone Chris Forecast Discussion


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574 
WTNT43 KNHC 121459
TCDAT3

Post-Tropical Cyclone Chris Discussion Number  24
NWS National Hurricane Center Miami FL       AL032018
1100 AM AST Thu Jul 12 2018

Extratropical transition has been ongoing for the past few hours,
with the rain shield continuing to expand and clouds tops warming in
the northwestern semicircle. In addition, surface observations close
to the center now show a sharp temperature gradient of almost 20 deg
F across the center, which is indicative of the cyclone having
merged with a cold frontal system. As a result, Chris has become a
post-tropical/extratropical cyclone. The intensity of 60 kt is based
on continuity with the previous advisory and earlier ASCAT
scatterometer passes. Gradual weakening is forecast by all of the
intensity model guidance, but the cyclone is still expected to
remain a gale area through 72 hours.

Chris has made a slight westward jog, but the latest model guidance
insists that the cyclone will start moving back toward the northeast
or 045 degrees at 30-31 kt. Post-tropical cyclone Chris is forecast
to remain embedded within the fast mid-latitude westerly flow on the
east side of a broad, deep-layer trough moving eastward over the
northeastern United States and southeastern Canada for the next 48
hours or so. By 72 hours, the cyclone is expected to slow down and
begin moving northward as it interacts with a larger mid-latitude
upper-level low. The NHC model guidance remains tightly packed, so
only minor adjustments to the previous advisory track were required,
and mainly in just the first 12 hours. On the forecast track, the
center of Chris is expected to pass over or near the Avalon
Peninsula of southeastern Newfoundland around 2100-0000 UTC this
afternoon and evening.

This is the last public advisory issued by the National Hurricane
Center on this system.  Additional information on this system can be
found in High Seas Forecasts issued by the National Weather Service,
under AWIPS header NFDHSFAT1, WMO header FZNT01 KWBC, and available
on the Web at https://ocean.weather.gov/shtml/NFDHSFAT1.shtml. Other
information on Post-Tropical Cyclone Chris can be found in products
issued by Environment Canada/Canadian Hurricane Centre on the
internet at weather.gc.ca/hurricane/.


FORECAST POSITIONS AND MAX WINDS

INIT  12/1500Z 44.4N  57.7W   60 KT  70 MPH...POST-TROPICAL
 12H  13/0000Z 47.7N  52.8W   55 KT  65 MPH...POST-TROP/EXTRATROP
 24H  13/1200Z 50.7N  44.7W   45 KT  50 MPH...POST-TROP/EXTRATROP
 36H  14/0000Z 53.5N  35.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
 48H  14/1200Z 56.5N  26.5W   35 KT  40 MPH...POST-TROP/EXTRATROP
 72H  15/1200Z 61.6N  18.9W   35 KT  40 MPH...POST-TROP/EXTRATROP
 96H  16/1200Z...DISSIPATED

$$
Forecaster Stewart