[Tropical] Tropical Cyclone Discussion

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WTNT45 KNHC 060236
TCDAT5

Hurricane Danielle Discussion Number  20
NWS National Hurricane Center Miami FL       AL052022
300 AM GMT Tue Sep 06 2022

Danielle's cloud pattern has deteriorated during the past
several hours.  The outer curved band cloud tops have warmed while
becoming ragged, and the eye temperature has cooled while becoming
partially obscured.  A recent microwave image, however, indicated
very little vertical tilt while maintaining a symmetric structure.
A blend of the subjective satellite intensity estimates from TAFB
and SAB along with the AI-enhanced Advanced Dvorak Technique (AiDT)
from UW-CIMSS yields an initial intensity of 70 kt for this
advisory.  Danielle's wind radii profile was expanded a bit in the
east semicircle based on recent METOP-B/C scatterometer data.

The cyclone should gradually spin down as it traverses cooler SSTs
of less than 22C by mid-period.  The GFS/ECMWF/UKMET continue to be
in agreement that Danielle will complete its extratropical
transition on Thursday, although the vertical thermal structure
shows the system maintaining a warm core above 600 mb.  Over the
weekend, Global model simulated IR imagery, and the Cyclone Phase
Analysis show Danielle merging with a baroclinic system approaching
from the west and developing a warm seclusion structure (shallow
warm core with a cold core upper troposphere).  Although not
explicitly indicated in the official forecast, Danielle could
maintain its intensity during this evolution is due to dynamic
forcing/favorable jet finger support while it tracks cyclonically
over the central-north Atlantic. The NHC intensity forecast
resembles the IVCN intensity consensus which has performed well so
far on the system.

Danielle should still move generally northeastward in the
deep-layer mid-latitude steering flow through the afternoon hours.
Danielle is forecast to turn east-northeast on Wednesday while
accelerating.  Toward the end of the week, as mentioned above, the
cyclone is expected to interact with a baroclinic system, while
rotating cyclonically north of the westerlies, then turn toward the
southeast.  The only significant change in the official forecast
track is the implementation of the cyclonic turn around day 3-4,
which is based on the majority of the global models.


FORECAST POSITIONS AND MAX WINDS

INIT  06/0300Z 41.6N  42.6W   70 KT  80 MPH
 12H  06/1200Z 42.2N  41.6W   65 KT  75 MPH
 24H  07/0000Z 42.8N  39.5W   65 KT  75 MPH
 36H  07/1200Z 43.9N  36.9W   65 KT  75 MPH
 48H  08/0000Z 45.5N  34.1W   60 KT  70 MPH
 60H  08/1200Z 47.4N  31.6W   55 KT  65 MPH...POST-TROP/EXTRATROP
 72H  09/0000Z 49.2N  30.1W   50 KT  60 MPH...POST-TROP/EXTRATROP
 96H  10/0000Z 49.8N  31.6W   45 KT  50 MPH...POST-TROP/EXTRATROP
120H  11/0000Z 46.8N  26.1W   40 KT  45 MPH...POST-TROP/EXTRATROP

$$
Forecaster Roberts
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