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HURRICANE JOAQUIN DISCUSSION NUMBER  33
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL112015
500 PM AST MON OCT 05 2015

Joaquin's cloud pattern has actually improved somewhat since the
previous advisory with a cloud-filled eye having briefly appeared
in visible satellite imagery. Also, the eye has remained distinct
on the Bermuda radar at an altitude above 32,000 feet. Satellite
intensity estimates are T4.5/77 kt from SAB, T4.3/72 kt from the
NHC AODT technique, and T4.0/65 kt from TAFB. Based on the distinct
eye feature noted in visible satellite imagery and radar data, the
intensity is being maintained at 75 kt for this advisory. This
intensity is also supported by dropsonde data from the NASA WB-57
aircraft, which has been conducting research in Joaquin for the
Office of Naval Operation's Tropical Cyclone Intensity experiment.

The initial motion estimate is 030/10 kt. Joaquin is rounding the
northwestern periphery of a weak ridge located to its southeast,
and will be entering the faster mid-latitude westerlies by Tuesday
morning. The result should be a gradual turn toward the northeast
accompanied by a modest increase in forward speed tonight and
Tuesday, followed by more significant acceleration toward the
east-northeast at forward speeds of near 30 kt by Wednesday. The
official forecast track is a tad to the left of the previous
advisory track, and basically lies down the middle of the tightly
packed guidance envelope through 36 hours. At 48-120 hours, the
extratropical forecast track is based on guidance provided by the
NOAA Ocean Prediction Center.

The deep-layer vertical wind shear is expected to remain at less
than 20 kt for the next 24 hours or so, which should allow for
Joaquin to only slightly weaken. By 36 hours and beyond, westerly
vertical wind shear is forecast by the global and regional models to
increase to more than 30 kt when Joaquin will be moving over sub-24C
sea-surface temperatures. The expected result should be steady
weakening and a transition to a large and expanding extratropical
low pressure system over the much cooler waters of the north
Atlantic by 48 hours. However, the GFS and ECMWF models are
suggesting that Joaquin could get a baroclinic boost as it interacts
with a frontal system and strong jetstream and, as a result, the
intensity forecast does not show the typical rapid decay rate of a
tropical cyclone moving over 17C-20C SSTs on days 3-5. The NHC
intensity forecast is similar to the previous advisory and follows
the intensity consensus model IVCN through 36 hours, and then is
based on guidance provided by the Ocean Prediction Center for the
48-120 hour period.

FORECAST POSITIONS AND MAX WINDS

INIT  05/2100Z 35.8N  64.0W   75 KT  85 MPH
 12H  06/0600Z 37.1N  61.7W   70 KT  80 MPH
 24H  06/1800Z 38.7N  57.3W   70 KT  80 MPH
 36H  07/0600Z 40.0N  51.0W   65 KT  75 MPH
 48H  07/1800Z 41.4N  43.4W   60 KT  70 MPH...POST-TROP/EXTRATROP
 72H  08/1800Z 44.0N  28.8W   55 KT  65 MPH...POST-TROP/EXTRATROP
 96H  09/1800Z 45.6N  20.7W   50 KT  60 MPH...POST-TROP/EXTRATROP
120H  10/1800Z 48.0N  14.0W   45 KT  50 MPH...POST-TROP/EXTRATROP

$$
Forecaster Stewart

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