[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 291453
TCDAT1

Tropical Storm Julian Discussion Number   3
NWS National Hurricane Center Miami FL       AL112021
1100 AM AST Sun Aug 29 2021

The system has become better organized this morning, with the
low-level center located on the southwestern edge of a persistent
mass of deep convection.  A 1246 UTC ASCAT-B pass revealed an area
of winds over 40 kt southeast of the center, so the system is
upgraded to Tropical Storm Julian with maximum winds of 45 kt.

Julian is accelerating toward the northeast (045/15 kt) in the flow
to the south of a deep-layer area of low pressure located just east
of Newfoundland.  The storm is expected to move around the
southeastern and eastern periphery of this large low during the next
few days, accelerating further and turning toward the north by 48
hours.  The track models are all in good agreement on this scenario,
and the NHC track forecast is very close to the TVCA and HCCA
consensus aids.  This new forecast is also relatively unchanged from
the previous advisory.

Winds in the storm have increased faster than expected, even in the
face of 20 kt of west-southwesterly shear.  This shear is forecast
to increase substantially in the coming days, with SHIPS diagnostics
indicating it may reach magnitudes of 40-50 kt. However, the storm
will still be moving over marginally warm waters around 26 degrees
Celsius, and its fast motion and some baroclinic forcing could allow
for additional strengthening during the next 12-24 hours.  Nearly
all the intensity models support some strengthening, and the NHC
official forecast peaks the winds at 55 kt in 24 hours, roughly
between the IVCN and HCCA solutions. Phase-space diagrams suggest
that Julian will probably already be going through extratropical
transition at that time, and it should be fully extratropical by 36
hours.  Gradual weakening is anticipated after 24 hours, and the
extratropical low is likely to dissipate over the north Atlantic by
day 3.


FORECAST POSITIONS AND MAX WINDS

INIT  29/1500Z 35.1N  46.8W   45 KT  50 MPH
 12H  30/0000Z 36.9N  43.7W   50 KT  60 MPH
 24H  30/1200Z 40.0N  39.7W   55 KT  65 MPH
 36H  31/0000Z 43.6N  37.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
 48H  31/1200Z 48.0N  36.8W   45 KT  50 MPH...POST-TROP/EXTRATROP
 60H  01/0000Z 52.2N  38.2W   40 KT  45 MPH...POST-TROP/EXTRATROP
 72H  01/1200Z...DISSIPATED

$$
Forecaster Berg
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