TROPICAL STORM JOAQUIN DISCUSSION NUMBER 41
NWS NATIONAL HURRICANE CENTER MIAMI FL AL112015
500 PM AST WED OCT 07 2015
Joaquin has begun its transition into an extratropical cyclone.
The cyclone's cloud pattern has become rather asymmetric, with the
center partially exposed on the west side of weakening deep
convection. In addition, cold air is wrapping into the western
periphery of the circulation, with a warm frontal band becoming
better defined well northeast of the center. Earlier ASCAT data
still showed a large area of 55 to 60 kt winds, so the initial wind
speed is held at 60 kt.
The storm should gradually lose strength while it moves over
progressively colder waters north of the Gulf Stream. Deep
convection should disappear tonight when the SSTs drop below 20C,
and Joaquin is expected to become post-tropical at that time.
Global
models are in good agreement on the cyclone becoming a large
extratropical low on Thursday when frontal features are forecast to
form near the center. The official intensity forecast is basically
an update of the previous one, and remains in close agreement with
the GFS forecast.
Joaquin is speeding eastward at 32 kt, embedded in strong westerly
flow north of the subtropical ridge, which should keep the cyclone
moving to the east or east-northeast at a slower forward speed for
another day or two. Thereafter, the cyclone should slow down even
more and turn east-southeastward due to it coming under the
influence of a developing deep-layer trough over western Europe.
The guidance continues to migrate southward, and the official
forecast is moved in that direction, near a blend of the Florida
State Superensemble and the ECMWF models.
The track, intensity, and wind radii forecasts for 12 hours and
beyond are primarily based upon guidance provided by the Ocean
Prediction Center.
